M42club.com - Home of the BMW E30/E36 318i/iS
DISCUSSION => General Topics => Topic started by: nomad on August 21, 2007, 11:42:31 AM
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So how does one tell if the chain has stretched or the cam gears are worn out? These seem to be ok, they look uniform etc.
The chain guide rails look really good to my untrained eye.
Any input?
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Red X usually mean they are shot! ;)
Take a look here:
http://www.m42club.com/forums/showthread.php?t=2892&highlight=timing
and try reposting the images.
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I'll repost the images and put them up again.
Mine look like the slightly pointy ones. I'll call and get a price but I may have to button everything up as is till I get more cash.
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If the teeth are sharp, they are toast.
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I can see the images fine here at work and at home.
Mine look like the slightly pointy ones. I'll call and get a price but I may have to button everything up as is till I get more cash.
You can see them because your system has them loaded into cache.
They are stored in a non extension format, meaning they need to be tied to the original page in order to render. Your system has them in cache, so it already knows how to render them.
As for the parts...
Be prepared to replace guides, idler, lower sprocket, cam gears, chain, and tensioner. The only optional in there, is the guides, you MAY be able to re-use them. If not, bend over.
Don't forget the gaskets, oil, filter, coolant and thermostat. All should be taken care of at the same time.
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I'll think about adding that to my toasted head parts list.
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I just bought a set of guides from autohausaz. Not too terrible of a price. About $150 IIRC. I did not realize it until I received the new ones, but the insert in the guides is a high density rubber compound. It is soft enough to give when you poke your fingernail in it. The only ones that I had seen before looked really good, but were hard like plastic. Probably close to their end time. Had I not seen the new ones, I would have re-used the old ones.
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Thanks everyone. I've got to weight the cost to necessity value. I can certainly do the timing chain next year if this works out.
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And look at all this crud in the intake runner. I've got to clean this up!
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And look at all this crud in the intake runner. I've got to clean this up!
That doesn't look too bad. Mine looks worse @ 98k.
I agree on the gears...they look worn.
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Yeah I agree the cam gears look worn. As owner of the "pointy ones” in the other post, let me try to explain why yours look worn.
1) Pointy teeth do not necessarily meant sharp teeth. My pointy teeth were not sharp and still had flat tops.
2) As a chain stretches it places stress unevenly on the gear teeth and deforms the tooth profile. You will end up with a hook shape as the valley of the tooth becomes elongated. This is pretty evident in the first picture you posted. If you look at my cam you will see a more uniform shape and wear profile in the teeth valley.
3) You can measure chain stretch with a tool or with less accuracy with a ruler; however you need to know the standard length for a number of links for a new chain. (I don't know what this is in the M42) If there is any meaningful stretch it doesn't matter what your teeth look like you will be toast soon.
Ignoring general wear which uniformly loosens things up, hooked teeth come from chain stretch which comes from stress. I don't know if there is enough mass in the head to create much of a load, but it’s pretty easy to understand how hard acceleration is going to unevenly load the chain versus smooth acceleration. So style of use certainly affects the degree of chain stretch and thus the wear on the gears.
On my car timing chain and gear replacement is high on the priority list mostly because of oil ooze from the lower timing case sufficient to cause overnight spotting, and evident, if not excessive, wear.
The link I posted above has the link to the cam gear at pelican parts in the last post
Brendan Purcell's page has the best DIY on changing the timing gear that I have found: http://www.esatclear.ie/~bpurcell/318istimingchain.html
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1) Pointy teeth do not necessarily meant sharp teeth. My pointy teeth were not sharp and still had flat tops.
The flat top missing is exactly what I was reffering to when I say sharp/pointy teeth.
If the cam gears are worn enough to remove the flat top, the idler and sprocket are way worse.
3) You can measure chain stretch with a tool or with less accuracy with a ruler; however you need to know the standard length for a number of links for a new chain. (I don't know what this is in the M42) If there is any meaningful stretch it doesn't matter what your teeth look like you will be toast soon.[/QUOTE] Pointless unless you know the pitch.
Ignoring general wear which uniformly loosens things up, hooked teeth come from chain stretch which comes from stress. I don't know if there is enough mass in the head to create much of a load, but it’s pretty easy to understand how hard acceleration is going to unevenly load the chain versus smooth acceleration. So style of use certainly affects the degree of chain stretch and thus the wear on the gears.
Not entirely true.
I have seen plenty of other sprockets that do, and these could at some point during the wear cycle, but at some point they stop hooking and change to a point.
None of my sprockets were hooked.
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Great post. Thanks! Very helpful.
I'm going to price it out, chain is around $55 and with gears i'm thinking about $200? Once I see the condition of the head I'll see if I can afford this, or wait another year. I won;t be driving it too much after this fix.
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Look for the parts of Pelicanparts.com. They have pretty much everything, and it seems to be pretty cheap.
BTW the idler gear probly doesn't need to be replaced due to the fact that it is not taking much load. Even if it looks bad it probly has a lot more life. The crank gear, on the other had, needs to be replaced. Also, don't forget the crank seal.
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Pelican didn't list the cam gears when I looked. Guess I'll have to call.
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I have the cam gears and chain I pulled out of my motor when I redid my timing chain that I'll let you have for $60 shipped to your door. Extreme close up in this thread (http://www.m42club.com/forums/showthread.php?t=1224), but they are really pretty new looking.
I replaced them because I had no idea when/if the timing chain had been done. Once it was all apart (and I already had the new parts in hand) it became apparent that the timing chain and cam gears had been done in the not-too-distant past. I went ahead and put my new parts in, but I still have the gears and chain.
Had I not already had the new parts on hand, I wouldn't have hesitated to reuse the cam gears and chain. The idler and crank sprocket needed to be replaced, but these look good to me...
LMK.
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PM sent
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Pointless unless you know the pitch.
Not entirely true.
I have seen plenty of other sprockets that do, and these could at some point during the wear cycle, but at some point they stop hooking and change to a point.
None of my sprockets were hooked.
I didn't know that. That does bring a better understanding to what "pointy" means.
Please explain what "pitch" means in this usage. Is there a way to measure chain stretch?
Thanks for the clarifications. I've appreciated your other posts and have much tighter upper oil pan bolts thanks to your cautionary tale! :)
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I didn't know that. That does bring a better understanding to what "pointy" means.
Please explain what "pitch" means in this usage. Is there a way to measure chain stretch?
Thanks for the clarifications. I've appreciated your other posts and have much tighter upper oil pan bolts thanks to your cautionary tale! :)
Pitch is the distance between each pin on the chain. As the side plates stretch, this measurement changes. Even if you know the pitch, you still need to know what constitutes too much stretch. Some stretch is normal.
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Pitch is the distance between each pin on the chain. As the side plates stretch, this measurement changes. Even if you know the pitch, you still need to know what constitutes too much stretch. Some stretch is normal.
Indeed # of links for a given distance is how I have measured stretch in the past. Basically count the pins and know how many add up to a certain fixed distance. I hadn't heard is called pitch before - Learn somthing every day!
Thanks
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(http://www.m42club.com/forums/attachment.php?attachmentid=1472&stc=1&thumb=1&d=1187846656)
Those cam gears need to be changed along with the chain. They are very worn out. This is how mine look after 140k miles. The top of the gear teeth need to be flat. They get sharp like that after the chain gets loose and starts to wear away the teeth.
(http://farm2.static.flickr.com/1320/1244277034_d679884644_o.jpg)
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tjts1 is right on. Sharp teeth mean they are worn out and due for replacement. The pic he posted is how they SHOULD look.
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I would strongly recommend replacing the guides. I bought an engine that had had a new chain and gears fitted but it tuned out the guides had not been replaced.
After 6 months of use on a long drive back home from Le Mans one of the guides started to break up due to them being old a brittle.