New Piston & Cyl Kit - Low Comp

[theoldfox]

I have an 026. It was a sec hand saw and when got it had a scored cylinder. So it had a new piston and cylinder kit put on it (Baileys 026/Ms260 kit).

The saw starts, idles and cuts ok, but seemed to be lacking a bit of power. After about an hours use I have compression tested it...... 60 psi!!!! (dry).

I pulled the head back off and checked nothing had gone a miss, but all seems good. I gave the bore a slight hone and put back together, still 60.

I then did a wet test and comp increased to about 110.

The saw is an old model 026 (black airfilter). The new cylinder has been fitted with the std base gasket.

Does it take a while for new rings to bed in?? What should the comp be for a new P&c kit after an hours use ??

Is there a difference in stroke between the new models that might be causing this?? Should I remove the base gasket and just use a high temp sealant??

Appreciate any advise

Cheers

 

[AUSSIE1]

Try measuring your squish with and with out base gasket. Around .018-020 is a good figure to aim for with most saws of this size.

Check ring end gap in cyl. to see if spec is too large.

 

[AUSSIE1]

Another thought.
Does that saw run a decompressor?
They are known to leak.

 

[sloch24]

Somethings not right with your test. A saw that's only making 60PSI will not run. Make sure that your compression gauge is okay (try it out in a known good saw, or use an air compressor).

I dunno.. something isn't right..

 

[Mad Professor]

You should have got an OEM 026 stihl kit from the member here, who is selling for less than the Bailey's kits.

 

[blsnelling]

Like was already said, the saw wouldn't run with only 60 PSI compression. Any other discussion is a moot point.

 

[wheelman]

Somethings not right with your test. A saw that's only making 60PSI will not run. Make sure that your compression gauge is okay (try it out in a known good saw, or use an air compressor).

I dunno.. something isn't right..

:agree2:

 

[AUSSIE1]

Like was already said, the saw wouldn't run with only 60 PSI compression. Any other discussion is a moot point.

Yeah considered, but he did say it's low on power.
Could have an issue with his gauge also.

 

[E.V.A. Sawman]

I recently purchased a p&c kit from baileys for a 036. Noticed the the combustion chamber area was not finished like o.e.m. round, but more of a light bulb shape. Checked ring gap, squish, etc. all OK. Saw started fine, let it run through a couple break in cycles. Checked comp. about 115. Used another gage same. took apart rings were starting to seat fine. Called baileys, they sent new p&c,(no charge) on this one, combustion chamber was very good, perfect circle. Did all checks, all good, put together, ran few break in cycles, now 145lbs. comp. most likely will get better with run time. Another note, tried to get a 036 pro gasket from stihl, they are 1/2 m.m. thinner than regular 036. they are different part no. but the gaskets are the same thickness. had stihl dist. order again, still same gasket in different bag. They tried to find out what is up so far have not gotten answer back from stihl.
With out gasket squish clearance will be very tight or over. Compression would probably be a tad higher with thinner gasket.

 

[Taxmantoo]

If it was purchased as a kit, the piston windows would have to be a match for the transfer ports, yes?

 

[theoldfox]

New P&C kit

I tried the gauge on another 026 and a newish smaller saw, both gave 150 readings so figured gauge was fine.

I agree, this saw starts and runs far too well for 60 psi but thats what the gauge consistantly tells me!!!

It must be one of those frustrating mysteries!!!!!

 

[stihlboy]

1:did you re-tune the saw after putting in the p&c?

2:did you keep from free revving the saw immediately after putting it together?

3:did you lube the piston and rings when you assembled the kit?

4:have you ran the saw carefully since assembling it?

5:did you make for sure the piston was put in facing the right direction??

failure to do one or more of these can and may harm your saw....

just for the sake of sanity pull your muffler and post pics.

thank you

 

[woodyman]

Did you put the piston and rings on the right way?

 

[ironman_gq]

check the ring end gap on the rings and measure the piston and cylinder to see what the clearances are. you may have a large end gap or your piston and cylinder may have been machined wrong

 

[AKDriveSprocket]

Looks like the bottom ring is up side down.

 

[litefoot]

Does it take a while for new rings to bed in?? (Answer: Around 10 tanks of fuel.)What should the comp be for a new P&c kit after an hours use ??(Answer: Greater than 150 psi)

Is there a difference in stroke between the new models that might be causing this?? (Answer: No, the 44 and 44.7mm piston and cylinders share the same stroke,) Should I remove the base gasket and just use a high temp sealant??(Answer: No, as has been suggested, recheck your comp tester.)

Appreciate any advise

Cheers

 

[wigglesworth]

Looks like the bottom ring is up side down.

Yep, better check things out more carefully.

 

[HimWill]

Those pictures weren't posted by theoldfox,Woody posted them.

 

[Evan]

you guys have better eyese then I I for sure cant tell if the bottom ring is upside down

 

[AUSSIE1]

Lower ring groove. See the pin?
The ring end to the left of the pin.