Pioneer P60 - low compression!

[StihlNAlberta]

Hello all ..... hope someone can help -

With my limited experience in rebuilding s-stroke engines, I have been on a mission to get my P60 back to life. I did a compression test and it was initially around 110PSI so I figured I would pop the head off and clean it up a bit. I purchased a new set of rings and gave the jug to the local stihl guy who cleaned it up a little bit. Piston looked a little scored but not bad .... and base gasket was ok and re-used.

So .... put it back together and I now pull 90 PSI on a snap-on comp. tester. It all seemed to go back together quite well with TLC + time. I tried compression testing with throttle wide open, double checked de-comp. valve, and still the same.

Pulling the jug off is not a 2 minute job as it is really tight but I made sure head was snug and rings were loose and moved freely before compressing them into the cylinder (I have a ring compressor from Baileys).

So my questions would be:

1. Base gasket. Should they not be re-used. (There were no rips)
2. Pressure test. Never done one but are they fairly simple to do and would that be it (was fine before)
3. Do I have the rings on upside down?? Do the P60 saws have directional rings and how do you tell?
4. Can de-comp. valves leak? It looked pretty old.
5. If I have new rings and some mild honing .... will the rings seat and bring the compression up to where it should be or is it way too low to start (90PSI).

Sorry bout all the questions but i'd love to get this old beast back running the way it should be!!

Guess i shouldn't have chucked the rings as well in case it was an over sized piston.

Cheers!!

 

[BrocLuno]

Well...

Decomps can leak. Rings should be pinned on one side of the piston so they don't rotate an end gap into a port?

Squirt some WD40 into spark plug hole and retest compression. If little change it is not a ring problem? If the comp jumps up, you have a ring issue

 

[leeha]

Would like to see some pic's of the cylinder.
Was there any scoring? Yes the decomps can leak
if they are old and not sealing. I never reuse a base
gasket. Your asking for trouble and could have
an air leak and toast the top end again.
Your new rings are not seated in the old cylinder
and that can cause your lower compression. Thats
why it would be nice to see some pic's.



Lee

 

[rupedoggy]

.

5. If I have new rings and some mild honing...

And that boys and girls is why you should never hone a two stroke

 

[Scooterbum]

Pull the decomp and find a plug or bolt the same size and recheck.

 

[hoss]

Pull the decomp and find a plug or bolt the same size and recheck.

+1

 

[blsnelling]

Run a tank or two through it and check it again. A light honing will not ruin a cylinder.

 

[Jacob J.]

Run a tank or two through it and check it again. A light honing will not ruin a cylinder.

It depends on what he's honing it with.

 

[hoss]

It depends on what he's honing it with.

You mean I gotta stop using gravel and a drywall mud mixer?

 

[hillwilliam]

Hello all ..... hope someone can help -

With my limited experience in rebuilding s-stroke engines, I have been on a mission to get my P60 back to life. I did a compression test and it was initially around 110PSI so I figured I would pop the head off and clean it up a bit. I purchased a new set of rings and gave the jug to the local stihl guy who cleaned it up a little bit. Piston looked a little scored but not bad .... and base gasket was ok and re-used.

So .... put it back together and I now pull 90 PSI on a snap-on comp. tester. It all seemed to go back together quite well with TLC + time. I tried compression testing with throttle wide open, double checked de-comp. valve, and still the same.

Pulling the jug off is not a 2 minute job as it is really tight but I made sure head was snug and rings were loose and moved freely before compressing them into the cylinder (I have a ring compressor from Baileys).

So my questions would be:

1. Base gasket. Should they not be re-used. (There were no rips)
2. Pressure test. Never done one but are they fairly simple to do and would that be it (was fine before)
3. Do I have the rings on upside down?? Do the P60 saws have directional rings and how do you tell?
4. Can de-comp. valves leak? It looked pretty old.
5. If I have new rings and some mild honing .... will the rings seat and bring the compression up to where it should be or is it way too low to start (90PSI).

Sorry bout all the questions but i'd love to get this old beast back running the way it should be!!

Guess i shouldn't have chucked the rings as well in case it was an over sized piston.

Cheers!!

1. New jug gaskets aren't hard to make or to find, but you'll probably get away with having used the old one. Checking the squish would tell you if you can just eliminate the gasket.

2. A vacuum test would be a good idea (plenty of info. on this site), but that isn't related to your compression.

3. New rings don't have a top or bottom, if they're the thin rings. Thick rings typically do.
You don't likely have an over-size piston; any P60 piston that I know of would have the same diameter as any other (unlike the A and B, etc. pistons for some saws).

4. The other guys already told you about the de-comp.

5. Your compression should get better as the rings seat. But here's the thing: Thin-ring Pioneers can show alarmingly low compression and still run like a turpentine cat. According to Timberdollars and others, the thin-ring pistons build compression as they run. Kinda makes sense to me.

Someone else may chime in and correct any of the above, and I'll learn something as well.

You may not have a problem at all. Interested, though, to hear how she runs after you get some time on her.

Hillwilliam

 

[StihlNAlberta]

Id would firstly like to say thanks to all who replied. Some great info and tips!

So today I was able to spend a little time with the saw with some of the tips given in the reply's. Decompression valves can leak, WD 40 trick, not to re-use base gaskets, pinning rings, cylinder honing good/bad, vacuum test not really causing low decompression, seating rings.

Well given that there was a pretty fair amount of scoring in the jug, I asked the Stihl fellow to just touch it up as best he could and he told me he wouldn't take too much off. I didn't take any pics unfortunately before I put things back together. He used a 3 prong hone from what I understand, all because I haven't had much luck finding a top end through e-bay or acresinternet contacts, etc.

Before I started these tests I had a compression reading of 90PSI. The night before I removed the old decompression valve and sealed it closed with ultra copper as living in a small town sometimes small fine thread bolts are not easy last minute. Re-installed and checked compression - it came up to 105PSI. I then coated the top of the piston with some WD40 and re-checked compression - 105PSI. I figured I would try and start it up as I figured these skinny rings should be in the right side up, and after a shot of fuel down the carb and a half a dozen pulls it fired right up!! With a few carb adjustments for idle, it seemed to idle great. Didn't run it too long as I am still waiting for my 32" Cannon.

So there it is. I guess next I will need to try a tank or two to see how the power is once the bar arrives and go from there and hope that these saws do run on that general sort of compression or with the rings seating the compression may smarten up a bit.

If anyone else has info on the P60 it would be great!!

Thanks again!!

 

[Arrowhead]

Proper honing will not ruin a cylinder. I've saved several lightly scored jugs by properly honing them, and gained 50+ lbs. The problem with honing is most people don't know what they are doing. The proper hone, proper oil, proper speed....etc.

It sounds like your dealing with a scored jug. Max comp on a P60 is 150. At 120 they will run fantastic being a reed saw. Your saw will gain some comp. after a few tanks. If it's been sitting awhile, I'd put some new seals in it. They are easy to find and easy to change. There was a reason for the scoring in the first place. Another common place for an airleak on a P60 is between the block and reed cage.