Well if it is reading around 160 in good saws it is good.
Looks like the machine marks are still on it, I don't think it's very worn at all upon first glance. So this one uses a small plug what plug size do the other saws with more compression readings have, did you need an adapter for the saw you are working on because that would explain it. If all things are equal, it doesn't make sense.
Yes, no wear, not even dirty. Yes, had to use a small adaptor on the 171, not on the 170/180, but they only read 125. The 171 read 125 with oil - I know it should be dry - the other two and the 361 were. I'll check the opening on the adaptor and compare to the regular fitting. If it's much smaller, then try to restrict the regular fitting to see if it makes a difference.
The adapter can give low readings. I wouldn't worry about it from the looks of that piston. I'm thinking once you properly fix the leak, it will run. What was the cause of the leak again?
Sounds good to me.
Thanks. How many tanks of fuel has it run? How man pulls and what gauge did you use? Never mind - I see it's a Mityvac.
The leak was my fault - didn't seal the upper intake port well enough. That wouldn't affect compression as both ports are open during compression test. When I pulled the engine, I made a plate to cover all three openings on the block. With the mounting bolts installed in the bottom clamshell, no leaks. I don't see how a leak on the bottom end would affect compression. I've had saw with leaks still have good compression. I could see iIf it was a leak on the top end, but then it wouldn't hold pressure. I'm plugging off the exhaust and intake, including the impulse port and testing through the spark plug hole.
That makes the most sense so far. The 171 has a smaller spark plug hole, see photo of adaptors I bought, it takes the smallest one in the set. So, the schrader valve is back a ways, effectively increasing the size of the combustion chamber. This would have a more effect on smaller cc engines and reduce compression readings. On the 170 and 180, no adaptor is used so the schrader valve is right in the chamber and reading are higher. Lone Wolf, this is probably what you were trying to tell me earlier - sorry it just didn't click at the time. Mea Maxima culpa. So, I will attempt to measure the amount of increase caused by the adaptor and compare it to the 170/180. I'll fill the space in the adaptor with water when installed on my tester and compare to the cc of the combustion chamber. The percentage of increase is probably equal to the drop in pressure between the 171 and 180. I may attempt to machine my own adaptor so the valve is farther into the spark plug hole. I will also let the company that makes the adaptors know to take the increase into consideration and advise customers.
. I took an old rubber tire valve and stripped off the rubber, measured the brass, and bored out the adapter, then machined the tire valve to a snug fit and assembled with red loctite. The shrader valve is now as close to the compression chamber as I can get. I did use the schrader valve from my tester, not the tire valve. I applied pressure to the other end of the tester hose and no leaks. I will assemble the saw with the broken parts and retest compression. Assuming this works, I will notify the adapter company.FWIW, DO NOT use regular tire schrader valves. You need a special one with low spring tension as the pressure to open the valve will effectively get SUBTRACTED from your reading on the gauge.Here's my solution. First pic shows the relationship of my tester to the adapter
You are correct. As stated in my post, I didn't use the tire valve shrader - I used the one from the tester. I made it bold now so all can see.
