Author Topic: Max allowable chain length on m42? (Read 6378 times)

juliea · « **on:** February 01, 2010, 03:14:42 PM »

Does anyone have the spec for the max. allowable chain length on the m42?

I'd like to see if my chain has stretched and should be replaced, but haven't been able to find the target value.

KenC · « **Reply #1 on:** February 01, 2010, 05:53:37 PM »

How can you measure it that precisely? I can't imagine it stretching more than 3/16"

Chalino · « **Reply #2 on:** February 01, 2010, 06:16:43 PM »

Quote from: KenCopperwheat;86437

How can you measure it that precisely? I can't imagine it stretching more than 3/16"

What's 3/16" in millimeters?

KenC · « **Reply #3 on:** February 01, 2010, 09:17:07 PM »

Quote from: Chalino;86439

What's 3/16" in millimeters?

5mm... and even that sounds like a stretch (no pun intended).

I'm really curious what you would use to precisely measure the chain.

flyinglizard · « **Reply #4 on:** February 01, 2010, 09:40:06 PM »

Other than hanging it on a bar, with the new one next to it, I wouldnt know either. Many shop manuals measure it indirectly with the tensioner protrusion. IE, if the shaft shows X amount, replace chain. The chain is only 96$ from Stu tho, what is the big deal? We all know that we will put way more $ into these cars than they will ever be worth. IMHO. If the chain breaks, you are looking for a new engine. Lucky for us, the guys @ BF will give you one pretty cheap. HAHA.

The crank gear looked the worst of your gears. Change that for sure . The top cam gears can be changed any time, and looked pretty good,IMHO
Good luck. MM

juliea · « **Reply #5 on:** February 04, 2010, 07:14:28 PM »

Thanks - was thinking that if the spec would be between links, I could use a digital caliper....but now that I think about it, that's not really a reliable measure either....

flyinglizard · « **Reply #6 on:** February 10, 2010, 06:13:30 PM »

The chain was about 58$ from pelican. The new one and the old one look about the same, pin to pin. I can not tell any difference in lengnth. I have no idea how many miles on this chain. The car reads 250k and the odo does not work...
The 4 hole guide, seems to be the bad part that wrecks these engines.from good sources.

MM

Choking Hazard · « **Reply #7 on:** February 16, 2010, 10:40:18 PM »

I finally got an un-cracked head on, and Im putting on a new t-chain at about 260K miles. My old one looked fine, but when I put in the new one it was substantially tighter. I don't think the tensioner will deflect it very much any more.

What "4-hole guide"?

flyinglizard · « **Reply #8 on:** February 17, 2010, 07:23:27 PM »

The driver sid e guide has 4 holes. The tensioner side has 2 holes. The 4 hole slide breaks up and causes the cam/crank wheels to jump timing and ruin some valves. Supposedly the chain wont break unless the guide breaks and jams the chain.
Racing the M10, we always took out the double chain and used the single. never broke the chains,just rockers. Shame that BMW uses the chain instead of the belt for these engines.
As the guide wears, the cams gets late also, needing some advance on the cam wheels.
If you can see almost the second groove on the tensioner, the chain and or the guide is falty,IMHO.
I have had two of these in my shop in the last month. Buy the guide and chain over 200K. IMHO.