3CL Compression

[ghwallice]

My 3Cl was fitted with 10.5:1 pistons and 4C cams 30 years ago. Don't think the head has been off since. What sort of psi should I be looking at on a compression guage, and what sort of variance is acceptable?

Regards, Greg

 

[Paul Marx]

Has it been used in 30 years?

Paul

 

[ghwallice]

Yes, I've done about 7000klm on it over the last 7 years.

 

[Gerald]

Hi Greg,

IIRC you should see something like 170 PSI and all readings close to each other.

HTH
Gerald

 

[Grant]

Can be subjective due to differences in equipment used, but anything over 150psi is usual, plus consistency between cylinders is the key.
Make sure all valve clearances are correct before doing the test.
If any cylinder is lower than the others try putting a squirt of oil down the plug hole and trying again.
This shows if the rings/bores are to blame.

 

[Vince]

Throttle fully open during the test.

 

[Dellortoman]

Compression will vary depending on what cams are fitted (inlet valve closes after bottom dead centre on compression stroke)
A11 cams close the inlet valve later than 4C, so compression will be lower.

 

[ghwallice]

Running 170/180/170.

Still tuned for 108, and is running rich on 98, But::::::

I ride it for 3000klm, and oil has just a slight touch of black. Craig rides it 640, yes, 640klm, and oil is as black as diesel oil. WTF???

 

[Cosi]

Running 170/180/170.

Craig rides it 640, yes, 640klm, and oil is as black as diesel oil. WTF???

Craig is riding it properly...

 

[ghwallice]

Craig is riding it properly...

I was waiting for you to comment!! True to form...