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Sun Mar 09, 2025 9:21 am

I am having trouble with an adjustable CB helical aluminum cam gear. I am using a used German crank gear that has the VW emblem on it, but it has some miles on it (shiny on the gear teeth). Using a 74mm CB crankshaft, a web cam, and the used and shiny tooth VW crank gear,.

So I set the end play on the cam bearings, but when I check the gear backlash there is as much as .005" on one side (nearest the woodruff key) then there is little to no backlash on the opposite side of the woodruff key. The book indicates that backlash specs are up to .002" so I am already over double that measurement in one spot.

What should I check at this point? I am thinking of getting my gear puller and pull off the crank gear and maybe even replace with a new Brazilian made crank gear. I wlll pay close attention to the woodruff key since if it is too tight or tall or wide it may be causing something to bulge. It was tight to fit and I had to lightly sand it and deburr the slot in the crankshaft (maybe I should have measured the crank at that spot to see if when installing the changed the diameter).

What should I be shooing for as far as backlash is concerned? I know vw made gears form -7 to +7, but I can't throw money at random gears hoping something may fall in order.

So I am going to pull the gear stack and check the woodruff key. I can order a new crank gear and install that. I am not sure where to go for a new cam gear. Should I be checking runout somewhere? Maybe I can change the mounting holes on the cam gear and run it and depending on where it is loose again may help me determine if it is a crank gear or cam gear causing the problem.

Sun Mar 09, 2025 10:20 am

My guess would be you have a buggered tooth or 2 on the cam gear.
Maybe cycle it back and forth through the tight spot by hand then get a magnifying glass and look for a shiny spot.
It doesn't take much to bang up a stock magnesium gears.
I've seen it and with a small file it can be cleaned up pretty easy.

Sun Mar 09, 2025 10:29 am

It is an aftermarket aluminum CB gear.

I am concerned since there is no play on one side and then 180 degrees away it has .005" backlash at the cam gear tooth where the book specs are up to .002"

If there was a consistent backlash all around then I could be comfortable searching for a different gear with a different pitch on the gear teeth.

Right now I am kind of stumped, although it may be the aftermarket gear.

Sun Mar 09, 2025 10:39 am

I would trust the german crank gear to be more likely ok, than the aftermarket cam gear. If the crank key was too large, it would cause interference on the key side, not opposite.

Maybe measure crank and cam for detectable run out. Either could be bent slightly

Mon Mar 10, 2025 9:14 am

It could be a couple of things, or a stack up of tiny variances.

The big flange diameter on the cam could be non-concentric by a bit. Or the counter bore machined into the gear could be machined non-concentric. It would only take .002" each being off, and and it would make a big difference in backlash.

Brian

Mon Mar 10, 2025 9:39 am

I will put a dial indicator on the cam mounting flange today to see where it is.

How do you suggest I check the cam gear?

I will probably change the way the cam gear is mounted on the cam by moving it over one hole and see where the loose and tight spots now occur so I can determine if it is cam gear related or crank gear related.

If somehow I could get this gear shifted over so it was .002 throughout I would be fine with that.

Mon Mar 10, 2025 10:21 am

Havent tried this, but maybe opening up the id of the cam gear with a drum roll sander on a dremel. Couple thou might be enough to get it centered better

Mon Mar 10, 2025 3:37 pm

I verified by installing the cam gear onto the crank gear in different positions that the loose part always was happening at the same position on the cam gear regardless where it was contacting the crank gear.

I also measured the Web cam mounting for run out and it was near perfect.

Finally I took the cam gear off and measured it and sure enough I verified it was non-concentric.

I purchased this item a while ago, but I will shoot Marianne at CB an email to see if she will assist.

Thanks for the help. I guess this build is on the back burner.

Wed Dec 03, 2025 5:09 pm

Hey 74 Thing,

Whatever became of this?

I just got my 1399s mounted up and am having a very similar problem. .001" backlash when timing marks aligned. Up to .005" when cam is rotated 270* counterclockwise. .001" at 90* counterclockwise on the cam gear. Zero backlash when the cam gear is 180* away from timing marks aligned (360* crank), and at 360* crank rotation, it shouldn't be the crank gear - I'd suspect the crank gear if backlash went to zero at 180* crank/90 or 270* cam.

Cam gear measurements turned out to be .005" axial runout on the cam gear, which would probably cause the backlash to go egg-shaped if the gear teeth are following the face of the gear. .002" axial runout on the cam flange, which will increase over the distance to the edge of the cam gear, further away from the center. This feels like either the cam flange is off or the cam gear teeth are not concentric to the cam flange relief in the gear. Or both.

Need to call CB tomorrow.

In the meantime, did you get yours resolved?

And for the world to weigh in, is my logic off?

Wed Dec 03, 2025 6:36 pm

Lay an old stock cam and gear in the case half and see what you get, preferably one with a dished, riveted gear on the cam. That will narrow it down to a bad cam/gear or something wrong on the crank end.

Wed Dec 03, 2025 7:17 pm

Bugsy61 wrote: Lay an old stock cam and gear in the case half and see what you get, preferably one with a dished, riveted gear on the cam. That will narrow it down to a bad cam/gear or something wrong on the crank end.

Appreciate the response. For clarity, the crank is currently removed from the case. After seeing two different backlash readings at the same point on the crank, I'm kinda putting that one at the bottom of the probability list for now. So the axial measurements were taken with nothing but the cam in the case, first with the gear on (.005") and then w/o gear (.002").

Just checked radial runout at the cam gear flange w/o gear - less than .001".

This cam flange axial runout issue has me a bit concerned though - it will amplify with the gear in place as we get further from the centerline of the cam. And if the gear is riding like a swash plate, I'd expect the lash to change as it rolls around.

I'll call CB in the morning to get their take. Will start putting backup plans in place too, in case this turns out to be the root cause.

Wed Dec 03, 2025 8:30 pm

I spoke with Marianne at CB and mailed it back in at my expense and they gave me a credit once they checked it out. It was machined off center. I used another cam gear and it worked out fine. If that did not work out then I was going with straight cuts from CB.

Info here
https://vwparts.aircooled.net/Woodruff-Key-Crankshaft-Timing-Gear-8x13x32mm-p/111-105-213.htm

Wed Dec 03, 2025 9:38 pm

Oh, I just realized you were using the aluminum adjustable gear. And it was off center?

That’s the same gear I used, the one that shredded itself in my 2027. Which is why I’m now putting my 1600 back together as a stop-gap. This time with steel straight cuts. And still having problems.

Interesting.

I wonder if they had a bad run of the aluminum adjustable. Seems worth looking into…

Wed Dec 03, 2025 11:47 pm

Yes, I measured it slightly off center. I was using the helical alum adjustable gear. I was also using an OEM crank gear. It took me a while to figure out that it was the cam gear causing the binding in one spot.

I see you are using the straight cuts-could be the same problem. I determined it was the cam gear since no matter how I oriented the cam gear to hit a different part of the crank gear it would always bind on the same area of the cam gear. I measured the run out on my cam as well. Finally measured the teeth to centerpoint and it was very slightly off-enough to cause tightness at one point then was too much play on the opposite side. Measure closely-hopefully you will figure it out or just swap gears and try again.

Thu Dec 04, 2025 9:08 am

I had a similar experience with the 1399 . Backlash was .002 at the point where keyway was facing cam gear. And .0035 at 180 degrees around from keyway. Running a webcam and stock vw crank gear. Close enough to run.

Link. https://www.thesamba.com/vw/forum/viewtopic.php?t=802532&start=20

Thu Dec 04, 2025 9:38 am

early wrote: I had a similar experience with the 1399 . Backlash was .002 at the point where keyway was facing cam gear. And .0035 at 180 degrees around from keyway. Running a webcam and stock vw crank gear. Close enough to run.

Link. https://www.thesamba.com/vw/forum/viewtopic.php?t=802532&start=20

That sounds like the crank gear was being pushed a little out of round. I'm getting variances in gear lash with the crank at the same place, and then even bigger variance when the woodruff key is out of place to effect anything.

If I had .002 and .0035, I'd probably run it too. But no f'n way with 0 backlash. I already have one engine that destroyed its aluminum cam gear sitting in the car waiting to be torn down after this one is up and running again. I'm not losing another engine...we're going to get to the bottom of this before it goes together and in the car.

I gave CB the details on my findings and purchase documentation this morning. They're working on it. I'm waiting on them to get back to me so we can figure out how to proceed.

Sorry 74, wasn't trying to derail this. It was initially about the aluminum adjustable (1419?). I didn't pick up on that until after I posted but you opened up a really important discussion. Thanks for your feedback and understanding.

Thu Dec 04, 2025 10:31 am

Sometimes the woodruff key for the crank can be too big and push the crank gear slightly causing problems

Thu Dec 04, 2025 12:05 pm

Rob, agree with you completely. I wouldn't like the variance that you describe.

I too had a cam gear backlash problem and thus replaced keyway, cam, gears and cam bearings, on a build that was only a year old.

My original problem came from a keyway and crank gear that wasn't tight enough or so I have surmised.

Ok so far but it only has less than 100 miles on it due to this winter weather we are having around here.

Cheers and good luck. Early