What caused this damage?

billd · 01-08-2007, 11:09 PM

Inspecting my engine after a nasty backfire that stripped my ring gear, I discovered this damage on the inside of the cam housing just inboard of cylinder 1. Is this spalling? What could have caused this damage? Can I get by with smoothing this out, or does the cam housing need to be rejected?

I also found this impression in the valve cover above the cylinder 1 intake valve. It looks like the valve adjusting screw impacted the valve cover. Something must have flexed a lot for that to have happened.

euro911sc · euro911sc's Garage

I don't think that is spalling...

I would be more inclined to say something got loose. If you look at the nut in the first image it looks like an impact mark on the edge nearest the cam loab.

Then the second pic of the valve cover somewhat confirms something may have gotten free or was in there to start. Did you find anything in there rattling around when you took the cover off? Prob. not or you would have mentioned it...

Also, striping the ring gear on a back fire seems a little off as well... must have been one hell of a back fire! Others may have more experience here than I, but if something got stuck and jammed things a bit... well that seems more plausible.

*shrug*

Maybe the culprit is jammed in there where you can not easily see it? Are all the lock nuts there? Valve lock nuts? Tappet Feet?

-Michael

billd · 01-09-2007, 03:23 PM

I suspect you are right. This looks like a nut got loose in the cam tower. That explanation also accounts for a few other scratch marks that aren't in the photo. I found no offending foreign object when I opened up the engine, but I haven't checked the sump yet. Next step.

billd · 01-09-2007, 10:54 PM

Here's a better view with the cam out. I'm planning to grind/sand/polish this down and then reassemble.

I checked the sump and there is no sign of the foreign object. I suspect it escaped either when I drained the oil, or when I pulled the valve covers.

SP2 · 01-09-2007, 11:50 PM

I looked at diagram of the lubrication system. If there was a foreign object loose in the cam housing, then it would either stay in the housing (and maybe fell out when you removed the valve covers as you said) or more likely it went into the oil return tubes then traveled to the bottom of the crankcase. It wouldn't fall out when you drained the oil because there is an oil strainer above the sump plate. The strainer would prevent it from getting sucked into the oil pump, because the inlet tube to the pump is below the strainer.

So I would think you should be concerned that the piece remains at the bottom of the crankcase. I have my engine out on an engine stand now with the sump plate off, and I would think, with the oil drained, that you could remove your sump plate and strainer and peek in there with a flashlight and mechanics mirror, and maybe fish it out with a magnet. Especially if it was a loose nut.

I just looked at the bottom of my engine and I am pretty sure you can. It seems like there are a lot of places at the bottom of the crankcase for it to hide, but you might get lucky.

Anyways, just a thought. Trying to be helpful. Good luck!

euro911sc · euro911sc's Garage

That or turn it over and hope it falls out the breather plate hole... hehehe

-Michael

Rod Schneider · 01-10-2007, 07:04 AM

I'd also be concerned with whatever caused the damage in the first place. Somewhere you have a broken or missing piece that needs to be addressed. Are all the head nuts in place?

MBEngineering · 01-10-2007, 07:38 AM

HI could we have a photo of the inlet rocker please, top and bottom. who has had the engine apart??

thanks, regards mike

billd · 01-10-2007, 08:41 PM

Quote:

Originally posted by MBEngineering
HI could we have a photo of the inlet rocker please, top and bottom. who has had the engine apart??

thanks, regards mike

Here are four views of the cylinder 1 intake rocker arm

I bought this motor last summer. I don't know its history before that. I swapped the cams in September. Its possible that I dropped a nut in then, but I am real careful about such things - I lay out exactly the number of nuts that I need so I know if one goes missing - but its possible.

billd · 01-10-2007, 08:42 PM

Quote:

Originally posted by Rod Schneider
I'd also be concerned with whatever caused the damage in the first place. Somewhere you have a broken or missing piece that needs to be addressed. Are all the head nuts in place?

All pieces - head nuts, cam tower nuts and barrel nuts, valve adjustment lock nuts, valve adjuster "feet" - were present and accounted for before I disassembled things. Whatever it was was something extra, not something that came loose.

sww914 · 01-11-2007, 09:49 AM

Could it be old damage from a broken rocker sometime in the engine's past? It all looks like a rocker has bounced around in there to me.

euro911sc · euro911sc's Garage

I'm stumpped... what about a rocker shaft nut? I suppose one would not have placed TWO valve lock nuts on... *scratch head*

Well, got me interested in finding out the root cause for sure

-Michael

euro911sc · euro911sc's Garage

what about a piece of spring? Sometimes the inner springs break and maybe something come from one of those?

-Michael

aigel · aigel's Garage

What sww914 said. Are you confident this may not be an old wound from a formerly broken rocker arm in the engine's past? That would be my bet. The rocker you took off looks pristine. There is nothing else there that could do that sort of damage, without chewing up the rocker arm and cam as well.

George