Stock camshaft base circle deviations Options

[technicalninja]

I ran into a problem with my stock 75 1.8L that I thought I should make others aware of.

The base circle of my stock camshaft 31K motor had more than .002" run out.

I figure this out when setting the valve adjustment on my engine.

There are multiple ways of adjusting the valves.

The "Krusty" style where you set the opposing valve (across the engine) at full open and the TDC method are the more common.

Both SHOULD have the same play if the base circle of the camshaft is concentric with the cam centerline.

I did mine Krusty style and then re-checked TDC style. Big difference!
Like as much as .002" difference.

Perplexed, I mapped base circle on all lobes.

I had .002"+ run out on all 4...

The lobes were different offset for the run out as well.
Krusty method OR TDC method did NOT equal same offsets.

All this doesn't mean anything if you are using the stock pushrods that require .006-.008" valve adjustment. That much clearance makes .002 run out insignificant.

But if you're using steel pushrods that require zero you will be doomed!
Burned valves will be the result.

Checking base circle run out is NOT a normal thing to check.
I was NOT planning on doing it...

I adjusted Krusty style and merely re-checked during the leak down test (which has to be FLAWLESS TDC).

My first thought was "Dumb ass got the valve adjustment wrong".
I blamed myself!
Nope, not me, original parts deviation!

Had I not been doing the LD tests at the same time I wouldn't have caught it...

There is more than 360 degrees of "base circle" crankshaft movement in any cam design.

IF YOU ARE USING STEEL PUSHRODS WITH ZERO LASH YOU MUST CHECK THIS!!!!

This could be a "built in" Reaper just waiting to kill your engine!
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[rfinegan]

Great post
I had some issues setting lash and now take the log route and set lobe to max lift and adjust opposite side now on base of lobe to correct lash...then continue to adjust all valves with same process.
Perhaps is best to set on the base circle to the lowest value for each lobe (2x)?Or the base circle opposite the lobe NOT always the lowest spot (run out)? OH my

[Dave_Darling]

Interesting. I had also noticed discrepancies when I compared the two methods, but it was usually handwaved away.

I'm glad I stuck with the "book method" of setting the cylinder at TDC.

--DD

[914werke]

so the question is the recognized discrepancy a baked in manufacturing flaw or result of 50 yrs of wear?

[technicalninja]

Manufacture deviation from my perspective.

The car I have went into hibernation in 1988 at 31k.

It's VIRGIN and very nice.

The DAPOs that bought it first got it running (new progressive carb kit-real Weber) and both its leak downs and compression test (base tests COLD) were the best readings I've ever seen from a 20-year-old set up.
The fact that it is 50 and un-touched" is unbelievable!

In 40 years of doing this stuff this car is the best shape of any "needs resurrection" cars I've ever seen.

Make it SOO much easier if it hasn't been molested...

[technicalninja]

And, after thinking about it...

If the valve adjustment has any play at all (over .0025" for my car!) then the base circle of the cam shaft has no wear...

AT ALL!

[technicalninja]

Great post
I had some issues setting lash and now take the log route and set lobe to max lift and adjust opposite side now on base of lobe to correct lash...then continue to adjust all valves with same process.
Perhaps is best to set on the base circle to the lowest value for each lobe (2x)?Or the base circle opposite the lobe NOT always the lowest spot (run out)? OH my

BINGO!!!!!

That is WHY I mapped all 4.

The deviation was not lobe related. If it was I could have said ONLY Krusty or TDC!

With steel pushrods and the cam I have in my car it appeared to be impossible to set a valve adjustment below .003!

As I'm still on original aluminum pushrods it doesn't matter at all...

But it was an eye-opener to see a deviation of that magnitude on German stuff.

It's the Italian stuff that does shitty things like this...

[technicalninja]

Something I should have added in the first post.

CNC machining has massively improved since my camshaft was cut.

I would expect perfect base circles in modern camshafts.

If you have a modern cam and steel pushrods, I believe the chance of you having a problem with this is nearly zero.

Now, after seeing this crap in mine I do know what I would do at different points in my build.

Brand new camshaft BEFORE installation: Place on V-blocks and check base circle run out and total lift.
You can make V-blocks out of anything hard. Don't have to be fancy here. Oak V-blocks would do in a pinch...

New camshaft installed in case: Using a dial indicator directly on the lifter with a dialed in degree wheel on the crank nose. Base circle run out, valve open and close points (angles) LCA (angle/lift). I'd do this on all 4 cylinders.

I'd "degree the cam" and check lift and run out basically.

Any deviations and I'd be speaking with the camshaft manufacture.




I HIGHLY dislike ZERO lash! (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif)

This gives you ZERO safety cushion for any valve wear at all.
Any wear and you're hanging it open, the valve overheats (if the car still runs), and it burns the crap out of the valve, seat, and maybe the head.

I'd set a zero-lash engine at .001-.002 initially. Run it at least an hour "loose" before going back in and taking lash to zero.

This is ONLY after I did my "full monte" hand lap job on all of the valves.

Fresh from the machine shop (which I NEVER do anymore, they don't get the springs with me) I'd UP those clearance +.002" and run it longer or have two valve adjustments. Run for an hour at .004, tighten to two, run for 10 hours, tighten to zero.

On an engine that is really running zero lash this is the care you have to exhibit.

Now, the zero lash portion of the running is ONLY cold. Once it heats up you should actually have measurable lash. I would expect more than .004" and less than .010".

Has anyone ever verified this?
Checked lash at full operating temp?

I would after that first hour!

[Superhawk996]

I get what you’re saying but even with steel pushrods set at zero clearance (cold) you’re not running at zero clearance when hot so risk of burned valves at operating temp is a lot less then it would appear to be.

The hot lash could be calculated pretty closely based solely on the thermal expansion of the head when hot.

As you stated via leak down, if the lash is jacked up cold, the backfiring at idle is going to be a pretty healthy warning sign.

[VaccaRabite]

I don't see how there could be a difference between TDC or Krusty.

For each method the valve opposite the one you are adjusting is on cam, making it impossible for the adjusting valve to be on cam no matter what version you use.

Or are you saying that your cam itself was wobbling .002 in its bores, and it really didn't matter what version you used?

Back when I had steel pushrods, my "zero" was more like .001 off. I'd roll it in till it just kissed, back off and tighten the nut (knowing the nut was going to tighten the adjuster slightly.)

Did you account for the nut tightening the adjuster a smidge?
Zach

[technicalninja]

I don't see how there could be a difference between TDC or Krusty.

For each method the valve opposite the one you are adjusting is on cam, making it impossible for the adjusting valve to be on cam no matter what version you use.

Or are you saying that your cam itself was wobbling .002 in its bores, and it really didn't matter what version you used?

Back when I had steel pushrods, my "zero" was more like .001 off. I'd roll it in till it just kissed, back off and tighten the nut 9knowing the nut was going to tighten the adjuster slightly.)

Did you account for the nut tightening the adjuster a smidge?
Zach

The base circle on the cam was made/cut improperly, off center.
Nothing wrong with the engine, 31K 120 comp on all, leak downs of 5% cold (and sitting for 2 months).

The point of this post was to make members aware of a possible problem.
I didn't say "All will do this".

If you use steel pushrods you should check base circle run out before you do!

My adjusting method account for everything including lock nut torque.
Most lock nuts pull .0007-.001 out (or sometimes add! L-series Nissan) to the adjustment.

I have also gone through the BS of setting up a dial indicator to verify how accurate my feeler gauge method is. I did not do this on my T4 as it is in-chassis.

Most folks adjust too loose...

When I'm good -.001 gauge is floppy, +.001 will not fit at all, and correct is tight with a certain amount of drag. This drag will be the same on all of the valves before I'm happy.

Many engines list a range. I choose a single number inside the rang and hit that.

I have adjusted hundreds of sets of valves over the last 40 years...

And it's a little funny. Most of the time, when I can see the cam, I set the LCA directly away from the rocker or bucket.

So, for ALMOST everything I'm going Krusty automatically!
I almost never do TDC for each cylinder. Seldom is TDC marked on the crank pully for more than two cylinders.

Especially on shim over bucket this is the BEST way as it's easier to remove the shim with the cam lobe pointed directly away...

Final point, when the valves are adjusted this way, I will commonly end up with compression test that absolutely match.
First time I did one that went perfect I didn't believe it.

The single biggest reason for compression test variation is intake valve closure point.

Each .001 of adjustment variation produces 3 degrees of camshaft duration change.
I have used this trick to see if 10-15 degrees more duration would help an engine.

[Jack Standz]

After reading about this issue you discovered I thought about a couple things.

First, I was happy that we put aftermarket aluminum pushrods in the 2056 motor. So, not only do they save valvetrain weight, they potentially avoid tight valve lash and a possible early burnt valve. Didnt have a clue that this could be an issue.

https://vwparts.aircooled.net/ACN-Heavy-Dut...p/acnhdalpr.htm

Second, we still have a 2.0 liter motor that was in a 914 we bought 15+ (?) years ago that was purchased with a burt valve. Removed the motor and it sits in the garage on a harbor freight wooden moving dolly. Still haven't torn it down yet, but someday when I'm curious, it'd be good to figure out what caused the burnt valve. Parts have been scavenged over the years, like tins, possibly the flywheel, coil, and etc. Someone put some time into building the motor as it does have ported real 2 liter heads.

The motor looks to be fairly low miles, so I suppose I thought the DAPO had run it with tight valve lash or bad machine work, or crappy parts. Hmmmmm what was the real cause?

[technicalninja]

Thanks Jack!

Even in threads I start as a PSA I learn new shit!

I wasn't aware of hot rod aluminum pushrods before your post.

Truth be told I didn't hunt...

Now I KNOW what I will use should the need arise!

Half the weight as well!

Ninja approved. (IMG:style_emoticons/default/ninja.gif)

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