Stock Engine eating cam gears

[Dwayne1m]

Stock engine, case #AK069898

This engine came out of my 74SB that I restored. Rebuilt it once and it wiped out the cam gear in about 200 miles. I figured I did something wrong but nothing jumped out. Had a guy who has been building them for 40+ years do all the measuring and even put the crank & cam in to test for the 2nd rebuild and it appears to have wiped out the cam gear a 2nd time in less then 300 miles. It spun easily by hand before I put the cylinders & pistons in. Could spin it with a ratchet then too with not much effort. Ran fine. He has no idea why this is eating cam gears. Only thing I can think of is the case is shot. All measurements were within spec. All torque was done to spec. It's still a stock as stock can be 1600. During the 1st rebuild I might not have tightened the 2 smaller nuts at the flywheel side of the case before I torqued the 6 main nuts, but nobody here seemed to think that was much of an issue. The 2nd rebuild I did torque the 2 outer nuts before torqueing the 6 main nuts. The bearings after the 1st rebuild looked ok except for where you could see bits of the aluminum from the cam gear scratch them. I'm frustrated and at a loss. Unless someone can tell me why it's eating the cam gears I'm leaning toward the case doing something funky, like flexing or warped. Now the decision is 1-new case and transfer the parts, 2-buy a short block from a "reputable builder" hoping I get a good one, 3-buy a whole new engine, and 4-Try and find a "good" used case and roll the dice. I see a new case goes for $800, but I can buy a complete engine for just a little more. OK, time for advice from the engine gods.

[bluebus86]

cam gears.... hum I suppose misalignment could be an issue, but that would be really weird, Gear not seated correctly on crank?, not correct on cam shaft? align bore done really bad? Cheapo bad gear(s) ? Binding of cam shaft do to interference, or too tight bearings, or loss of oil to cam bearing(s)?

Photos?


Good Luck

Bug On!
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[Dwayne1m]

Still stock bearing sizes.

Didn't tear it apart yet but the oil is silver just like after the 1st cam gear was eaten.

Everything lined up. He even "blued" the cam gear to see how the contact pattern was and it was fine.

I think if it was misalignment it wouldn't have spun as easily as it did.

The 1st cam gear was "sharpened" down to a razors edge at spots. I can only imagine the same is happening to this gear. He installed a new gear on the crank for the 2nd rebuild.

[74 Thing]

Maybe the camshaft and crankshaft are not aligned (parallel), or a bad quality cam gear or mismatch with the crank gear.

[TDCTDI]

Something is binding the cam? Maybe warped block, wrong size bearings, valve springs too tight.

Perhaps the old drive gear on the crankshaft was damaged by the previous issue & is causing the tips of the teeth to scrape over the flats of the cam gear. Incorrectly align boring causing the cam & crank to mesh too tightly?
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[VW_Jimbo]

Maybe call the camshaft gear manufacturer and ask if they had a improperly hardened run of gears. Maybe they missed it on the right Rockwell number!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Lingwendil]

New or aftermarket gears? Good Used VW gears? Are they 0, +1, +2, -1, -2? If you use the wrong ones they will mesh too tightly and chew eachother up...
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[VW_Jimbo]

[vwoldbug]

Have all cam gears had the same gear on the crankshaft . I would change the gear on the crank shaft .

[Lingwendil]

I've seen two engines with very thrashed gears before, and I've seen the rivets loose from too-tight gear mesh.

I think most aftermarket gears are at 0? I've seen an older EMPI one that was pretty tight though, and needed a looser crank timing gear to fit correctly.

A bunch of builders save good used gears from stock teardowns to reuse on new builds, dig through the pile and find one with a perfect fit!
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73 super beetle thread http://www.thesamba.com/vw/forum/viewtopic.php?t=649622 Back on the Road!

Modify your Kadrons for SVDA http://www.thesamba.com/vw/forum/viewtopic.php?p=8115884#8115884

Cast iron VJU4BR8 SVDA reference thread- https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

Need replacement filters for original Kadron aircleaners? WIX #42087 is a perfect fit, as is Napa Gold #2087!

[Dwayne1m]

Just a refresher so nobody has to read all the threads.

1st rebuild:
original crank and gear
original cam and gear(0)
stock size bearings
heads were redone. Can't answer if he put new springs in or not. I'm assuming he did.
compression was 150 all around
new oil pump & oil light worked as it should
new pistons & cylinders
end play .004
Lasted 200 miles

2nd rebuild:
original crank but new gear
He gave me a used cam(-1)in great shape with its original gear
stock size bearings
same pistons, rods & cylinders as rebuild #1 all in original positions.
turned free, no binding at all, ran very good.
Still 150 compression
end play .005
Lasted 300 miles

Bone stock and not driven like a wild man. I'm old. Racing days are over.

[VW_Jimbo]

Maybe go to a -2?

I was taught to test, two separate ways, for the play at the gears, during a build. Both use only feel, so it is hard to reference across the internet. But...…..

I would place the crank and the cam in the case half, in their bearings. Then, I was taught to rock the cam back and forth. You should hear the lash but not be able to see any movement.

The next test follows the first one and is a double check of the first findings. After you feel comfortable with the free play between the gears, you turn the crank CCW and watch the cam. If everything stays in place, all is good. If the camshaft starts lifting out of the case half, the cam is too tight. Turns that cam bought directions, because sometimes shit changes!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Dwayne1m]

I'm new to rebuilding these engines but I thought the stock cam gears were all the same and the number was just the way the gear was positioned on the cam. I thought the number on the gear just tells you valve timing in relationship to the crank. Am I wrong? If all cam gears are different I would think you would have to mate the correct crank gear to the correct cam gear. Are all stock crank gears the same?

[Lingwendil]

The timing gears on the crank should all be more or less the same, but the cam gears were marked in several under and oversizes in order to give proper mesh on differently built engines, in order to make up for tolerances stacking up between the main bearing bores and the cam tunnel bores during machining.

Some crank timing gears will appear fine but be undersized on the outside due to wear or manufacturing differences.
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73 super beetle thread http://www.thesamba.com/vw/forum/viewtopic.php?t=649622 Back on the Road!

Modify your Kadrons for SVDA http://www.thesamba.com/vw/forum/viewtopic.php?p=8115884#8115884

Cast iron VJU4BR8 SVDA reference thread- https://www.thesamba.com/vw/forum/viewtopic.php?t=...mp;start=0

Need replacement filters for original Kadron aircleaners? WIX #42087 is a perfect fit, as is Napa Gold #2087!

[ashman40]

Did you mechanic check the cam/crank backlash and whether an over/undersized cam gear was needed?

I don't have my Bentley handy to find the spec for the backlash. I found this thread which discusses the backlash and describes the DIY method detailed in the Tom Wilson book.
https://www.thesamba.com/vw//forum/viewtopic.php?t=532425
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[Dwayne1m]

I can't answer if he used a dial indicator to measure it or not. What I can say is that it turned free by hand , and with the case in half the cam would not back out of the bearings either way I turned the crank.

[VW_Jimbo]

What does the inside up by the gears look like? Any pictures of both halves of the case?
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[volksnhousin]

To me the sharp “shark teeth” worn teeth mean the gear mesh is on the loose side... Teeth only contacting a small amount on the outermost portion of the teeth. Perhaps experimenting with a + gear instead of a - gear is the way to go. The cam gear backlash test that was mentioned should be be done if you can do that.

[Dwayne1m]

These are pics of the original cam & gear. I must make 1 correction though. For some reason I had it in my head this gear was a (0). It's actually a (+1). My mistake. Either way, it's the original cam and gear mated with the original crank and gear and it lasted 200 miles. It's not worn all the way around as you can see. If it means anything the worst of the wear is directly opposite the "dot" for aligning with the crank. As for pics of the case, I don't have any and I didn't drop the engine to inspect it yet, but all things for me point to the cam gear being damaged again.

[Bashr52]

The way that is worn leads me to believe the cam is running in an elliptical pattern instead of a smooth circle like intended. It gets tighter/looser on the crank gear depending on where it is in its rotation. Is it just one section that is worn that bad, or are there two areas opposite to each other?

The other thought is the cam gear was shifted on the cam and the center-lines were not in the same plane. Since you have tried two different cams with he same results however, leads me to believe it's a case issue.