Funky Frustrating Starter Shimming

RVbigBlock · July 17, 2011

My first post on this forum, trying to get some ideas on what could be wrong. We have a 1983 Alegro RV. Its powered by a GM 454, old carborated engine. It runs well and strong, but we're confused with the starter. We recently installed a reconditioned starter(like new). It was having some trouble starting, but once running is great. When we installed the new starter, it sounded horrible. We shimmed it until it sounded and started perfect. After driving around for about 20 minutes, we parked and decided to restart. It then sounds like we didn't shim it at all. So we tried reshimming(figuring the current shims are no good when the thing is hot). It starts, but sounded pretty rough. So we reshim, and it sounds perfect again. Drive around a bit and its right back where we started.

We're pretty sure its not the flywheel, because when shimmed right, until it starts it sounds perfect. As I understand it, it wouldn't shim right at all if the flywheel were messed up. Can something else move? Every mechanic I ask about it is mystified. Any ideas?

Doug_Scott · July 17, 2011

My first post on this forum, trying to get some ideas on what could be wrong. We have a 1983 Alegro RV. Its powered by a GM 454, old carborated engine. It runs well and strong, but we're confused with the starter. We recently installed a reconditioned starter(like new). It was having some trouble starting, but once running is great. When we installed the new starter, it sounded horrible. We shimmed it until it sounded and started perfect. After driving around for about 20 minutes, we parked and decided to restart. It then sounds like we didn't shim it at all. So we tried reshimming(figuring the current shims are no good when the thing is hot). It starts, but sounded pretty rough. So we reshim, and it sounds perfect again. Drive around a bit and its right back where we started.

We're pretty sure its not the flywheel, because when shimmed right, until it starts it sounds perfect. As I understand it, it wouldn't shim right at all if the flywheel were messed up. Can something else move? Every mechanic I ask about it is mystified. Any ideas?

When you say it does not sound right, what does that mean? Have had the starter checked draw when hot? Have you checked for missing teeth on the ring gear?

Shimming is almost aways correct if set properly cold. Are you using start shims? Stater shim is long enough to engage both bolts. You may want to try disconnecting the distributor power wire from the cap (the thin green wire is for the tach, so remove the other one. Do this when the truck is acting up.

If the starter sounds ok with the ignition disabled, then you have either too much timing, or carbon build up in the cylinder (causing pre-ignition when carbon glows and sparks off the fuel).

RVbigBlock · July 17, 2011

When I say doesn't sound right, I mean its grinding, as if the mesh is very wrong or not engaging just grinding metal off. Sometimes it won't even turn over, it just grinds and sounds terrible. How do we check the "Starter Draw"? I would think that if the engine were locking up somehow, that the starter would engage and just not turn over, almost like a dead battery. This sounds like the mesh is wrong, and its grinding. We are using a starter shim kit from autozone. They are .020, .040, and .060 in thickness. We got it to sound perfect with just the .040, but after it starts once, it grinds again. Even after letting it cool, with the same shim that got it to start perfectly, it grinds again. Whats weird, is you can try starting the thing as long as it takes once you get the shim right... that time. After starting it, driving it, or whatever, it stops working. That's why we're so confused. Thank you for trying to help.

Doug_Scott · July 17, 2011

You need to take the shield off of the bottom of the transmission and take a look at the teeth on the ring gear. I think you will find it is missing a few teeth. You can also look that meshing of the bendix gear and the ring gear at that time as well.

When you shim the starter you are actually moving the starter further away from the ring gear. Normally the shims are required to eliminate the two gears from binding. You can try only shimming bolt and see it will move the starter closer, but I don't think it will. This really sounds like the ring gear is missing teeth.

RVbigBlock · July 17, 2011

We removed the cover the first time we tried, and while we can see some wear, the teeth appear to all be there. Wouldn't the starter spin free if teeth were missing when it hit the damaged area? Like I said, the starter works perfectly, and then it as if the shim is completely wrong. That's why we're confused, it works perfectly then acts like we did nothing at all. Is the bendix gear the one on the starter? If so, other than a few nicks, and scratches, its all there too.

Doug_Scott · July 17, 2011

We removed the cover the first time we tried, and while we can see some wear, the teeth appear to all be there. Wouldn't the starter spin free if teeth were missing when it hit the damaged area? Like I said, the starter works perfectly, and then it as if the shim is completely wrong. That's why we're confused, it works perfectly then acts like we did nothing at all. Is the bendix gear the one on the starter? If so, other than a few nicks, and scratches, its all there too.

Yes, the bendix gear is the one in the starter that engages the flywheel. Just my age showing. The teeth do not have to be competely gone to have it grind, if the tooth is ground half way across its face, you may get grinding sound, but the tooth will still mostly be there. Technically, the only way a tooth could be completely missing is if it was broken off flush, normally this does not happen, only part of the tooth gets broken, and if is only partially broken, grinding can happen.

Look at all the teeth, they are only about 3/8 to 1/2 inch in size, does not take much to be gone before it grinds.

In your initial post, you said "It was having some trouble starting". Was it grinding then? If not, then you may have a rebuilt starter with the wrong bendix in it (bendix is the assy that gets pushed out by the solenoid), or the entire starter may be wrong for your application. Take a look at the bendix gear as it meshes with the ring gear. Is it engaging at least the complete tooth on ring gear? You should be able to pull the bendix out manually to see this.

WARNING: Make sure you disconnect the battery before doing this, prying the bendix out will make the starter spin if battery is connected!

You may want to search for what the desired clearance is between the shaft and the ring gear and make sure that is correct. Also make sure that shaft does not move due to warn end cap bushing.

If this was grinding before you changed the starter, spin the engine by hand (socket and ratchet on the harmonic balancer centre bolt) and check the ring gear for runout, both fore to aft, and side to side. I have seen a ring gear break (in the middle where the bolts are attaching it to crank) and it would basically spin a bit before jamming up on itself. When it jammed up, it would be off to one side slightly, or even pushed back a bit, but still forced back together. Hard to explain that part. It also could have been hit by something on the road, and bent rearwards at some point. This ring gear is not a flywheel, it is a piece of metal that is like an eight of an inch thick with the actual ring gear welded on to it. With the shield off, you may be able to see the complete lower part of the ring gear, look for a crack or break in it.

RVbigBlock · July 17, 2011

Ah, so the gear, not the flywheel could be damaged and this is why they don't match up all the time? A friend mentioned and out of round flywheel, and we really hope that isn't the case. I'll pull the starter and inspect the gears. I took the original to a specialized starter/alternator repair place. The starter came back looking brand new. I assume we have the correct starter, but we are human. Our next step is to simply take it to a mechanic the next time we manage to start it. Once running it runs pretty well. We just have to be able to start it more than once. Thanks for all the help!

Doug_Scott · July 18, 2011

Ah, so the gear, not the flywheel could be damaged and this is why they don't match up all the time? A friend mentioned and out of round flywheel, and we really hope that isn't the case. I'll pull the starter and inspect the gears. I took the original to a specialized starter/alternator repair place. The starter came back looking brand new. I assume we have the correct starter, but we are human. Our next step is to simply take it to a mechanic the next time we manage to start it. Once running it runs pretty well. We just have to be able to start it more than once. Thanks for all the help!

I am not sure I have explained correctly. I doubt the gear on the starter is damaged, but, stranger things have happened. If you try to spin the gear by hand, you will find it spins one way easy, and not likely to spin the other way. If you can make is spin easily in either direction, that is your problem.

When I say ring gear, I am referring to what you call flywheel. The flex plate is the part that the ring gear is welded to. A flywheel is what the clutch mounts to when you have a manual trans. It is big and heavy.

RVbigBlock · July 18, 2011

Ah, so the gear, not the flywheel could be damaged and this is why they don't match up all the time? A friend mentioned and out of round flywheel, and we really hope that isn't the case. I'll pull the starter and inspect the gears. I took the original to a specialized starter/alternator repair place. The starter came back looking brand new. I assume we have the correct starter, but we are human. Our next step is to simply take it to a mechanic the next time we manage to start it. Once running it runs pretty well. We just have to be able to start it more than once. Thanks for all the help!

I am not sure I have explained correctly. I doubt the gear on the starter is damaged, but, stranger things have happened. If you try to spin the gear by hand, you will find it spins one way easy, and not likely to spin the other way. If you can make is spin easily in either direction, that is your problem.

When I say ring gear, I am referring to what you call flywheel. The flex plate is the part that the ring gear is welded to. A flywheel is what the clutch mounts to when you have a manual trans. It is big and heavy.

Oh ok, I'm more familiar with old air cooled VWs... This is the first GM I've really worked on. I plan to pull the starter again and take a close look. I'll try rolling it both ways. If I can't get this right I'll take it to a shop. It just seems like it must be something simple I'm missing. I'd rather save some $$, and learn a thing or two about this old rig. I really appreciate the help!

RVbigBlock · July 19, 2011

Today I called the shop to check on the RV. So far, they found a broken part in the starter(I forget what, we couldn't tell), and one of the bolts to hold it in place was the wrong size. It sounds like the wrong bolt(metric, was in there before, have no idea for how long or why it was there) allowed the starter to move. This is why it would start once, then not again till it was reshimmed. So apparently, the starter is working correctly now.

I'm getting them to fix the alternator as well. I really appreciate all the help. I had no idea the bolt being a "Wrong" size would allow the starter to shift. It seemed to be locked down pretty well... DOH!