[Vytas]

Hi Guys,

I have a 2L rebuilt engine that i have put into my GTV. After many evenings trying to start the engine, and fiddling with carbs, distributor, fuel pump and trying just about everything i broke down and took the car to my Mechanic. We did a compression test and it turns out that 1 and 2 cyclinders have no compression, while 3 and 4 have the proper amount. We took the cam cover off and everything seemed to be on TDC and the lobes facing out. What could be the problem? Cams? bent valves?
I didn't build this engine, so i am not entirely sure if everything was done properly.


Thanks

 

[pc77]

In order to have compression, you need to have both valves closed, and properly sealing rings. Have you tried a leak down test? Bring the piston in question at TDC compression/power stroke (both valves closed and lobes pointing out). Make sure you keep the engine from turning. With the leak down tester put 90-100 PSI air into the cylinder. The second gauge on the tester should read no more than 5-10% less than the first gauge. (for example if you put 100 psi on the first gauge, the second gauge should read 90-95 psi). If you have a reading of, say, 60-80, something is definitely wrong. At this point listen for leakage noise. Noise in the intake = intake valve problem, in the exhaust = exhaust valve problem, in the oil pan (open the oil fill cap) = rings. It's possible that the rings may have been installed backwards, or that you have a bent valve or two.

 

[Vytas]

Thanks Pc77 for the write up. I will give these suggestion a shot.

 

[genericwood]

If you truly have zero compression in a cylinder, you almost certainly have bent/stuck valves. Improperly installed rings would yield low compression, but unlikely no compression.

 

[60sRacer]

Cam timing error could do this too, by holding a valve open. It's not that hard to put the cam in 180 degrees out.

Robert

 

[Vytas]

I have a compression reading between 40 and 50 in 1 and 2 cylinder, and a reading of 140 for 3 and 4. Thanks for the response guys. I'll do some further investigating tonight.

 

[classicalfas]

Also check your valve clearance. Make sure there is some type of clearance between the cam and the follower.

 

[gigem75]

140 on a fresh engine seems low