If your pulling the engine over until the compression stops going up, you likely have a bad compression gauge. How does the compression feel? try testing the gauge on a another saw and see what you get.
Ms661 falling while in the cut
- Thread starter Matt Schmitt
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I did my 461 it had 165.
I haven’t got the saw back it’s still at the shop.
Rick Stephens
ArboristSite Operative
Get it running and go burn a couple tanks through it. You're fine at 130 with fresh piston ring job. Go to working it and don't worry.
Sounds good
?? It should have well north of 150psi period.
By all means run it and re check. Did you use some assembly lube when installing the piston and cylinder? If yes that will actually falsely raise compression, which is the main reason you want to run the saw and let it cool down before checking compression after a fresh rebuild. 130 is really low for that saw.
Ok I did use a little oil, once I get it back and make some cuts I’ll recheck it.
Rick Stephens
ArboristSite Operative
Until he runs it and breaks the rings in, initial compression numbers are pretty much meaningless. It's going to go up. Stop worrying and go to cutting. The assembly is done. Time to put it to work.
Out of All the saws I or anyone else I know have rebuilt, ported and re ringed, I've never seen compression jump more than 5psi after break in. 130psi is far too low for a 661, something is off if it's that low.
The only thing I could think left would be a worn out cylinder rings were set properly it was vacuum pressure tested.
Rick Stephens
ArboristSite Operative
Point is: Choices are, 1) start over, tear it down, mike the rings, replace the cylinder etc. 2) run it and see what you got.
I don't quite get what you are saying. The rings and piston are new, right? The bore looks pretty good. The end gap on the new rings is acceptable and the rings fit the piston? No leaky compression release?
Your choices are still, run it and see how it does or tear it back down and see what you can see with a second look over. Andre may very well be right and there is a problem you should find. But if you were careful in your assembly and checked fit, I don't see a downside to running it and seeing how it does. The rings and piston are already used at this point.
I believe he still has gauge issue, larg saws can blow the o-ring an give low reading, the only compression gauge that I found to work consistently is snap on.
I’m using a Bosch that is less than a year old and it seems to work fine on my 461 it could very well be blowing the ring but I just think it is. odd that it does fine on my 461. Also on a vacuum pressure test Wouldn’t that detect a leak in the decomp?
It should unless it only leaking under pressure, which is not likely, dcomps normally leak under vacume.
All right do you not think the odds of the coating being worn too much on the cylinder is a possibility?
You'd see pealing of the coating.
You could try checking squish. You did use the correct size rings?
Got it back today seems to run pretty well maybe a little lack of power but I didn’t cut but a few cuts.i asked about the spark he said its was making spark the whole time its just really hard to see I guess. I’ll run it this weekend and see how she does.
