Can you identify big valve head without removal?

[Quart Meg Miles]

You can't easily infer the CR from the compression test for two reasons:

1. The compression will be adiabatic during the test rather than isothermal so the pressure will be higher than expected;

2. Wild cams don't seal the volume of the cylinder until later than milder ones so compress less of the cylinder's contents at cranking speed leading to lower compression figures than expected;

But your compression figures are as high as any I've seen, John!

Another test for a full Sprint conversion is to measure the choke size of the Weber which should be 33 mm for a Sprint while only 30 mm for a standard engine.

[rgh0]

The manual says in excess of 160 psi and all cylinders within 20 psi when tested at a cranking speed of 200 rpm with throttles fully open at sea level. Typically 170 to 180 psi is what I see in a nominally standard engine

How much you head has been skimmed and the thickness of your head gasket with affect this. Carbon build up in the head will also affect it. Valve timing also affects with longer duration cams producing a lower low speed compression pressure.

cheers
Rohan

[stugilmour]

Thanks guys. Given that mine runs fine and I am at roughly 3,500 above sea level I will call it good.

[Johnfm]

So

bearing in mind I have no idea what the previous owners have done, the jetting seems all over the place, the compression ratios are much higher than expected - would the best thing to do be to:

1) pull the cam cover and measure the valve clearance (to make sure it is ok) and measure the cam lift so I can figure out which cam it has; and
2) pull the head, measure the valve sizes and measure the head to see how much it has been skimmed etc


OR

Just put the carbs back on and drive it - get the ignition and carbs tunes and just drive it!

[StressCraxx]

Just put the carbs back on and drive it - get the ignition and carbs tunes and just drive it!

Yes!

[Johnfm]

I think that is the answer!

I will take cam cover off just to check head bolts are torqued properly, check valve clearance is in spec and measure valve lift - so I can identify the cam profile.

I will leave the head on - unless the leaks from the front of the engine are from the head gasket - in which case, I will lift it, check the inlet valve sizes and then seal it back up.

[oldchieft]

Hi All
Just found my compression tester that I have had for more then 40 years.

old gauge with info on it

Close up of small print

This may be a bit of a useful guide.

Jon the Chief

[MickG]

Hi Jon
I've got one of those must be the same age. Still works as well.
Mick G

[Johnfm]

You can't easily infer the CR from the compression test for two reasons:

1. The compression will be adiabatic during the test rather than isothermal so the pressure will be higher than expected;

2. Wild cams don't seal the volume of the cylinder until later than milder ones so compress less of the cylinder's contents at cranking speed leading to lower compression figures than expected;

But your compression figures are as high as any I've seen, John!

Another test for a full Sprint conversion is to measure the choke size of the Weber which should be 33 mm for a Sprint while only 30 mm for a standard engine.

Mine definitely has 30mm chokes.

[oldchieft]

Bit off topic, Hi MickG

Do you or anyone else know were I can get a new rubber cone for my tester?

Jon the Chief