Ts410, sorry another

[adw]

I have, and use a leak down tester, but only on four stroke engines, as spud says it will not really work on a two stroke.

[Mike the builder]

Part 2. New piston and rings fitted to new cylinder. I now get compression with my (wrong) tester of 135psi. So that’s 30 psi better over several good pulls. 
just for fun I tested the old piston rings as described earlier and I get a gap of 13 thou top middle and bottom of the bore with both rings. Pretty consistent. 13 thou good ?

ive noticed the new cylinder is harder to pull over although this is to be expected with 30psi improvement in compression ?
the new rings are quite a lot stiffer and more tricky to fit to the new piston, again to be expected. 
I had a good look inside with a torch and couldn’t notice any worn out sections although it would be fair to say I’m not 100% what in looking for and I tried to get a gauge between the piston and the bore in several places and was unsuccessful. 

[spudulike]

13 thou is OK and should give reasonable compression.

 

[adw]

Just about to say the same, can’t imagine why it had so little compression, is the deco valve leaking?

[spudulike]

Just checked the pics to see if the piston crown has been cracked...common when solid screw in piston stops have been used but it looks clean. 

I reckon the issue is with the compression tester. It looks like the valve in it may be close to the top of the gauge so the tube going up to the actual gauge is forming part of the combustion chamber lowering the reading.

You lose so much when you can't pull the engine over to feel what it has on the recoil handle!

 

[peatff]

12 hours ago, adw said:

Just about to say the same, can’t imagine why it had so little compression, is the deco valve leaking?

 

He tested it via the decomp hole so it can't be that.

[bmp01]

Presume new piston/cylinder was assembled with oil on rings,  when you did the part 2 compression test ? Did the original piston/cylinder get tested under the same conditions? That could well be the increase in compression you're seeing. 

Yes the increased compression will make it harder to pull over,  along with the higher tension on the rings on the 'rough' cylinder bore. It will take a little running for the rings to polish the cylinder bore and I guess the rings will get heat treated and loose some tension with running. Any oil from the engine  build will get burnt off early doors , expect a drop in compression. Maybe a slight increase with time as rings bed in.

 

Edited October 13, 2021 by bmp01

[ChrisNewport]

It'll be carb trouble, always is with these saws when the p and c is clean.

[bmp01]

12 hours ago, spudulike said:

I reckon the issue is with the compression tester. It looks like the valve in it may be close to the top of the gauge so the tube going up to the actual gauge is forming part of the combustion chamber lowering the reading.

That's definitely true, valve is up near gauge. If the same comp tester was used on a running 2 stroke engine we'd have the low compression numbers confirmed.

 

[bmp01]

6 minutes ago, ChrisNewport said:

It'll be carb trouble, always is with these saws when the p and c is clean.

Although I had one where the ignition lead was pinched in the casing at the factory. Made a pin hole in the ignition lead where it had arc'd through.