cam scaring??

[thebuddrik]

I made a post recently about a burnt valve. Well low and behold ounce I removed the cams and bearing caps I found that they are scared. The head looks fine. Sorry if this is a dumb question, I tried searching with no results, but do I have any options with the head besides a PAPERWEIGHT?!?!

 

[starscream5000]

Macro pictures of the scarring would help please. It may just be the soft babbit material that is coated on the cam saddles from the factory, but we won't know until we see some pictures. Don't try cleaning or removing anything off of them until we see exactly what it is you are talking about.

 

[thebuddrik]

I can kind of feel them with my fingernail. I dont know if that makes a difference. I know that this head has been off of the car before. It had a metal H.G. when I took it off.

 

[starscream5000]

We still need to see what it is you're speaking of before any good advice can be given .

 

[thebuddrik]

the cap looks worse than it is

 

[williamb82]

normal sadly. what happens is people dont let the spring on the tensioner for the timing belt tighten the timing belt. they think its better to pull it tighter so it causes that. usually just the front 2-3 caps on each cam. geeeting ahold ofa head that isnt like that is hard. but i did get ahold of 2 somehow. lol. always only let the spring generate the tension for the timing belt and you should be fine.

 

[Rennat]

how would the timing belt tension have anything to do with that? thats just about metal on metal with DIRTY oil... a machine shop can polish those cams and make em look brand new (as they did mine just the other day) and the caps can be cleaned up with a piece of 1500 Grit sand paper.

and getting a head thats not like that is REALLY REALLY hard/lucky... i got one. but i has no caps. so yeah... if you ever buy a head, make sure it has the caps!

 

[thebuddrik]

My head is beautiful, it is just the cams and caps. So I assume I can do that an then check the clearance , right?
is there any way to know what the clearance will be before I spend the money at a machine shop?
thanks

 

[williamb82]

they can machine the cams then machine the caps then line bore the saddles to bring it back to spec. its not cheap though.

 

[Figit090]

how could excessive timing belt pressure do THAT? Maybe the frontmost bearing but...to more behind it? i'd imagine you'd need a LOT of extra timing belt tension to even hurt one...

but i dont know.... it just seems odd to me.

 

[williamb82]

i did say usually only the front 3 caps are scored. the cam rubs the head then metal spins around and scores the caps as well. never seen any caps scored on any head but the front 3 myself. and ive been inside prolly 70+ 7m's from my own, pther peoples cars and pulling the shims at the junkyard so i have my own exstensive collection for valve adjustments.

 

[Figit090]

70? yipes!

ok i think i believe now. maybe... does the TSRM say much about tensioning? i dont remember a lot of warning in there, and just made sure i had proper slack in the belt between the timing gears.

 

[starscream5000]

a machine shop can polish those cams and make em look brand new (as they did mine just the other day) and the caps can be cleaned up with a piece of 1500 Grit sand paper.

That's just going to make things worse.

they can machine the cams then machine the caps then line bore the saddles to bring it back to spec. its not cheap though.

That's the right way to do it.

An honestly, how is the timing belt being too tight going to cause scoring on the first 3 sets of cam saddles?

 

[Rennat]

im still LOL so bad about that timing belt comment....

i know taking a piece of 1500 to it isnt PERFECT. but its better than nothing... theres quite the specefied range for the clearance for the caps.

and in order to line bore the saddles is going to cost more than you'll EVER be willing to spend on a supra head.

 

[williamb82]

you think those cams cant be pulled down into contact with the head? you make the belt too tight, then whe nthe crank starts spinning it pulls the belt DOWN which puts more load on the cams etc.. its what ive seen in person. watched a guy do his belt that way and had a perfect head. then like a month later we were pulling the cams to swap shims as the engine was then broken in. guess what, his first 2 caps on each cam were scored. intake was obviously worse. dont beleive what im saying, i dont care. doesnt bother me either way, but just letting you know, put the belt on properly, hook the spring up then tighten the tensioner without trying to put extra tension on it is the correct way to do it. thats why the spring is there. once you tighten that bolt to the tq which i beleive is 34lbs it isnt going to move so the spring could be taken off if you really wanted.

 

[Figit090]

i'm curious why one couldn't hand polish the bearings, very carefully. Unless polishing them unevenly by doing this, even in the slightest could hinder oil distribution. the tolerances are pretty tight...

I could see someone with some polishing compound and a drill with a polishing brush making them nice however... bolt them up so the seams are polished evenly...

 

[williamb82]

its called clearance. as you polish the am and journals you remove material and increase the clearance. also, you arnt gonna make it perfectly round as it needs to be. the machine shop will have to turn the cams, mill the caps, then line bore the saddles. thats the only way to fix it right.

 

[starscream5000]

More clearance, less oil pressure = not so good. The material from scored cams are also going to make their way throughout the motor, also to the main and rod bearings = not good at all.

 

[Denash]

I would check the oil pressure , if its to low it could do that.
Check it using an external oil pressure guage.
That looks like oil pump failure to me!!!

Deen

 

[thebuddrik]

Aw guys. Yall are making my head hurt. I know how to put on a timing belt, I just need to know if it is cost effective ,for a stock car, to fix the head or buy a new one.
Thanks