Timing Q

[Ian Bowers]

So, the m42 has been back together for a month now, but the recent dyno run showed that the timing is still fucked.

It's an M42B18, .140 MLS, ARP Headstuds.Mark D 91 chip.
Intake and Exhaust cam are advanced to their maximum. Retarding either cam makes me lose torque, to a pretty serious extent; started with the cams dead center, it wouldn't get on the cam until 5k, and was a total dog before that.

I'm thinking I MAY be a full tooth off, which is why I'm advanced so far. I'm scared to change it, as I don't know how close the pistons/valves are as-is.

Here's the dyno sheet:


There is a serious, serious drop off at 2900/3kRPM, and it's been fucking my fuel economy on the freeway, as with my 3.73, 70mph is 3000, so I'm at 80% throttle to sustain that speed. The drop off past 5.7k seems weird to me as well.

Anyone have any suggestions? The car idles fine, doesn't have any issues, but it's dropping off heavily at high RPM, and has even less torque than normal.

Thanks guys. :puppy:

[Dj Buttchug]

aight. well this is gay. I cannot tandem with this... lol

you can move it one tooth and the vavles wont kiss. Just be dead center on cam sprocket. Hand turn the engine before you fire it. it may run like shit tho, unless of course you are a tooth off to begin with like you said.

[Ian Bowers]

aight. well this is gay. I cannot tandem with this... lol

you can move it one tooth and the vavles wont kiss. Just be dead center on cam sprocket. Hand turn the engine before you fire it. it may run like shit tho, unless of course you are a tooth off to begin with like you said.

yeah, well... Boost is coming, just trying to get it set up properly N/A first. Not looking good for sep, though. :(

Thanks bud, I'll check it out. Choose a clutch yet?

[Simon S]

I discovered a similar deal when working on my m42.. sprockets were at extreme – and my intake sprocket was one tooth off. A straight-edge on the rear cam ‘squares’ will tell you if you’re a tooth off.

Bunch of discussion and pictures in this thread.

Weird – including mine, this could be the third m42 I’ve read about where the chain was off a tooth.

[Ian Bowers]

Thanks Simon. I'll check it out with a straight-edge, but I think I did that when we set the timing after putting it back together. I do kind of remember counting 8 links inbetween cams, though.

The .140 headgasket has made everything just a little bit off. :(

[KenC]

Why not just reset the timing and go from there?

[Mr.SWISS]

What's the head thickness? If you get it too tall or short it will throw off the valve timing and therefore the ignition timing won't be right either.
Did you use the pin tool to lock the flywheel in position and the cam locking tool to time the cams? Arrows on cam sprockets point straight up, dots on cams are TDC when on top, and pin is locked in flywheel is true TDC. Adjust from there.

[tonywonder]

you are suppose to count rivets not links. 15 rivets inclusive of the ones the arrows on the cam gears point at. the cam gear arrows should be pointing straight UP. bolts should be centered and back of cams squared.

i reset mine. when i saw they were off.

http://www.r3vlimited.com/board/showthread.php?t=209205

[immajackuup]

why your powerband not smooth?? is all jumping up and down on the chart.

[Vtec?lol]

Whoa, I regret selling my M50. Where's all the ponies at yo?

[Ian Bowers]

What's the head thickness? If you get it too tall or short it will throw off the valve timing and therefore the ignition timing won't be right either.
Did you use the pin tool to lock the flywheel in position and the cam locking tool to time the cams? Arrows on cam sprockets point straight up, dots on cams are TDC when on top, and pin is locked in flywheel is true TDC. Adjust from there.

Head thickness is stock, it was perfectly flat when I removed it. Never had a profile gasket/head gasket failure, was just preventative. I have an M20 flywheel, so I can't use the pin. I did the straight-edge on the back of the cams, and had the arrows pointing up. However, the ignition timing being off sounds like it could also be a cause.

I think the main loss of power is the fact that I'm running ~8.5:1 compression due to the MLS, I was under the impression that the compression drop wouldn't be so severe.

why your powerband not smooth?? is all jumping up and down on the chart.

No clue, tbh. It's why I started the thread.

Whoa, I regret selling my M50. Where's all the ponies at yo?

They took off when they realized they sound like a raspy 4 cylinder.