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#Post#: 70430--------------------------------------------------
Homelite 25/30cc Red Neck Hop-up Techniques, Timing numbers, Etc
By: 660magnum Date: March 20, 2016, 12:03 pm
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[center]HOMELITE 25cc HOP UP[/center]
[center]Written and pictures by Av8tor
Formatting and presentation arrangement by 660magnum[/center]
This article is specifically about the Homelite 25cc, and
pertains to the Homelite 30cc engine in most respects as well.
However, the port measuring and porting techniques apply equally
well to most small two stroke engines. I hope you find it
helpful.
First and foremost, it is important that one never attempt to
“hop up” a worn engine. The results will be frustrating at
best. All important components should be in perfect condition,
and I always recommend starting with a new ring as well. I have
seen engines that still ran pretty well gain 800 rpms by only
replacing a worn ring.
Second, a coordinated approach is always needed when hopping up
any engine. The modifications need to work together to achieve
good results. It does no good to bolt on a huge carburetor for
example, and leave the stock, restrictive exhaust in place.
Common errors such as this create an engine that actually runs
worse than stock.
Third, unless you are willing to go through a lot of parts and
do a lot of testing, stick to known, proven modifications.
Parts cost a lot of money, and if you make a modification that
doesn’t work, well, you just created an expensive paper weight.
Don’t re-invent the wheel….
And lastly, don’t “polish” the ports. Just a nice finish with a
small sanding drum to clean up the casting is all that is
necessary. “Polishing the Ports” is old tech, and it has been
proven that a slightly rough port actually flows somewhat better
than a mirror smooth port. Seems odd, but it’s not if you know
some of the intricacies of fluid dynamics.
You will need the proper tools of course. Torx drivers,
screwdrivers, etc., etc. as normal, plus a few special tools.
Here are some that I use:
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082720&d=1426867870[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082721&d=1426867871[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082722&d=1426867871[/img]
Most of them are self explanatory. The small light on the end
of a flex cable is my favorite for checking port timing as I can
insert it inside the engine and really see when a port opens or
closes. The Dremel cutters are all carbide. Don’t try to use
grinding stones on aluminum or magnesium! They will immediately
clog up, then can over heat and explode! Lastly for the Dremel
is a small sanding drum tool. (Good for final dressing up of
the ports.) The tool that looks like a spark plug is my
Positive Stop for finding TDC, (Top Dead Center), and the last
is a length of PVC tubing with a piece of thick, hard emery sand
paper securely glued onto the end. This is for removing the
squish band. A person should also have some small jeweler’s
files in flat and round. They should be heated and have the
last 1.5” or so bent at about a 20 to 30 degree angle. These
are for dressing and chamfering the edges of the ports to
prevent damage to the piston and/or ring. I do it with the
small round carbide tool in my Dremel, but, one slip and, well,
remember what I said about expensive paper weights?
I don’t need to mention about eye protection and a dust mask for
use while porting and grinding on metal do I? Didn’t think so….
The first step, after disassembly, and a thorough cleaning and
inspection of parts, is to mock up the engine the first time to
take baseline measurements. Hopefully, we already have the
Frank Bowman modified piston and special ring in hand. Then we
start taking our baseline measurements, but one of the
measurements will require the squish band to be removed first,
so I do that using the PVC tube with the stiff sand paper glued
on it. The PVC tube is a nice smooth slip fit into the
cylinder. One could make a special cutter to do this, but
unless you do a lot of engines it wouldn’t be worth it. Just
use the sand paper tool. Push it up against the squish band and
push and turn to remove the band. Check often, and be very
careful not to scar or score the cylinder bore with the tool.
You are done when you can insert a screwdriver or scribe into
the cylinder head area, and no longer feel that “step” around
the outer edge of the combustion area. Here is the cylinder
with the squish band ground out.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082723&d=1426867872[/img]
Another thing we are going to be doing is to “stuff the
crankcase”, and now is a good time to take a measurement of that
to see what will be required. As you can see, there is quite a
large gap between the crank pin and the backing plate. We want
to reduce that to about .025” for better engine efficiency.
(Increased secondary compression ratio.)
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082724&d=1426867872[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082725&d=1426867873[/img]
Now we can do the first mock up assembly and start taking actual
measurements.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082738&d=1426869530[/img]
First we set up the degree wheel and pointer by finding TDC.
This is the only proper way to find Top Dead Center of the
piston, and is called the “Positive Stop Method”. You install
your positive stop, (seen screwed into the head in the picture
above), and set the degree wheel and pointer so that it shows
the exact same degree reading whether the piston is up against
the stop going in one direction, or the other. In this case the
piston hits the stop at 35 degrees when I rotate the engine
clockwise, and when I rotate the engine all the way around
counterclockwise and the piston hits the stop again, it also
shows exactly 35 degrees. You move the degree wheel or the
pointer as necessary to achieve this; equal in both directions.
Now, and only now, when you take the Positive Stop out and the
pointer shows “TDC”, the piston is actually and truly at Top
Dead Center. Now we can take the port timing measurements.
Here’s what I got for stock readings:
INTAKE OPEN: 60 degrees BTDC
INTAKE CLOSE: 60 degrees ATDC
Total Duration = 120 degrees
EXHAUST OPEN: 106 ATDC
EXHAUST CLOSE: 74 ABDC
Total Duration = 148 degrees
A special note here because I know people will ask. Here’s how
you find that exhaust duration:
180 – 106 = 74 degrees. 74 (from ATDC to BDC) + 74 (ABDC) = 148
total degrees the exhaust port is open. If it is easier for
you, just count the total open degrees on the degree wheel.
This is just a baseline measurement. This is an older engine,
so the exhaust duration is not too bad. Newer engines have been
coming out generally with a much lower exhaust port duration.
However, the intake duration is rather low. All this will
change however, when we lower the cylinder to raise the
compression. When the cylinder is lowered, the exhaust port
timing is lowered, and the intake port timing is raised. (The
exhaust port will open later, and close earlier, and the intake
will do the reverse when the cylinder is lowered.) So when we
lower the cylinder, we will lose ground with the exhaust port
total timing, but gain some with the intake. We’ll compensate
when we do our porting.
Next, while working with the degree wheel in this first mockup,
I like to use my dial indicator to see how much piston movement
affects port timing. This could be figured out mathematically
using the piston stroke, rod length, and some tricky math, but
it is quick and easy to do it with the dial indicator, and fool
proof.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082739&d=1426869531[/img]
I measure how many degrees of wheel movement it takes to move
the dial indicator .100”. (For best accuracy do this test
measurement with the piston at about mid travel, and don’t try
to figure for just one degree or a smaller dial indicator amount
as it won’t be as accurate; use .100”.) In this case, 10
degrees of wheel movement moved the dial indicator .100”. So
dividing 10 into .100”, we find that each degree of the wheel
moves the piston .010”. That’s a nice easy number to work with.
Now, here is an important fact that is absolutely imperative to
remember when working with two strokes. Whatever amount you
take off a port top or bottom to change the timing DOUBLES the
timing change. This is because you are not only changing when
the port [U]opens[/U], but [B][U]also[/U][/B] when the port
[U]closes[/U].
[B][U]Example: [/U][/B]
20 degree change desired.
20 x .010” = .200”
.200” divided by 2 =.100” (Because both opening AND closing is
changed.)
.100” to remove from port opening edge for a 20 degree timing
change.
So now we know that in order to make a (for example) 20 degree
port timing change, we would remove .100” from the top of the
exhaust port or the bottom of the intake port. If we removed
.200” it would change the timing [B][U]40 degrees[/U][/B]
because remember, when we make a change to a port, it alters
BOTH the opening AND the closing of the port.
The next thing to check/measure, is the quench or squish
distance. This is also sometimes called “Deck Height”, though
that term is not exactly correct for this application. What we
need to know is the distance from the piston to the head at TDC.
The way to do that is to bend a piece of soft solder, (not
silver solder) so that it will go into the spark plug hole and
go over against the cylinder wall. We then rotate the engine
several times while holding the solder secure in one position
and making sure it is touching the cylinder wall. The piston
will smash the solder flat, which we can then measure and this
gives us the piston to head clearance. I normally use 1/8”
electrical solder for this, but the clearance was so wide in
this engine that I had to use larger diameter plumbing solder.
The pic is a bit blurry, but you can see from the gap in the
calipers that it was a large piston to head clearance. It
measured about .080”, while we want a much smaller gap of .020”.
(.015” absolute minimum for safe operation.) Lowering the
cylinder and closing up this wide gap will give a nice raise in
the compression ratio of this engine. Now we know about how
much to remove.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082740&d=1426869531[/img]
So, the crankcase is set up in the milling machine, and we
proceed to take off .060” to arrive at the .020” clearance that
we want. (I actually took a bit more off, because I like to
make a new, slightly thicker cylinder base gasket and so I
allowed for that.) Some people make up a spud to mount the
cylinder in a lathe, and remove material from the cylinder base.
I prefer to take the material off the crankcase when possible,
because then if you ever have to replace the cylinder, you won’t
have to do the machine work again. The squish clearance can
always be fine tuned with different thickness gaskets if you
take enough off the crankcase to allow for that.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082741&d=1426869532[/img]
Next comes the cylinder porting. There are several important
items to note here. One is obvious but critical; you can always
take more material off, but you can’t add it back on. So I
recommend that you take perhaps half of what you calculated you
would need to, and then mock the engine up again, and measure
your port timings. See if they are what would be expected for
the amount you took off. If you go too far, well, there we are
with a paper weight again! You might want to do the porting in
three stages instead of just two. Grind a little, check, grind
again. (Hey, if it were quick and easy anyone could do it
right??!!)
Another thing is that you must [B][U]always[/U][/B] clean up and
chamfer the port edges after grinding on them and before mocking
the engine up again. If not, the raw port edges where you
ground them will scar, score, and destroy the piston and ring.
(More paper weights!) It is your choice whether you remove the
ring or not for these mock up tests. If you do, be careful as
it is very, very easy to break a ring while taking it off or
putting it back on. If you don’t take it off, just be very
careful when assembling the engine that you don’t break the
ring. Go slow and easy, if anything needs forced, something is
not right.
So the Homelite 25cc comes with a bridged exhaust port. We have
had the piston modified with a pin and a special ring for use
with a pinned piston, all done by the Ring Master, Frank Bowman,
so we can remove that port bridge for better exhaust flow. The
pin will keep the ring from rotating and ever getting caught in
the exhaust port, so, away with that bridge!
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082742&d=1426869532[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082743&d=1426869533[/img]
As a quick side note here, that is the quick and easy way to
tell a Homelite 25cc from a Homelite 30cc. They are identical
on the outside, but the 30cc does not have an exhaust port
bridge.
Some of the later model Homelite 25 and 30cc engines have a hole
in the cylinder just above the exhaust port that leads into a
corresponding hole in the muffler. Opinions vary as to what
that hole is for, but the most probable one is that it is for
EGR, or Exhaust Gas Recirculation. We don’t want that for our
engines, so if yours has that, drill and tap it for a set screw,
and plug the hole with a set screw with Loctite. Take care that
you don’t penetrate the cylinder with the tap threads, as that
may cause a burr in the cylinder.
Now for the actual porting. There are several ways to mark the
ports for grinding, and I have used them all at one time or
another. One is to use magic marker or machinist’s Dykem to
color the area above or below the port so that it will show a
scribed mark. You can then very, very carefully position the
piston so that it’s top edge will be where you want the new top
of the port to be, and reach in through the spark plug hole and
scribe the cylinder near the port, using the piston as a guide.
Another is to do the same magic marker or Dykem marking, but use
a calipers to get your distance, and then use a right angle
scribe to make your mark. And lastly, you can also use a piece
of pin striping tape or a similar piece of tape cut from
electrical tape. Use a long tweezers or medical hemostats, and
position the tape the appropriate distance above or below the
port. You can then grind to your mark, (or the tape), but as I
mentioned I highly recommend going only part way and doing an
engine mock up and measuring/checking your results and progress.
Remember, when changing port timing we ALWAYS remove only from
the TOP of the exhaust port, or the BOTTOM of the intake port.
All in all I recommend the tape method as probably being the
easiest and most fool proof means of marking your port for
grinding. Using the bottom of a vernier calipers or using a
dial indicator are ways of gauging the distance; another would
be to find or make something of the thickness desired, to gauge
the distance you want to grind the port top or bottom. It
really is difficult working up in that small diameter cylinder
with a head that can’t be removed. So just take your time and as
I keep saying; go slow and check your work often. Here are some
porting pics.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082752&d=1426872276[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082753&d=1426872276[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082754&d=1426872277[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082755&d=1426872278[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082756&d=1426872278[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082757&d=1426872279[/img]
Resist the urge to grind out that little “nub” in the intake
port. It is there to help keep the piston ring from bulging
into the intake port and getting damaged. Leave it there.
Also, the transfer ports are not addressed in this treatise,
because they are very critical and you should only attempt
modifying them after you are very adept at porting. They must
be kept identical, both in opening times, and ANGLES! If you
mess them up, the engine might end up running worse than stock.
Just check that the transfer ports align at the cylinder to
crankcase interface, and smooth the transfer port entry slots in
the crankcase itself.
Now we will address “Stuffing the Crankcase.” I determined that
a 1/8” piece of aluminum would be the correct thickness to get
the .025” crank pin to backplate clearance I wanted, so I made a
plate out of it to the shape of the inner surface of the
backplate.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082762&d=1426873007[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082763&d=1426873007[/img]
I sanded both the back plate and the aluminum spacer, cleaned
them with acetone, and then installed the spacer using JB Weld
and a counter sunk screw in the middle. A counter sunk screw is
not really needed as the crank pin goes around the middle and
won’t hit a bolt head. However, if you use a regular bolt, be
sure to check that it doesn’t hit the connecting rod. If you
think you will ever need a crankcase pressure tap for a smoke
pump, or remote carb pulse, here would be a good place and time
to put one. Use the pressure tap to help hold the plate in
place instead of a bolt. The JB Weld actually does the holding,
the bolt is just there to firmly hold the plate in place while
the JB Weld dries, and to help me sleep better at night. It
sure would be messy if that plate ever came loose while the
engine was running….
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082764&d=1426873007[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082765&d=1426873008[/img]
Now we have a much more reasonable piston to crankpin clearance
and our crankcase is STUFFED! Note that this is another spot
where you can fine tune your clearance with gaskets. Using
thicker, thinner, and/or multiple gaskets on the backplate will
get you where you want to be; .025”.
Now on to final assembly and the last checks. Use a small
amount of two stroke oil on all bearings and give them a spin.
Don’t load the engine up, just a few drops on each bearing is
plenty.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082766&d=1426873008[/img]
A pic of the thicker cylinder gasket I made. (use notebook
cardboard, cereal boxes, file folders, etc. to make gaskets.)
Harbor Freight sells a really neat hole punch kit that makes
making gaskets fun. (Well, sort of….)
I don’t use any sealer on the base gasket normally, and NEVER
use any sealer on the carb adapter or carb gaskets.
Put a nice film of two stroke oil on the piston, ring, and
cylinder wall and put ‘er back together for the last time.
(Hopefully!)
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082767&d=1426873009[/img]
With the cylinder bolted on, a final check of the squish
distance shows a perfect .020”.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082768&d=1426873795[/img]
#Post#: 70431--------------------------------------------------
Re: Homelite 25/30cc Red Neck Hop-up Techniques, Timing number,
Etc
By: 660magnum Date: March 20, 2016, 12:12 pm
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Continued . . .
Here you can see where I used a carb gasket with a larger bore,
and have ported out the intake manifold adapter to accommodate
the larger carb bore. The manifold gets really, really thin at
the impulse port slot, and near one of the mounting screws when
you do this. On more extensive, high rpm builds, I make a dam
and add manifold surface area near that one screw using JB Weld,
and use a smaller head screw. Then, also using JB Weld, I fill
in the impulse hole and slot, and use an external pulse port and
hose to activate the fuel pump in the carb. By doing this I can
port the manifold adapter hole larger than you see here. If you
want a really nice handling engine, go with a carb with an 11mm
venturi. If you want a bit more power, a 12.7mm venturi is the
way to go, but will be a touch more finicky on adjustment and
throttle up transition. (Not too badly though; that’s the size
carb used on the Zenoah G-26 engines.)
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082769&d=1426873796[/img]
Some people like to make a metal plate that they bolt to the
back of the engine with countersunk screws, and then the plate
bolts to the firewall to mount the engine. I don’t like adding
the extra weight, and so I just use studs to mount the back
plate, and then those same studs go back through the firewall
with washers and nuts on them. Simple and light!
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082770&d=1426873796[/img]
As to the muffler, you can purchase one from various sources
that will be much better than the unmodified stock muffler. If
not, you will definitely have to modify the stock muffler to go
along with the other modifications here. It is much, much too
restrictive and power robbing. What I do, is carefully undo the
crimp that holds the muffler halves together. I then remove all
the original baffling, screens, packing, or whatever else you
might find in there. The only thing you want to leave is the two
bolt spacers. These need to be there to keep the bolts from
smashing the muffler when tightened. Then re-assemble the
muffler and crimp it back together with the bolt spacer tubes
located inside. You then need to make either one outlet with
about a 5/8” diameter tube, or two outlets with at least ½”
diameter tubes. Braze shut any other holes in the muffler, clean
it with the wire wheel on your grinder, and paint it black with
engine paint. Done this way, the muffler is actually about as
light as an aluminum muffler, because the aluminum is much
thicker than the steel. They work fine. So…
Here is the engine all assembled.
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082771&d=1426873797[/img]
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082772&d=1426873798[/img]
Final specs:
Squish distance = .020”
Crank pin to back plate clearance = .025”
Exhaust Open: 102 degrees ATDC
Exhaust Close: 76 degrees ABDC
Exhaust total: 154 degrees
Intake Open: 67 degrees BTDC
Intake Close: 67 degrees ATDC
Intake Total: 134 degrees
What I generally recommend is 150 to 155 degrees on the exhaust
and 130 to 140 degrees on the intake for operation from around
7000 to 8000 rpms or a bit above.
For operation at 9000 and slightly above, 160 to 165 on the
exhaust and about 150 on the intake seems to work well. Much
more duration than 165 degrees on the exhaust is getting into
tuned pipe area/timing.
If you are going for the higher rpms and the most power,
definitely go with the 12.7mm venturi carb.
All done and NO paper weights created! Yes!!
This engine turned an APC 16 x 8 prop at 8400 rpms on the test
stand on the first run. A bit more power and a good bit less
weight could be realized by getting rid of the magneto and going
to electronic ignition. This would also provide for easy hand
starting and an even lower idle. It handles very nicely and is
responsive throughout the rpm range. A bit more running time and
a slightly larger carb would easily see 8700 rpms on the same
prop, and CDI electronic ignition would help as well by
eliminating the drag of the magneto flywheel, and optimizing the
ignition timing. (Which should be set at 28 degrees.) This is a
very nice, reliable engine. The boat guys run these engines at
10,000 rpms, so unless you run them lean or without oil, they
should last forever at under 9000 rpms.
Here she is, singing away on her first run!
[img]
(HTM) http://www.rcuniverse.com/forum/attachment.php?attachmentid=2082773&d=1426873798[/img]
#Post#: 70432--------------------------------------------------
Re: Homelite 25/30cc Red Neck Hop-up Techniques, Timing number,
Etc
By: 660magnum Date: March 20, 2016, 12:15 pm
---------------------------------------------------------
[center]Pinning a free piston ring . . . [/center]
[center]Written by Av8tor[/center]
[center]Formatting by 660magnum[/center]
The pin should be about the diameter of the ring groove. I use a
little piece of gas welding rod. You use a drill press to drill
a perfectly straight hole about .003" smaller than the size of
the pin in the ring groove. You want to locate it where there
are no ports in the cylinder, like in between the transfer and
the exhaust port. This is critical. Then I use a bit of JB Weld
on the pin, and with the piston held in a padded "V" block, very
carefully drive the pin into the hole with a hammer and a small
pin punch. (It's a three handed deal.) Start it straight and
don't miss, or you'll ruin the ring land. Usually you size the
pin to be the full depth of the ring land plus the distance of
the hole you drilled, so as to be able to handle the pin and
drive it in properly. But the pin has to end up being only 1/2
the depth of the ring groove. So you have to very, very
carefully grind or file down the pin until it is only sticking
up halfway into the ring groove. Once again, this is critical as
if you don't get it right, you will either break Frank's special
ring when you assemble the engine, or have a tight spot there
because the pin is holding the ring up. Not good! The other
thing is most people don't realize that the piston ring must
seal on the bottom of the ring groove in the piston as well as
against the cylinder wall. If you damage the ring land, or
groove, the ring won't seal well and the engine will be down on
power.
Note that the Homelite 30cc engine, which is identical to the
25cc except for the bore size, has a pinned piston and an
exhaust port without a bridge from the factory. It weighs
exactly the same as the 25cc, and is a better candidate for your
airplane engine. As of the date of this posting, I have been
seeing Homelite 30cc engines in the Ryobi brand of string
trimmer, and in some of the Homelite brand handheld leaf
blowers.
The pin should be whatever you can find that is about the same
diameter as the width of the ring groove. It is a bit tough to
drill a hole in a ring groove that is larger than the diameter
of the groove, and often times when you try to do so, you will
break a bit and/or damage the ring groove. That's why I suggest
measuring the width of the groove, and then planning to use a
pin that is close to the same diameter. Do not quote me on this,
but it seems as though the last time I did one, which was some
time ago, I used a gas welding rod with a diameter of .063" to
make the pin.
Then, since you want a press fit in the aluminum for the pin, I
suggest precision measuring the pin with a micrometer, and then
using a drill bit that is .003" less than the diameter of the
pin for your hole in the piston. You will really need a drill
press and a "V" block for the piston for doing this procedure,
as the hole has to be perfect. If done by hand, it will surely
not be perfectly straight nor round, and you will not be able to
trust the press fit of the pin. That could be disastrous for the
engine.
The depth will vary with the different pistons encountered with
the various Homelite 25cc engines. In some cases, you will break
right through the ring land while drilling, and of course, that
is as deep as you can go. In other cases, the drill will go
partly into the piston crown, and partly into the interior of
the piston. Once again, that will determine your depth, as once
the hole breaks through to the interior of the piston, don't
bother drilling any farther. And lastly, the drill might go
entirely into the piston crown, and never break through to the
interior area of the piston. In that case, I would drill the
hole, let's say, approximately the same depth as the depth of
the ring land.
Use a tiny bit of JB Weld on the pin when punching/pressing it
in place. Just be sure to clean any excess JB Weld away before
it dries. And when you grind that pin down to be only half way
protruding into the ring groove, be super careful that you do
not damage the ring groove while doing so.
Vee block source . . .
(HTM) http://www.plastixrevolution.net/products/soft-jaw-vise-blocks?utm_medium=cpc&utm_source=googlepla&variant=365317043&gclid=CIb89t3Tw8QCFZcdgQod_ogAOQ
To align the chuck perfectly with the "V" block by chucking a
bit in the drill press, and lowering the chuck while adjusting
the position of the "V" block until the drill bit hits perfectly
in the bottom center of the "V". I then, using a very sharp fine
point punch, center punch exactly where I want to drill the hole
in the piston. (Remember that this must be in a spot of the ring
groove that will not align with any ports in the assembled
engine!) Then, using a drill bit less than half the size of the
hole I eventually want, I carefully position the piston in the
"V" block aligned with the drill bit and drill the hole. Using a
high speed on the drill press chuck, and very light pressure
when drilling the hole helps keep it on track. Once the small
guide hole is drilled, I follow up with the final size drill I
want the hole to be.
Chuck a pin vise into my drill press to drill very tiny holes.
Just be careful, as some of the cheaper pin vises do not
actually center the drill bit well in their chucks. This is not
too noticeable when using the pin drill by hand, but it will
really wobble when chucked into a drill press.
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