Valve gap on an unknown camshaft?

[old31]

On a standard 30/31 engine without knowing what you have for a camshaft what would you gap the valves at?

[Will N]

I'd go .015". Better too big a gap than too small.

[redmodelt]

Don't think what cam shaft you have in the engine matters(?). Gap is gap and valve expansion rate has more to do with it. Cold I would go with .012 intakes and .012-.015 on the exhaust. As long as the toe has equal wear across all the lobs, the engine should run pretty even.

[Dave in MN]

I have been running newly rebuilt engines, fitted with stainless modern valves, on my dyno for break-in and have noted that when running them full out near the end of the break-in period, the exhaust valves may need .015". The engines develop lots of heat during these final runs and the exhaust valves may not seal due to expansion of the stems. It's very clear when the exhaust valve(s) stop sealing as the engine rpm severely drops suddenly.
Based on what I have observed, I set the intake valves at .012" and the exhaust at .014 for an engine that will be used as most of us use them, moderately. For those that like to run faster, I set them at .013" and .015". My take on it anyway!
Good Day!

[40 Deluxe]

Camshaft lobe design does enter in here. Solid lifter cams have opening 'ramps' (slow and gentle) to take up the clearance before actually opening the valve. If the clearance is excessive the lifter will miss this ramp and slam directly into the lobe. This results in noise and extra wear. You can see this with a degree wheel and dial indicator.

[old31]

Sponsored Links (Register now to hide all advertisements)

Dave, I do go faster so 13 and 15 Sounds good to me.

You mentioned brake in period. What should the brake in period be for new rings and refreshed valves?

[Jim Brierley]

Originally Posted by redmodelt

Don't think what cam shaft you have in the engine matters(?). Gap is gap and valve expansion rate has more to do with it. Cold I would go with .010 intakes and .012-.015 on the exhaust. As long as the toe has equal wear across all the lobs, the engine should run pretty even.

In performance cams it can make a big difference! Winfield cams for instance were set very close, .010" was very common. Isky cams were often set at .030".

If your cam has not been ground, I would go with .012" and .014". Compare your cam with a known stock cam to see. Look at the amount of material that the base of the lobe extends above the core of the cam will give you an idea.

[nkaminar]

Turn the engine over to measure the clearance at different positions of the cam. Start with the cam at the heal (follow rule of 9). Turn the crankshaft 20 degrees which is 10 degrees at the cam and measure the clearance. Repeat for each 10 degrees of the cam. Using this method you can determine how accurate the cam was ground and if you have a ramp before the valve opens. Start with 0.012 clearance at the heal. If the cam was reground it can be all over the place depending on how good the shop was and what profile they were using. While doing this you can check how many degrees the intake and exhaust valves are open. Usually the open duration was quoted at at certain valve openings, such as 0.020 inch, not when they first start to move.

A method used for Model T's was to set the clearance so that the valve opening degrees were identical for all intake and all exhaust valves. The position of the piston was used as a measure of valve timing. The engine was turned over until the valve just opened and the piston depth was measured. The clearances were set so that the piston position was identical for all intake and all exhaust valve openings. Piston positions for intake and exhaust valves were different.

[katy]

Originally Posted by Dave in MN

I have been running newly rebuilt engines, fitted with stainless modern valves, on my dyno for break-in and have noted that when running them full out near the end of the break-in period, the exhaust valves may need .015". The engines develop lots of heat during these final runs and the exhaust valves may not seal due to expansion of the stems. It's very clear when the exhaust valve(s) stop sealing as the engine rpm severely drops suddenly.
Based on what I have observed, I set the intake valves at .012" and the exhaust at .014 for an engine that will be used as most of us use them, moderately. For those that like to run faster, I set them at .013" and .015". My take on it anyway!
Good Day!

When " running them full out near the end of the break-in period," do you have a load on the engines?

[Dave in MN]

Originally Posted by katy

When " running them full out near the end of the break-in period," do you have a load on the engines?

Yes, fully loaded with the dyno to determine the rpm the max torque is produced and the max horsepower of the engine.

it requires about 2 hours of running with various loads applied by the dyno before I feel comfortable completing a full load "pull".

[Bob Bidonde]

Thanks Dave for giving us some real world experience regarding valve clearances. I like that you dyno test & tune your engines. Do you have a business website?

[jack backer]

One thing to consider with lash is valve life, an exhaust valve cools when it’s closed. There is a balance between valve life and performance.

[katy]

Originally Posted by Dave in MN

Yes, fully loaded with the dyno to determine the rpm the max torque is produced and the max horsepower of the engine.

it requires about 2 hours of running with various loads applied by the dyno before I feel comfortable completing a full load "pull".

Thanks, smiles,

[motordr]

What clearances would you set a new old stock Model B cam valves at? Go with ford specs or what have you found works for you? Or just regrind the NOS cam to a more up to date pattern?

[jack backer]

Originally Posted by motordr

What clearances would you set a new old stock Model B cam valves at? Go with ford specs or what have you found works for you? Or just regrind the NOS cam to a more up to date pattern?

Measure tha B cam, late model B’s were high lift, as good as it gets

[Jim Brierley]

Ford made 3 different B grinds, I assume each change was chronical? first .305", then .315" and then .339". The .339" makes a great touring cam, especially when other mild mods are incorporated.

[Patrick L.]

Ford changed the exhaust lash spec for the B cam to .022" because of burnt valve issues. However I don't know exactly when that happened and if it referred to a particular shaft.