timing belt rumor

e30fr3@k

e30fr3@k

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ok, so the E30s, as you hopefully know are built with rubber timing belts. they are supposed to last from 50-60 thousand miles. what i've heard is that if the timing belt breaks, you have to have your engine rebuilt. or the engine breaks and can no longer function. this sounds a bit extreme to me, and i would think that BMW would have found a way around that. save me from replacing my timing belt prematurely if the worst that could happen is being stranded on the side of the road for a while.
 
vlad

vlad

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Nope, what you've heard is just about true. If the belt breaks, the pistons can impact the valves. And if that happens, you will need a rebuild. There is a very slim chance that if the engine is shut down quick enough after a timing belt break, lesser damage would happen.
 
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bichmgnt

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#5
When the belt breaks there is no shutting off the engine, the engine is off. It's not firing anymore because everything is out of sync. If the car is in gear going down the road the valves will get messed up guaranteed. At 1800 RPM the pistons are pumping 30 times a second. Pushing in the clutch to disengage the engine even if it takes a blistering half a second, the valves got pummelled 15 times. Even at idle, lets say 600 rpm, each piston is is going up and down 10 times a second. If the engine keeps moving for a quarter second the valves still get hit. The engine has to stop completely in less than a 1/10 of a second in order for the valves to be good. Of course, when you try to start the engine after the stall the valves get taken out anyway.

The best you can hope for is that the bottom end doesn't get damaged when the pistons hit the valves. At that point all you need is a reconditioned head, a bently manual and a decent set of tools. I did the repair in my garage when my belt broke in "93 and it cost a total of $600 which included the tow to my house and the manual. I've heard that pistons can be damaged when this happens but mine were ok.

Steve
 
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bichmgnt

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Generally all you replace is the valves. It's all the related work to make sure all the cylinders are identical that elevates the head to reconditioned status. The valves that get replaced have to be ground and seated and you might as well do them all so they are all the same. Also the valve guides should be checked and knurled or replaced if necessary. The springs would probably be ok and I'm not sure how they get checked but if possible they should be. The cam and bearings are checked while it's apart to make sure they are still within spec. The head itself needs to be checked to make sure the mating surface is flat.

The whole point is that you don't want any problems with the head once you put it back in. If the pistons look ok after removing the head and the cylinder walls are smooth the bottom end should be ok.

The book says replace the belt and belt tensioner at 60k miles. I now replace at 50k. And even at that the belt has come out with some damage to it.

Replace the belt and spark plugs every 50k, change the oil and filter every 3k, adjust the valves, change the coolant, and replace the air filter once a year and your engine will outlive you.

Steve
 
e30fr3@k

e30fr3@k

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#9
belt tensioner? the hell's that?[scratch] ok, i know i'm due for an oil change in 2k, i'm going to do my timing belt, but what is the belt tensioner? i'm also going to put in a new thermostat which will involve emptying the coolant. and i suppose i should replace my spark plugs at the same time. now, regarding the valves, how do i know when i've adjusted them properly? i think that may be the source of one of my wierd noises. i've owned the car for just over a year and i haven't "adjusted" the valves. what does this mean exactly/how is it done.
 
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bichmgnt

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#10
First, How many miles are on the car? It's likely the timing belt has been replaced already. Check for a sticker on the fuse box or the Air Flow Meter. It may tell you the belt was replaced only 20k miles ago and replacing would be unnecessary.

If you can't find a sticker that says when it was replaced you should go ahead and replace the belt and belt tensioner. The tensioner is a wheel and spring combo that keeps the belt at the right tension and must be replaced with the belt.

But the first thing you should do, if you plan on doing any maintenance like this yourself, is get a Bentley manual. They cost about $35 and are worth every penny. It will tell you everything from how to adjust your valves to rebuilding the transmission. Don't bother buying the Haynes manual.

The manual will tell you to remove the radiator to change the timing belt but you really don't have to. It does make it quite a bit easier, and if you haven't done it before you should probably do it so you can see what you're doing. And if you have to drain the coolant anyway you might as well do the whole procedure. Besides it'll be a good experience. You may decide that it's not worth the hassle next time and pay someone to do it. I think I paid $165 including parts to get it done but I'm not sure.

Valve adjustment is easy. All you need is a couple wrenches and a feeler gauge. The rocker arm has an eccentric cam that is used to adjust the gap between it and the valve stem. You basically measure the gap when the valve is closed and if it needs adusting the bolt holding the cam in place is loosened, the cam is adjusted and then secured in place again with the bolt.

The book gives all the specifics but you may be able to find the procedure online in a technical paper section of one of the other BMW forums. But get the book. It's invaluable if you do any work on your own car at all.

Steve
 
e30fr3@k

e30fr3@k

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#11
thanks for all the info. i got a bently, but i don't trust myself anyway[rofl] perhaps it's time i grow some balls...the car now has 204 k and i just realized there is a sticker on the air flow meter. i just never looked at it. but always wondered what the hell it was. man i HATE being out of town...and steve, when you said

"The manual will tell you to remove the radiator to change the timing belt but you really don't have to. It does make it quite a bit easier, and if you haven't done it before you should probably do it so you can see what you're doing. And if you have to drain the coolant anyway you might as well do the whole procedure. Besides it'll be a good experience. You may decide that it's not worth the hassle next time and pay someone to do it. I think I paid $165 including parts to get it done but I'm not sure."

does "timing belt" mean thermostat? because i couldn't imagine that i would have to drain my coolant to change my timing belt.
[thumb]
thanks
 
Kirby

Kirby

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#13
I actually had a vehicle that had the timing chain STRETCH believe it or not. It was a 83 S10 GMC Jimmy with the 2.8L V6 they put in millions of cars & small trucks. After about 50K miles it was running like crap, developed a valve tick, and would backfire & sputter when you let off the gas at highway speed.

WhenI rebuilt the engine I discovered that the timing chain had no tensioner and I could move it about 3/8" between the gears. I could turn the cam about 3 degrees with that amount of chain slop!!! What a POS engine!!
 
jrt67ss350

jrt67ss350

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#14
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#14
Kirby,

Oh, I believe it. Timing chain stretch was one of the many, many problems on those 2.8L V-6 engines. They were horrible, horrible engines and had nothing but problems.

When I tore apart the 350 in my Camaro, I discovered that the engine still had the original timing chain in it. Someone had put an Edelbrock cam in the engine, but didn't replace the timing chain. [boxface] It had about a half an inch of slop in the chain! No wonder I was having so many valvetrain problems - two of my rocker arms had mysteriously broken in half. So, I replaced it with a Dynagear true double roller timing chain and put a new CompCams cam in it. [:D]
 
L

ldzpstnr

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#16
Now just the M10 318i's have timing chains. Not the later m42 318is. Those have belts also I believe.


I have done a lot of research into modifying the m10 four cylinder and some places recommend either buying an adjustable cam gear for them or running a timming chain that is a little stretched to retard the cam timing a little bit. Retarding the cam timing gives any car more top end power and takes away bottom end torque. Now advancing the cam timing does the reverse.


FYI

Later guys.
 
B

Big Daddy

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#18
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#18
ldzpstnr said:
Now just the M10 318i's have timing chains. Not the later m42 318is. Those have belts also I believe.


I have done a lot of research into modifying the m10 four cylinder and some places recommend either buying an adjustable cam gear for them or running a timming chain that is a little stretched to retard the cam timing a little bit. Retarding the cam timing gives any car more top end power and takes away bottom end torque. Now advancing the cam timing does the reverse.


FYI

Later guys.
Click to expand...
No, I have a 91 318is, M42 motor and it is a timing chain!
 
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