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  #1  
Old 10-25-2007, 12:46 AM
cmac2012's Avatar
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Timing belt woes on BMW 325i

Woe is me. I done done the dumbest thing of my shade tree mechanic career. I replaced the timing belt on my bimmer just fine about 5 years ago. This time, I was in a hurry, late at night. Oops. Err in haste, repent at leisure.

Somehow, I put it on one tooth out of place. I think it was because I turned it counter-clockwise a bit, which loosened the tensioner a tad. I then rotated the crank 720 degrees, no noise, no unusual resistance, and discovered my error. I corrected it, put it all together, and I'm getting a nasty random clunking sound when I start it.

My local discount parts man, a wealth of info, says I bent a few valves and I'm think he's right. Says that one tooth off won't ruin the head but also says pulling the head at this age (265K) can result in some blow-by upon reassembly.

I've posted this on a couple of Beemer forums, a little bit of help but not too much. One guy said that he didn't think one tooth off would bend valves. He thinks it might be a loose belt cover or other small problem. I know I was under the thing for a long time with my stethoscope and couldn't find any obvious culprit. The noise did sound like it was coming from up front.

So anybody have a clue, specifically: would rotating it one full cam turn with one tooth off bend valves?

BTW, I'm determined that this experience is going to make a better man out of me. I have to hold onto that hope cause I feel like a bleepin' idiot if I don't.

In short . . . .DOH!!!

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1986 300SDL, 351K
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  #2  
Old 10-25-2007, 12:53 AM
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Don't feel bad.

I honestly believe, having done about 15-20 "little six" timing belt jobs that 1 tooth off won't hurt anything but your idle speed and throttle response. I ran one a tooth off for 20 miles back in '99, I didn't understand why it felt so torquey but had so little power when revved all the way up...

Take it back down to the TB replacement stage then start over. If you had bent valves the motor would be turning over very fast with no sensation of compression, and a possible "clack" sound. Doesn't sound to me like you've done that.
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  #3  
Old 10-25-2007, 02:46 AM
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Take the question to Diesel Discussion

Oh man, you told me about this, you were in a hurry to get to the dinner with Ernesto and me in Sacramento, right? You jumped in the Chevy Van and came right up anyway, that was awfully good of you, even after the disaster.

I still feel awfully bad about that and was going to call you up today, but did not want to bother you. I hope you are not looking at an expensive valve job.

That was the gunmetal gray sedan, with the ski racks, right? I remember it from a distance, in SF, parked on Stockton St across from the Ritz when you came to SF to visit Dee8go and me for our mini gtg.

A really beautiful looking sedan. Definately worth fixing, it is a beauty, cosmetically.

I'd bet you could get a LOT more traction with the questions if you asked here: www.bimmerforums.com That'd be in the the E30 section.

Or repost this question again, here, but on "Diesel Discussion". Your '81 300SD in your signature is all the street cred and admission ticket you'd need.
You are one of them officially already.

There are a LOT of shop owners, actual mechanics and REAL DIYers, there, in DD, and most of 'em NEVER look in this section at all. Some of them disdain the place known as OD. I frequent both.

Diesel Discussion is the most heavily visited part of this whole forum. Lotta those guys could help. With the time zones, it is pretty busy, sometimes even almost 24/7

Some of them in DD even like BMWs, own them, work on them and know them.

As to your 300SD, I don't know anything about its story, except
I know it's not back on the road yet, but what you have there is one of the best Mercedes, and best diesels, that was ever made.

Ever. And, white is one of the best colors ever, for the SWB W126 diesels too. Those are half million mile cars, if ever there was one.

Those fellas over in Diesel Discussion will help you get that car on the road in a jiffy. They know the 300SD down to the last nut and bolt. It is the first place I would go for help with my gas coupe, because it is the W126 bodystyle, like yours.

Some of them are really clever. "SirNik" (Nik) is a young guy, with an '84 300SD. His car has a dual exhaust system made from cyclone fence posts. Made it himself. UFB. He is from Sacramento, and I have seen the car and met him at the Diesel Drives. The car has big chromed dual exhaust tips, like some Firebird. He is pretty typical example of the Diesel Discussion guys. Guys like that give me faith that there is really hope for this country.
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Last edited by Jim B.; 10-25-2007 at 02:57 AM.
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  #4  
Old 10-25-2007, 08:17 AM
David R. Smith
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The lady who bought my '89 325i took it to one of those "we can fix anything" gas stations when the water pump(driven by the timing belt for those who don't know) started leaking. They put it together more than one tooth off, and it bent several valves and wouldn't start.

She had it towed to shop where I was working at the time, and we ended up pulling the head and replacing several of the valves and guides(they cracked when the valves bent).

It was also a good time to update the head bolts, the OE head bolts are known to have the heads break off without warning and the loose piece eventually gets under a camshaft lobe..... very expensive at that point.

A vacuum gauge will halp you diagnose the bent valves, a fluttering needle is a good clue. I wouldn't pull the head until I knew for sure that the valves were bent, even though it's possible it happened.
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  #5  
Old 10-25-2007, 11:26 AM
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Did you rotate the engine manually or with the starter? I don't think manually rotating the engine could bend valve unless you've been working out recently.
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  #6  
Old 10-25-2007, 11:34 AM
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Quote:
Originally Posted by kerry View Post
Did you rotate the engine manually or with the starter? I don't think manually rotating the engine could bend valve unless you've been working out recently.
I agree, If you turned it by hand you would come to a point where it would get hard to turn, very noticeable hard to turn any farther. Myself, I doubt bent valves.
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  #7  
Old 10-26-2007, 07:46 PM
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Good advice and good tips, all. A few things have gone down since I posted the thread. I re-upped my subscription to Roundel so I could access the tech help advisers they feature. Both said that one tooth off might bend valves. One gave me a good walk through on what I'd need to do to pull and replace the heads on a 265K car.

My parts man in Berkeley was going to do the heads for a reasonable price, about $200 plus parts. I'd need to hone the cylinders (can drop them out with block in frame, must take out support member, supporting engine some other way). I was resigned to doing it, would at least have a semi-rebuilt engine, new rod bearings, rings, and re-newed head.

Then, oh man, I had most everything off to begin the job, including exhaust pipes, valve cover, not the intake manifold yet, and I thought, maybe I should do a compression test after all. It'd be a ***** to do all that work and have the same exact noise upon completion.

So I put the timing belt back on (getting pretty good at it) and sure enough, the compression tested primo: 170 to 185 on each cylinder, odd cause the manual says 145 to 152. I've only used the tester twice, I thought, how can I check it out, then it dawns on me that the tester connects to it's hose with a 1/4 inch air hose fitting. So I took the female off of one of my work air hoses, put a male on, plugged it into the compression gauge, and plugged the other end into my compressor which has a gauge specifying 90 psi output pressure. Checked out perfect.

While I had the spack plugs out, I rotated the engine for about 30 seconds, w/o the compression tester in one of them and it sounded totally sweet, no banging of any kind.

Back to sqare one, I guess. Still don't know what that damn noise is, but I think I saved myself a lot of work and $$. It runs pretty good even w/o the rebuild, maybe I'll do that 50K from now on the next timing belt change.
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  #8  
Old 10-26-2007, 07:49 PM
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Quote:
Originally Posted by Jim B. View Post
Oh man, you told me about this, you were in a hurry to get to the dinner with Ernesto and me in Sacramento, right? You jumped in the Chevy Van and came right up anyway, that was awfully good of you, even after the disaster.
Nah, I was in a hurry to get up to Washington state for a fair I love to go to, way up in the eastern hills.

It was some 20 hours later I came to see you guys, not that I wouldn't hurry for that.

I thought to put this thread on tech help, then I read the sticky by WHunter about that, saying I should put that kind of stuff -- non MB -- over here.
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  #9  
Old 10-26-2007, 08:59 PM
David R. Smith
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You healed it, congrats.
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  #10  
Old 10-27-2007, 03:06 AM
cmac2012's Avatar
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Quote:
Originally Posted by kerry View Post
Did you rotate the engine manually or with the starter? I don't think manually rotating the engine could bend valve unless you've been working out recently.
Quote:
Originally Posted by Early Bird View Post
I agree, If you turned it by hand you would come to a point where it would get hard to turn, very noticeable hard to turn any farther. Myself, I doubt bent valves.
What? You guys are trying to tell me I'm not strong enough to bend steel with my bare hands??

I was thinking the same thing. I figured that if there was any valve to piston contact, I'd feel the crank just stop and go no further. Back in the mid 90s, I worked for a while in a BMW shop and I happened to be there when they were rebuilding a 325 head that had experienced a broken belt at speed. Oh mah God, many valves badly bent.

After I thought it might be possible that I'd bent some valves by hand, I got to thinking that if the contact was very slight, which it would be from being off by a tooth or two, the leverage would be significant, as the piston would be contacting the valve at near the very top of the stroke, when its upward movement would very small in relation to crank rotation. Plus, when you're turning the crank by hand, you have to pull hard enough to get past the compression here and there and you might not notice that you were tweaking a valve a tiny bit.

Not saying this is fact, just my thinking. If I was being paid to do a study on this, I'd go to a bone yard and find a 325 that still had belt intact and try some experiments but in the real world, I'm not likely to know for sure if one could bend a valve by hand this way.

But the point is hopefully moot at this point, because I can't imagine my compression testing out that well with any bent valves.

And, I'll have you know, I have been working out lately.
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  #11  
Old 10-27-2007, 03:08 AM
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Originally Posted by David R. Smith View Post
You healed it, congrats.
Oh man, maybe I'll learn now to do thorough dianosis before starting on major repairs. At least I hadn't pulled the head yet, thank God.

Now if I can just find that clunking sound.
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  #12  
Old 10-27-2007, 04:04 PM
David R. Smith
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Don't feel too bad, my dad was ready to rebuild the engine in his Willys Jeep because of the racket it was making. It turned out to be a timing gear bolt had backed out and was hitting the timing cover as the engine ran. The noise sounded just like a bad rod bearing and woould go away when you lifted off the gas, my dad kept telling me to quit wasting my time, the motor was shot. Well guess what? That was 8 or nine years ago, and the old Jeep is still running.


The clunking issue is an intrigue. A bad starter bendix maybe?
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  #13  
Old 10-27-2007, 04:19 PM
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Quote:
Originally Posted by cmac2012 View Post
Oh man, maybe I'll learn now to do thorough dianosis before starting on major repairs. At least I hadn't pulled the head yet, thank God.

Now if I can just find that clunking sound.
It's likely PBSASW,
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  #14  
Old 10-29-2007, 10:12 PM
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Quote:
Originally Posted by Howitzer View Post
It's likely PBSASW,
Not sure what PBSASW is exactly, perhaps power breaks steering alternator, those letters are in there anyway.

If so, that's partly correct. I found the damn noise, it was minor -- Jeez I feel like an amateur for my near major over-reaction -- I had put in a new water pump while I was at it and apparently the new one is not as wide in the 'block out to flange for pulley' dimension by a small amount, and the pulley was grazing off the vibration damper on a semi random basis.

I JB welded some thin washers on the back side of the pulley and that got rid of that.

However, today I went in to get it smogged -- wish I'd done it before this drama unfolded -- and I'm not looking good. Failed on HC and NOX, by a large margin on NOX at the 15 mph range.

I found this site on the topic, I'm going to try to track it down. My CAT is only a couple years old, but the smog guy said on the older cars you sometimes have to replace them frequently.

My parts man in Berkeley tells me that new rings and redone head could help on the passing smog scene. I'm guessing that CATs wear out faster when they're required to work harder from excess smog.

Damn, I'd hate to replace the CAT and find out the problem was elsewhere but oh well.
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Last edited by cmac2012; 10-29-2007 at 10:20 PM.
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  #15  
Old 10-29-2007, 10:19 PM
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Originally Posted by David R. Smith View Post
Don't feel too bad, my dad was ready to rebuild the engine in his Willys Jeep because of the racket it was making. It turned out to be a timing gear bolt had backed out and was hitting the timing cover as the engine ran. The noise sounded just like a bad rod bearing and woould go away when you lifted off the gas, my dad kept telling me to quit wasting my time, the motor was shot. Well guess what? That was 8 or nine years ago, and the old Jeep is still running.


The clunking issue is an intrigue. A bad starter bendix maybe?
See above for the intro -- I found it by unhooking all the belts. I was thinking that the other wild card in this drama was the water pump I'd put in. It's SOP to do the pump and the timing belt at the same time as the pump is covered up by a lot of stuff that has to come off for the belt replacement.

So I started it up and the racket was worse. The same noise but no longer random. I carefully reached down and rotated the pulley that mounts to the front of the water pump flange and the noise stopped! Eureka! The pulley was a tad out of round and it would hit one spot on the vibration damper which spins about 1/16th away, under normal circumstances. That explains the random nature of it, as they're different diameters so the point of contact came around in a semi random way -- had a pattern but a weird one.

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