Is my cam chest toast?

[PutALittleHeatOnIt]

Opened up the cam chest on my '98 Evo today...found a small groove worn into the breather gear cylinder, looks like the cam was rubbing a bit. Small amount of metal shavings in the oil, some scoring on the breather gear cylinder. Too end looks fine, lifters and blocks have a small amount of scoring but nothing that will catch your finger. Anyone run into this before?

[JBinNC]

If you can see ANY metal in the oil in your cam chest, you have a problem. Something in the motor is shedding metal, and you must find out what it is.

That being said, scoring in the breather gear bore is normal for motors with the stock nylon breather gear. Not desirable, but normal.

Here are some candidates for the metal you are seeing, roughly in order of possibility:

Tappet rollers - any radial play that you can feel equals a bad roller, and this is VERY common in evos.

Inner cam bearing - the stock INA bearing is prone to failure. You will see a worn or spalled cam journal as evidence.

Bad rod big end bearing - not as common in evos as in earlier motors, but a '98 is 24 years old now.

Bad pinion shaft bearing - this is more common in the '80s evos than in the '90s models.

If you don't find evidence of one of the first two possibilities, you will have to do a complete motor tear-down to check for the last two.

Metal in the oil will usually cause damage to the return side of the oil pump, requiring replacement.

Jim

[PutALittleHeatOnIt]

Thanks Jim. It looks like the metal is coming from a small part of the breather bore where the cam was rubbing. Inner cam bearing looks intact, but will be replacing anyway. Also planning on new lifters. I will try to attach a picture

[JBinNC]

The cam should not touch any part of the breather bore.

Jim

[PutALittleHeatOnIt]

[JBinNC]

Ugly. The cam should never be far enough inboard to touch there. Aftermarket cam with no shim? Cam thrust plate missing? Gotta be one of the two.

Jim

[PutALittleHeatOnIt]

I saw no shims in there, new to me motor so I think that you are correct. Any chance I could file it clean and run it with proper spacing?

[JBinNC]

I saw no shims in there, new to me motor so I think that you are correct. Any chance I could file it clean and run it with proper spacing?

Good chance. That little scar is nothing. Do put a good cam bearing and a steel breather gear in it (S&S preferred).

Jim

[Dragstews]

That year model didn't use a selectable cam shim, it was made on the camshaft and only the thrust plate was used ..

If your cam is aftermarket it will need the shim installed and set to .010" end-play ...

[PutALittleHeatOnIt]

Does the thrust plate sit on the crank side or the cone side? Cam seems to be locked into the nose cone right now so I'm wondering if the thrust plate failed causing the interference with the breather bore

[JBinNC]

The thrust plate in your '98 would be a hardened washer about the size of a 50c piece, and it goes on the inboard side of the cam.

You can just tap the cam out of the cover, after removing the ignition rotor of course.

Jim

[Dragstews]

[PutALittleHeatOnIt]

It appears the problem was caused by a missing thrust plate. New plan is to upgrade the cam bearing and breather gear, obviously add the thrust plate, and most likely replace the lifters and blocks after smoothing out the scar. Thanks again guys!

[pan620]

What about all that metal that is in the motor, oil tank, lines well ever were, all needs a Good cleaning

[PutALittleHeatOnIt]

Drained the pan, nothing shiny in there, doesn't look like it made it out of the cam chest. Oil in cases looks fine too. Going to pull apart and inspect the oil pump as well