Hi guys,
i am brainstorming why my engine is having very low compression of around 10 psi. I have yet to take a look at the insides, but was thinking is it possible that the starter is cranking too slowly and pressure doesn't build up?
I am guilty of running the starter for way longer than the recommended 5 seconds, maybe a full minute at some point. Would that ruin the starter all at once or would it get slower? at what rpm should the engine be cranking with a good starter?
thanks a lot!
Wow. 10psi? There's something else going on. A couple things, actually.
With the spark plugs out, the starter motor should spin the motor over fairly easily. If it's barely turning over, than your starter motor needs rebuilt / battery is dead / bad wiring somewhere / etc.
As far as the low compression goes, I would immediately guess your valves need attention. Or the piston rings are shot. Or.....the throttle isn't open at all. Start with why the starter is so slow, then work up to your compression problem.
Quote from: sashkar2000 on July 26, 2013, 11:26:53 PM
Hi guys,
i am brainstorming why my engine is having very low compression of around 10 psi. I have yet to take a look at the insides, but was thinking is it possible that the starter is cranking too slowly and pressure doesn't build up?
I am guilty of running the starter for way longer than the recommended 5 seconds, maybe a full minute at some point. Would that ruin the starter all at once or would it get slower? at what rpm should the engine be cranking with a good starter?
thanks a lot!
tight valves= low compression.
slow starter= less air squished.
slow starter = less chance of an sub optimal air:fuel ratio igniting.
hard for me to say what is good cranking, would you say the intake valve should move up and down about once a second, or much more often?
Did you hold the throttle wide open during the Comp Test? Not doing so will give you a low reading.
i had the carbs off during the test. got another thread describing how i got into this mess, bit was hoping to rule out the starter before opening up the engine.
Quote from: ohgood on July 27, 2013, 06:11:48 AMslow starter= less air squished
The speed of the starter should not significantly affect compression, so long as the valves and rings are in good working order. Compression is not a function of engine speed.
Did you check the valves yet? I'm pretty sure there's a whole mess of us back in the other thread saying to check the valves lol.