Checking valve to valve clearance

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Ozonkiller
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Checking valve to valve clearance

Post by Ozonkiller » Fri Aug 11, 2017 2:19 am

I know that this must have been covered but damned if I can find it...

How are you guys checking valve to valve clearance during overlap on a twin cam, four valve engine.
Valve to piston is easy peazy but I'm upping the ante with bigger cams with more overlap with oversized valves...

Thanks,

Tom

4vpc
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Re: Checking valve to valve clearance

Post by 4vpc » Fri Aug 11, 2017 3:40 am

Turn it over, open valves and measure gap.

hoodeng
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Re: Checking valve to valve clearance

Post by hoodeng » Fri Aug 11, 2017 4:21 am

I am presuming you are doing a mock up before you bolt the engine together? The cam manufacturer should be able to give net TDC lifts for all valves , mock the head up on the bench and drop the valves the prescribed amount and you will see what the TDC clearance is ,if .080" valve to valve is recommended minimum ,you would want to measure and confirm you have what is required.Grease on the stem helps hold settings.
Take the opportunity at this time to dry run the head on the engine without springs to confirm valve to piston clearances and valve to pocket radial clearances , setting the head up as it would be in final assy including head gasket or spacers to the equivalent .Slip an o ring over the valves to retain.
Record everything that you measure on a cutaway drawing or you may already have a build sheet system that tracks your processes , it makes the job easier to come back to if you don't get a clear run from start to finish, and a reference for re work.
Do not bolt an untried valve train {or any untried assy} together and bar the engine over hoping to pick up the hits and misses , you may find yourself investing in another set of parts.

Cheers.

Cubic_Cleveland
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Re: Checking valve to valve clearance

Post by Cubic_Cleveland » Fri Aug 11, 2017 7:56 am

hoodeng wrote:I am presuming you are doing a mock up before you bolt the engine together? The cam manufacturer should be able to give net TDC lifts for all valves , mock the head up on the bench and drop the valves the prescribed amount and you will see what the TDC clearance is ,if .080" valve to valve is recommended minimum ,you would want to measure and confirm you have what is required.Grease on the stem helps hold settings.
Take the opportunity at this time to dry run the head on the engine without springs to confirm valve to piston clearances and valve to pocket radial clearances , setting the head up as it would be in final assy including head gasket or spacers to the equivalent .Slip an o ring over the valves to retain.
Record everything that you measure on a cutaway drawing or you may already have a build sheet system that tracks your processes , it makes the job easier to come back to if you don't get a clear run from start to finish, and a reference for re work.
Do not bolt an untried valve train {or any untried assy} together and bar the engine over hoping to pick up the hits and misses , you may find yourself investing in another set of parts.

Cheers.
O-ring is a great idea, thanks!

jsachs1
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Re: Checking valve to valve clearance

Post by jsachs1 » Sun Aug 13, 2017 4:45 pm

What I do is:
Open exhaust valve to cam spec. tdc overlap lift. Then open and close intake valve, and check clearance at the closest point.
I use carb slide springs on the valves, and my flow bench valve opening tool. :wink:
John

Ozonkiller
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Re: Checking valve to valve clearance

Post by Ozonkiller » Tue Aug 15, 2017 1:53 am

Thanks for the input.
I definitely check EVERYTHING when building my engines. That's why I'm asking. I've tried a variety of methods but I've always got that nagging, "is the light really turning off when I close the refrigerator door?" feeling.
This specific build involves oversized valves AND cams with more duration. My plan is to mock up and plot the valve positions during the overlap. I can also see all of the intake valve through the port so with some probing with solder I should be able to verify...
Also, this evening, I realized that the valves need to be at around .390" lift to hit. I'm running .420/.400" lift intake/exhaust. Taint, no way I'm near that during overlap... I hope. That's why I'm checking.
Again, thanks for the ideas and input

Tom

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