piston to valve clearance, why static???

[aigel]

I am reading the rebuild book and am at the piston to valve clearance check section.

Why do you have to do this static? Why don't you just set the 2mm / 1.5mm clearance on the respective valves and turn the engine over very carefully. If there is no obstruction, you are clear.

Especially if you expect no clearance problems since you had no machining etc. but just want a sanity check, I feel that the static method in the book may be overkill / a waste of time?

TIA,

George

[Ho Hum 74]

Why don't you just set the 2mm / 1.5mm clearance on the respective valves

What do you mean by this? I'm not convinced you can just "set" it.

But I was thinking that in the case of a non-modified motor you could just set the crank to TDC for overlapping valves and take measurements at increments of 5 and 10 degrees before and after. You should be clear.

Tristan

[Tim Walsh]

I did this on my motor.. sort of. If you set it to the full 2mm and DON"T clear by a fair amount what's going to happen to your valves? I set my lash to 0 then went one half more turns in (0.5mm) and turned the motor over SLOWLY. then @ 1.0 and then at 1.5 then at 2.0.

[dtw]

Originally posted by aigel
I am reading the rebuild book and am at the piston to valve clearance check section.

Why do you have to do this static? Why don't you just set the 2mm / 1.5mm clearance on the respective valves and turn the engine over very carefully. If there is no obstruction, you are clear.

Especially if you expect no clearance problems since you had no machining etc. but just want a sanity check, I feel that the static method in the book may be overkill / a waste of time?

TIA,

George

That is exactly what Bruce Anderson told me to do. However, he suggested working up to the clearance in increments just to be safe. This worked like a charm for me - I did it the "last" time I timed my engine after using the Wayne method (which was a huge pain in the ass but definitely 'safer' which is why I imagine he prescribed it in the book) the first time around. For that matter, Bruce also mentioned that 1.5mm for a minimum exhaust clearance would be fine, contrary to the Wayne book which prescribes 2.0mm. Actually part of our email exchange was published in Excellence earlier this year as a tech question - flip back a few issues and you should see it.

We also used Bruce's method exclusively when timing Tim's engine.

[aigel]

Tristan:

If you push in the valves with the set screw to 2.0mm / 1.5mm respectively, you will see if there is a clearance problem when you turn the engine. You basically know that there is more than 2mm/1.5mm clearance at all times, once the valves are set at zero / 0.1mm lash.

Dave:

Let's see if Wayne chimes in. Of course Wayne knows the 'dynamic' method. I guess he purposely recommends the static procedure since you really don't want to hit the valves, even turningthe enigne by hand. Depending on the shape of the piston, the valves get hit at a rather steep angle and may take harm.

Again, if you are 99% sure that you have good clearance, (e.g. you are assembling all your old non machined components) and if you are very careful turning, the dynamic method should be fine as a sanity check. One may also combine both methods.

One other method you can do, if you have to dry-assemble and then dissassemble things anyway, is putty, like the pushrod V8 crowd uses it. Just put the putty on top of the piston, time cams, set valves to spec. turn engine over a few times. Disassemble and measure minimum thickness of the putty. That method will give good info on where to machine, if you need it.

George

[dtw]

I had some friends who built a pretty insane race motor - they couldn't get good readings with "play-do" (brings back memories). Apparently it would stick to the head and piston and sorta tear apart. They ended up blowing the lead out of some solder and using that. I remember reading something about some special putty you can use just for that, which won't tear or deform. I agree, there's plenty of good and resourceful ways to skin the clearancing cat.

[Ho Hum 74]

If you push in the valves with the set screw to 2.0mm / 1.5mm respectively, you will see if there is a clearance problem when you turn the engine.

I think I understand what you are saying. Let me repeat back what I heard:

At TDC (where you adjust the valves), instead of using a feeler gauge, you use a dial gauge to dial in 2mm (or 1.5mm depending on the valve). Then you turn the engine over. The theory being that at it's worst case there should still be enough clearance to turn the engine.

Sounds pretty good, I'll give it a try.

Tristan

[dtw]

Originally posted by Ho Hum 74
I think I understand what you are saying. Let me repeat back what I heard:

At TDC (where you adjust the valves), instead of using a feeler gauge, you use a dial gauge to dial in 2mm (or 1.5mm depending on the valve). Then you turn the engine over. The theory being that at it's worst case there should still be enough clearance to turn the engine.

Sounds pretty good, I'll give it a try.

Tristan

Not quite - you can't turn the screw down with a dial gauge in the way. However, the thread pitch of the adjuster screw is 1mm; ie, a 360 degree turn of the screw will result in 1mm of travel. So, you can use this as a guide in determining how far to turn the screw down. If I was dealing with a modified engine, I wouldn't start out right at 1.5mm, I'd work up to it from 0.0mm of pre-lift.

On my high-compression motor, I did hit resistance at a certain measurement. Be sure to turn the motor over super-duper slowly and carefully when you are coming on and going off cam.

[echrisconnor]

At the very end of Wayne's description of this procedure he basically says you can do the dynamic method as a shortcut.

Ho Hum. You don't need a dial indicator. Read Wayne's description. The thread pitich of the screws is 1.mm. Turn the screw 720 degrees and you've dropped it down 2mm.

Edit: (posted at the same time as DTW)

[aigel]

Originally posted by echrisconnor
At the very end of Wayne's description of this procedure he basically says you can do the dynamic method as a shortcut.

Doh - I missed that!

George

[Wayne 962]

Originally posted by echrisconnor
At the very end of Wayne's description of this procedure he basically says you can do the dynamic method as a shortcut.

Yes, I added that at the end. I had some heated discussions with some people who helped me with the book about the probability that people would mash their valves and pistons together while doing this check.

Yes, for CIS/Motronic engines with plenty of clearance, then the shortcut should work fine with no problems. On race engines, or early carb/MFI engines, you should proceed very carefully.

-Wayne