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Old 10-06-2012, 01:00 AM
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Quote:
Originally Posted by gfackrell View Post
Can a SBC run with the cam timing off? What would the symptoms be, and how can I test to see if that's my problem?

I will quickly detail my situation.
installeda '79 350 rebuilt engine in my boat. put all the original external parts back on it. Carb, distributor, alternator, etc. It's an old points style distributor, and I'm pretty sure I timed it correctly.8* btdc at idle. Spec from the oem manual.
I am not getting good power, and my compression is strangly low on all cylinders. I have re adjusted all valves to make sure they aren't too tight, and still getting low compression.
Compression is as follows:
1-112
2-119
3-99
4-109
5-105
6-100
7-89
8-107

This engine has 23 hours on it, it starts pretty well, and runs fine. Just underpowered.

I read a post where someone thought this was their problem but wasn't. A guy said that with the cam specs and a dial indicator you could check to see if the cam was lined up with the crank. I would like to find out how to do that if possible, before I pull the front cover off to visually check. Can anyone help me with this?
You know for a fact this engine had low hours and was rebuilt correctly in the first place? I ask because w/low compression (assuming the gauge is correct) but not uniformly low, it looks just like a worn/high hours engine might look.

An engine w/retarded cam timing might have lower than normal compression if the amount of retard was enough- but you'd also expect the compression to be a lot closer from cylinder to cylinder on a fresh engine.

But then you say there's no increase in compression w/oil added to the cylinder. The oil should be shot to the top of the cylinder to get the best result. If the oil was sufficient for testing (a couple teaspoons worth is enough) and no increase was seen, this points to a loss of compression due to valve seal.

A leakdown test is the next thing I would do. If you have the ability to pressurize a cylinder at TDC compression stroke, you can listen for a loss of pressure at the carb and/or exhaust (would be valves), or if you hear hissing through the valve cover or breather you could blame the ring seal. This isn't as good as a leakdown test but can point to a problem if it's present.
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