Broken/stripped cam gear

RZAR · Post by **RZAR** » Tue Mar 31, 2009 9:00 pm

How common is it for the cam gear to fail on a type 4 engine? What are the causes for a cam gear to fail?

Post by **Amskeptic** » Tue Mar 31, 2009 10:15 pm

RZAR wrote:How common is it for the cam gear to fail on a type 4 engine? What are the causes for a cam gear to fail?

Rivetted gear can fail if the rivets get the slightest bit loose. Quality control? They had magnesium gears and I think they switched to aluminum because magnesium was weak. Other info welcome.
Colin

RZAR · Post by **RZAR** » Wed Apr 01, 2009 5:40 am

This happened on my fairly new rebuilt engine (7000 miles 1 year and 3 months) in my 77 bus with stock FI. Driving down the freeway at 60 mph and the engine just quit. No warning or noise just died. Cranked over the engine and no rocker movement on any cylinder. I pulled the engine stripped it and took it back to the builder. He pulled the dizzy drive gear and found the cam gear stripped. He is going to take the rest of the engine apart and call me to tell me what else its going to need. Since it is only 3 months out of warranty sounds like he is going to charge me for the work at a discounted rate. I was a little disappointed because the builder is very highly regarded by everyone and to top it all off he is only 8 miles from my house. So it seemed like a no brainier to go to him. I know not everyone is perfect and Sh*t happens even to the best of them. I'll have to see how he handles this problem. This engine ran awesome all the way up until the cam gear fail.

Post by **Amskeptic** » Wed Apr 01, 2009 7:27 am

RZAR wrote:This engine ran awesome all the way up until the cam gear fail.

It is extremely unusual to have no warning. Normally, you have a terrible mushy clatter at idle as the gear loosens up. Also, find out if the gear was an original rivetted gear-to-camshaft, or a bolt-on replacement. If it was a bolt-on replacement, the onus is on him, no ifs ands or buts. Ask to see the damage before any decisions are agreed to. Bolting gears to camshafts must be performed dead-on accurate with toothed lock washers and LocTite on the bolt threads. Check the oil pump for signs of bolt head contact. If the gear failed so fully that the crank was turning and the camshaft wasn't, expect valve-to-piston contact damage.
We are sure this was a camshaft gear failure? A distributor drive gear, the brass one, could fail silently and stop the engine cold when the distributor stops turning. . . .
Colin

Bookwus · Post by **Bookwus** » Wed Apr 01, 2009 9:11 am

Hiya Colin,

Amskeptic wrote:...... A distributor drive gear, the brass one, could fail silently and stop the engine cold when the distributor stops turning. . . .

That was my thought also, but RZAR mentioned that he was getting no movement in the rocker assemblies when the engine was turned over.

I was wondering...............would it be possible that the cam drive gear on the crank has fractured or otherwise lost its "grip" on the crank? That would kill the valve train action.

vwlover77 · Post by **vwlover77** » Wed Apr 01, 2009 9:51 am

I remember that one of our forum members, Sean G, had visited a VW repair shop a while ago and found the owner was working on an AVP engine with a few thousand miles that had quit running. Same issue - cam gear stripped out. If I remember the photos correctly, the gear did not come loose. It looked like the camshaft had been held still while the crank gear ate away the teeth in that one location. The rest of the gear appeared to be OK. It was really weird.

Sean, if you're out there, do you still have those photos?

spiffy · Post by **spiffy** » Wed Apr 01, 2009 2:07 pm

would bad gear lash do this much damage?

RZAR · Post by **RZAR** » Wed Apr 01, 2009 3:58 pm

When I was there yesterday to give him back the engine he pulled the Distributor drive out and we looked down into the hole and saw the cam gear and its teeth sheered off. I think the cam gear was a golden brown color so maybe it was the magnesium? He then told me this was a reoccurring problem and it was because of the motor oils of today (which I knew was B.S.) I told him I was using Brad Penn so that ruled that out. Then he said that to fix the problem he wanted to use a steel straight cut cam gear because it was stronger. I was kind of blown away at this. My bus is not a race car. Everyone says this guy is the greatest. Everywhere I go, The Samba, STF, and here. I am starting to lose my faith in this guy real quick. I'm very interested to see how he is going to treat my problem. Yes it is out of warranty (by only 3 months) but it only has 7000 miles on it.

Hippie · Post by **Hippie** » Wed Apr 01, 2009 4:13 pm

spiffy wrote:would bad gear lash do this much damage?

Nope. I don't think so.
Same thing happened to a friend of mine's 2 liter '77. Only 1500 miles since a rebuild. The teeth weren't stripped but the camshaft gear wallowed out on the rivets and sheared off the rivet heads. We tore it down and put an old, moderately worn VW camshaft back it it.
Not good practice when the lifters are new and not worn to the lobes, but screw new. New parts suck.

spiffy · Post by **spiffy** » Wed Apr 01, 2009 6:52 pm

Something HAD to have been assembled wonky, that is a lot of destruction. Guess you won't know until the case is split and even then the culprit might not present itself. Scares the poop outta me.

The straight cut gear would have just knawed things up more, that in itself sounds like a duct tape fix.

Post by **Amskeptic** » Thu Apr 02, 2009 6:05 am

What magnificent travails, what odious travesties of sore misjudgment betwixt failed metallurgy and dastardly scornful misappropriation of languished fact weighes my breast in fatigued wondrous bedevilment. . . uh sorry, I saw King Lear last night.

I do not know of any assembly error that could eat a gear to death save one:
Too tight at initial assembly would prevent an oil film. Steel gear would gall soft magnesium or aluminum. Galled surfaces would never get a protective oil film. Gear would fail. That is my guess and I am sticking to it . . . howl, howl, howl thy fate is not only in the hands of knaves of devious intent.
Colinbard

vdubyah73 · Post by **vdubyah73** » Thu Apr 02, 2009 1:50 pm

Maybe the center and outer diameter were not concentric. Faulty part, used to work in a machine shop, not every piece gets inspected. First couple get inspected as they come off the machine, then the run just runs till done. When done, depending on quantity made, random pieces are inspected for tolerance. Set ups to hold parts on the table can and do drift. The shop I was in made many of there own gears. The machines they made put anything from corn flakes to Jack Daniels in their containers. Kellogs, Proctor & Gamble, Jack Daniels, even did tooth paste for someone. The kinda machines you see on those "how they do it" shows on the TV.

RZAR · Post by **RZAR** » Thu Apr 02, 2009 4:09 pm

Still waiting on a phone call from him. If this guy is as good and trustworthy as everyone says he is hopefully he will work with me on this.

RZAR · Post by **RZAR** » Sun May 31, 2009 7:14 pm

Totally overdue but here are pics of the failed cam gear. Builder claims cam was redone by Schneider cams here in San Diego. Redone but with original cam gear as you can see the rivets. Who knows how old or how many miles was on this gear. Builder claimed it was due to todays oils not containing enough zinc (but I use Brad Penn 20/50). What does zinc have to do with gears? If that was the case why aren't oil pumps failing? Anyway he replaced the cam gear with a straight cut Magnum gear set. Seems like overkill.

Hippie · Post by **Hippie** » Mon Jun 01, 2009 2:53 pm

I know a little about zinc in oil (zinc dialkyldithoiphosphate) and I'm very very skeptical that todays reduced levels would have anything to do with a cam gear failure. Although I do recommend a zddp containing break-in additive for safety of flat lifters for the first 1000 miles or so with a new engine.
ZDDP is a consumable, heat activated anti-wear additive that prevents galling when there is extreme pressure. It prevents true metal to metal contact and is gradually consumed in the process. It (the phosphorus component) is hard on catalytic convertors in the long run, so they have reduced the amount from about .11% to 0.8%. Modern non-racing engines use roller lifters and usually overhead cams, and are safe with much less zinc.
Most oils have enhanced their additive package and base oil characteristics to make up for this. The latest oils actually have raised the bar on wear reduction the make the ILSAC GF-4 specification, lower zinc notwithstanding.

Itinerant Air-Cooled

Itinerant Air-Cooled

Broken/stripped cam gear

Broken/stripped cam gear

Re: Broken/stripped cam gear