Performance cams can destroy things

[Hallen]

This is what happens when you don't check your clearances when installing a performance cam in an M20. It turns out the head used had been shaved a couple of times and a stock head gasket was used. It was a simple mistake that almost ruined an endurance race for a team.

It is a good lesson for all of us. Scroll down a bit on the page for more pictures.

http://www.bmwpugetsound.com/vbb/showthread.php?t=38758&page=3

[SpecM]

holy crap... that head looks a little rough!

[Hallen]

Yep. They had piston to valve contact on all 6 cylinders. Pretty messy. A ruined head, ruined pistons... pretty much a complete write-off.

[mikeedler]

that had NOTHING to do with a performance cam. If the cam clearances were bad, it wouldnt have made 2 min, let alone 30 sec. of life. As well as on the pics you can clearly see the "machine to/ but not more" marks. the head still had plenty to go.

[TDE30]

^ Yup.

Like you said, the head was shaved a few times (unbeknownst to you) and the stock head gasket was used. It was a pretty simple mistake that kind of effed up the entire head. But certainly not an issue with a "performance cam."

A good learning lesson if anything.

[SpecM]

I like the Mahle filter

[Hallen]

that had NOTHING to do with a performance cam. If the cam clearances were bad, it wouldnt have made 2 min, let alone 30 sec. of life. As well as on the pics you can clearly see the "machine to/ but not more" marks. the head still had plenty to go.

There is nothing at all wrong with using performance cams. That wasn't the point. I probably said it wrong.

I think the main point is that you need to check your clearances and if using a performance cam, then double check the clearances.

This is what the owner said "In the pursuit of more horsepower, I neglected to measure the head and check for valve clearance with a new cam installed. There was contact across all 6 pistons; #2 just happened to give up bigger!"

[Rocla]

"machine to/ but not more" marks. the head still had plenty to go.

Short instructions how to read those marks please.

As long as thos areas are not plane to surface the head is not milled too much?

[der affe]

really big performance cams will destroy cheap aftermarket cat converters though. the last one was 4 months!

[mikeedler]

the sections that are circled are the "measurement" indents. kinda like a tire on a car with the TWI

as long as you havent milled farther than those marks you are in the good.



cant see why the cam would ruin a cat??? your o2 sensor is not doing its job is what is ruining the cat.

[nando]

yes M20s are very sensitive to this. Even with a stock cam, piston/valve clearance isn't very much. when you add 1-2mm of extra lift and double the lift at TDC, you're likely to have contact.

Checking valve clearance should be a basic part of ANY cam swap. you can't take that shit for granted.

out of curiousity, what cam was it?