TheSamba.com :: View topic - '71 bus motor assembly

Tue Feb 08, 2011 3:18 pm

First engine rebuild...assembled and installed crank...turns just fine....filed notch in case for tab on dual thrust cam bearing (after consulting local VW shop)... installed new cam... binds after about a quarter turn of the crank going one way one way lifts cam out of bearings going the other. I also noticed small metal shavings from cam gear where the tip nearest the flywheel on the crankshaft gear contact.

I tried putting the old camshaft in...same problem. I tried switching crank and cam to other case half (in case I hadn't filed a deep enough notch for thrust bearing tab)...same problem.

I've read other threads on similar topics but they seemed to be about binding that occurred when torquing the case or with a new cam.

Why would the original cam bind without any tightening?

I'd greatly appreciate any help.

Tue Feb 08, 2011 3:21 pm

My first thought is that you have a bent cam because this happened to a friend of mine. If both cams are binding then you must have something in there wrong.

Tue Feb 08, 2011 3:26 pm

what is causing the cam to pop out is also what is making the shavings. the side of the gear is slightly dented by using a pipe to slam the gear onto the crank. doesnt mean necessarily you did that, but someone dented the gear. when you dent the gear on the side, the metal has to go somewhere, so it bulges up on the gear tooth cheek. this causes interference for the cam gear. you need to file it down.

to install the gear, heat the gear to 180F in a pan full of oil, apply oil to the crank snout, and after lining up the gear groove carefully with the crank woodruff key let the gear drop down the snout to the #3 bearing shoulder. but you dont need me to tell you this if you have and read the Bentley service manual.

Tue Feb 08, 2011 4:34 pm

dansvans wrote: what is causing the cam to pop out is also what is making the shavings. the side of the gear is slightly dented by using a pipe to slam the gear onto the crank. doesnt mean necessarily you did that, but someone dented the gear. when you dent the gear on the side, the metal has to go somewhere, so it bulges up on the gear tooth cheek. this causes interference for the cam gear. you need to file it down.

to install the gear, heat the gear to 180F in a pan full of oil, apply oil to the crank snout, and after lining up the gear groove carefully with the crank woodruff key let the gear drop down the snout to the #3 bearing shoulder. but you dont need me to tell you this if you have and read the Bentley service manual.

The interference seems to be on the side of the gear towards the rods/flywheel not the side somebody (other than me) might be inclined to hit with a pipe. Could something similar have occurred when the local VW shop pulled the gears off my old crank?

When I installed the gear I heated it with a map gas torch and it slid on smoothly (i think I gave it a couple light taps with channel locks I placed it on with but just to wiggle it on, not to force it down.) I've mostly been following the Bug Me video.

Tue Feb 08, 2011 5:28 pm

good to know you are following the directions.

yes, gears get damaged when being removed. not as common, but it happens- sometimes a gear will jam as it is being slid on, and someone will use a gear puller without a splitter to get it off. the jaws dig in and mash the teeth. or, more likely, gear teeth get mashed when dropped or dropped onto.

regardless of theory, the key here is that you saw shavings. trace it to the source by rolling it backwards slowly while someone holds the cam in the saddle. you will feel the resistance if you have your senses turned up. then inspect in that area to find the mashed tooth. sometimes it is easier to see the cam gear damage (caused by the crank gear) first, and then find where that damaged area meets the crank gear. because of the damage being on the bearing side, you will have to remove the crank gear to file back the gear cheek bulge.

this is a very common thing. 19 times out of 20, if the crank throws the cam out of the saddle, it is because of a gear being mashed. happens to cam gears too, but in this case, if both cams do it in the same place, then the crank gear is the cause.

Tue Feb 08, 2011 6:40 pm

This sounds right, I will try what you've said. I was already planning to remove the gears to make sure there weren't any shavings in the adjacent bearing.

Is it possible to remove them without the VW specific gear puller? The vw shop is an hour away.

Also, thank you guys for the rapid and useful responses. My only other experience with a forum like this was when I was trying to diagnose an intermittent electrical problem on my '08 Mazda truck. Apparently, the late model mazda tinkering community is not as well established (I suppose that won't surprise too many people here.)

Tue Feb 08, 2011 9:06 pm

just make sure you locate all the mashed metal and mark the location before you remove the gear. clean the teeth with solvent and mark location with a marker. easy to lose track of the dent once it's off! :shock:

you can use a generic gear puller only in combination with a "bearing splitter." presses also require a splitter.

the VW suppliers all seem to have some sort of specialized VW puller with a yoke (collar) that is specially designed to be thin enough to fit between the bearing and gear, while also being the right diameter for the VW crank journal.

Tue Feb 08, 2011 9:34 pm

I agree with Dan on the cause. One thing I would like to confirm is that you have not swapped the gear on the camshaft for another one? Each gear has a number on it. You need to match those numbers if you swap gears. +3, +2, +1, 0, -1, -2, -3 etc. Sometimes the replacement gears, especially if bolted on aftermarket are not concentric with the cam. We ran into this on a replacement brazilian gear.

Wed Feb 09, 2011 10:02 am

yeah, extreme gear mismatch to the case would be the other 1 out of 20 reason for the cam being thrown out of its bearing saddle

Wed Feb 09, 2011 10:30 am

out of curosity, did you ever test the cam by itself and the crank by itself?

If both are Ok alone, install the cam so the timing marks align (two dots and one dot). Spin gently and where it binds make a mark with a black magic marker on each gear.

Remove the cam gear and rotate it 90 degrees. Spin it again - see if it binds at the magic marker mark on the cam or on the crank gear. That will tell you which one is the problem.

Remove the cam so you don't accidently forget it and leave it not in time.

Wed Feb 09, 2011 3:56 pm

SGKent wrote: One thing I would like to confirm is that you have not swapped the gear on the camshaft for another one?

he has both a new cam and the old used cam.

both bind. So...

i am thinking crank gear, but it is possible for both cams to have dented cam gears.

where each binds is the definitive test.

Fri Feb 25, 2011 8:17 pm

I consulted the local shop and didn't like the advice I got so I ordered a crank gear puller so I could take matters into my own hands.

I ordered a new gear at the same time because shipping to Hawaii is so expensive I'd hate to regret not getting the $20 gear in the first place.

I had already done what I could to locate the damaged teeth and after pulling the gear it was easy to see the damage. Five teeth on one side and six teeth, pretty much 180 deg around on the other side, are pretty mangled. This is the side of the gear that faces the flywheel when installed.

I'm guessing some kind of careless rig job when they pressed it off for me the first time.

Fri Feb 25, 2011 10:23 pm

mmvandr wrote: I consulted the local shop and didn't like the advice I got so I ordered a crank gear puller so I could take matters into my own hands.

I ordered a new gear at the same time because shipping to Hawaii is so expensive I'd hate to regret not getting the $20 gear in the first place.

I had already done what I could to locate the damaged teeth and after pulling the gear it was easy to see the damage. Five teeth on one side and six teeth, pretty much 180 deg around on the other side, are pretty mangled. This is the side of the gear that faces the flywheel when installed.

I'm guessing some kind of careless rig job when they pressed it off for me the first time.

or hammer