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DISCUSSION => Engine + Driveline => Topic started by: the END on February 25, 2016, 03:27:10 PM

Title: Cam's timed 180Degrees incorrectly
Post by: the END on February 25, 2016, 03:27:10 PM

Hello,
I've done a head swap and a full engine build with the m42 before, and this last time when i was changing a head, i was too much in a rush and hastily mistimed the cams. From TDC on cylinder 1 the cams are 180degrees off (dots on the lobes are pointing down). I am prepared to take it off, as i have another spare head, but before doing so, I was wondering if anybody could confirm or deny whether or not i would have bent some valves.

I didnt realize the mistake until after having it all together and trying to start it, then removed the valve cover and realized the error.
initially when trying to start, it was making a pretty bad tapping noise, i thought it could have been the lifters pumping up with oil, but now i think it could have been the valves bending themselves out of the way of the pistons. visually i cannot see.

any insight? thanks

Title: Re: Cam's timed 180Degrees incorrectly
Post by: 1998ccc on February 25, 2016, 09:26:14 PM

A leak down test will tell you.  Good luck.

Title: Re: Cam's timed 180Degrees incorrectly
Post by: bmwman91 on February 26, 2016, 05:46:35 PM

If it sounded like a diesel engine then yes, pistons and valves were saying hello. It is not necessarily true that the engine is dead though. The hydraulic lifters have enough give in them to allow the valves to withstand a little bit of interference. I had my timing off by a few teeth once and drove around the block thinking it was a sticky lifter making the noise when it was actually valves hitting pistons. It went on for another 60k miles just fine.

Anyway, as suggested above, get it timed correctly and do a compression and leakdown test. Good luck!

Title: Re: Cam's timed 180Degrees incorrectly
Post by: the END on February 28, 2016, 07:00:14 PM

Thanks for the responses guys, I didn't have the equipment to perform the leakdown test, so what I did was take measurements from piston position compared with opened/opening valves, then compared those to the spare head, from the best i could tell, I had it timed just so that all the valves and pistons were just missing contact with each other. That was a relief... but i decided to change the heads anyways, for a few reasons, the spare head was fresh from the machine shop, and it was in overall better condition than the one that was on. So now i've got my good head back on the car, timed perfect, running great. I haven't really scrutinized this head which was mistimed, but the valves appear to be correct to the passing eye.

Title: Re: Cam's timed 180Degrees incorrectly
Post by: bmwman91 on February 29, 2016, 01:48:27 AM

Glad to hear that it is running.