Seized exhaust cam

I posted this over in the 308 section without response, so reposting here.

Last week, I dropped my 79 308 GTS at a local independent Ferrari shop. The guy has a very good reputation, and has been excellent to deal with. I can tell he is an honest, hard working and competent guy.

Good news at first, he did a leak down and reported excellent results, and said the rest of the motor/trans was tight and look like it has been totally rebuilt in the last 5 years, which confirms what the PO told me a few years back when I bought the car (no records, but the PO bought it from a Ferrari mechanic I know – long story).

He called me yesterday and said that after putting things back together he started the car, and it ran for 1 minute, then he heard a bad sound and shut it down. It turns out the exhaust cam on the rear bank froze up and bent the exhaust valves. Good news is cylinders are ok.

The exhaust cam journal is all scarred up where it locked up, see pictures below. What could have caused this? We squired solvent through the cam and it squirted oil out all holes easily without pressure.

Also, it looks like at some point the head was repaired in the same spot on the opposite side (intake) cam journal – it’s been welded up and ground down.

Lastly, the mechanic was puzzled by the fact that the journals and caps were honed, and that some of the intake side journal caps are not the caps that came with the original motor (original stampings were ground off and new stampings put on to match locations). He speculated that when repairing the journal on the intake side, they honed the whole intake side. But why hone the exhaust side if it wasn’t repaired? Would that be normal? Sorry if that is a stupid question, I am a not a great mechanic.

One last unrelated question, it looks like the existing valve stems are honed with a criss-cross pattern – he mentioned that is not the way the valves come – what is that reason for doing that?

Well anyway, it looks like I will have ½ of a valve job as a result, and with back head off you can really see how clean and tight the car is – its nearly spotless and everything looks nearly brand new – he said everything on the car was rebuilt in the last 3-5 years, so that is good news.

He says it’s his fault so I don’t have to pay for it, but I feel bad because he is a small independent shop, so I might chip in to pay for the parts or something.

Any insights from the experts would be appreciated.

- Geno
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Sounds like this was a fire engine that was repaired at some point.

If he's pulling the head make sure he checks the areas where the head nut/washers sit on the head. On most fire motors I've seen this are was f'd up so I machine material out of there and made steel inserts. On one motor this was the case even though no repair of the cam caps was required so watch out.

On high mileage unmolested motors I've seen practically zero wear on the cam caps FWIW.

Cheers,

Sean

 

Sounds like you got the head off ... make sure the oil passages aren't plugged in the head itself. Make sure someone didn't install a solid dowel pin in the block for the lube dowel that feeds oil to the head.

The crosshatch on the valve stems is probably someone just scotchbrite/polishing them in a lathe or something. I do this on everything I put together so I can see the wear pattern when I take things apart at a later date.

Cheers

 

Thanks for the replies. What would cause the cam to seize like that? and forgive if this is stupid, but wouldnt alot of force be required to stop the cam from spinning?

 

Looks to be the furthest cam journal from the oil supply. The damage doesn't really look as much like oil starvation as it does like mis-alignment. I'm not sure how that could happen unless perhaps someone was checking cam timing with the old "matchbook cover under the bearing cap trick" and forgot to remove the matchbook. If it was oil starvation I would expect to see scoring in a few places before anything seized up, and maybe some heat damage on the cam journals.

http://www.ferrarichat.com/forum/showpost.php?p=136693584&postcount=39

 

Yes it would take a lot of force ... either the cam is bent or the cam caps weren't line honed properly. Have you put any miles on this motor?

 

Hmm ... from first post sounds like she was running and driving just fine so I would place my bet on "mechanic mixed up cam caps" perhaps? Might be why he's willing to give you a break on the repair. From memory though seems like the end caps are unique from the center ones so kinda hard to mix 'em up?

 

Make sure you got stainless exhaust valves why you're in there!!!

 

the engine was reportedly rebuilt a few years ago, then sat for a couple of years with minor use. I have it two years, and drive it every weekend, and yes it was running fine when I brought it in.

the cam caps on the exhaust side look all original, but on the intake side (where there looks to be a prior repair on the journal furthest from the oil supply) are not original, the stamped numbers have been ground off and new numbers stamped on).

just out of curiousity, why did you suspect engine fire? replaced journal caps = some melted? i am heading over there today again, if i remember only one of the journal caps is not original, and its an inside one i think

thanks for all the help

 

I think all the journal caps are unique, not necessarily in general shape, but i was told when them manufacture the engine, the bore the journals/endcaps all assembled, then dissassemble and put the cams in, that way there is a perfect fit, and that is why all the journal caps are stamped with a number, with a corresponding stamp on the head.

 

I just suspected fire 'cause I don't see any other reason to replace cam caps unless lost?

Even if there was a bunch of wear you trim the flat surfaces of the cap and re'bore/size just like a connecting rod.

Look at the area where the head washers sit and make sure it doesn't look depressed from the washer.

Deburr where she seized and put the cam in by hand with all the caps and see if she turns freely.

The end caps see the most damage from fire from what I've seen.

Yeah the cam caps are "unique"/numbered and specific to each location but the center three can be swapped if a guy's not paying attention which you're assuming your guy is. Now that I think about it the end cam cap could've been put on in the right place but backwards. Did you see it at teardown? I remember seeing a rod cap that was put on backwards and the inteference was on opposite sides ... I'll explain what I mean if you want but that might make enough sense to you.


Sean

 

If you mix them up or use a cap from a different engine it is possible to bind up the cam (I have seen engines with mixed up caps that worked okay). Because it ran fine when you brought it in makes me suspect that something happened at the shop. A couple possibilities have been suggested but it's hard to judge over the internet. The fact that the mechanic is fixing it is good, stay with that. If you want to give him the benefit of the doubt and make a contribution towards the repair okay as well.

 

Your pic looks like the cap was on backwards like the connecting rod I saw.

 

I agree, a mistake was made.

 

Sean, thank you.

I get everything you are saying except

"Look at the area where the head washers sit and make sure it doesn't look depressed from the washer"

i remember the mechanic saying that there was something odd/different about these things that look like guides to me, said some were sitting lower than the others. is that what you are referring to?
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While replacing the cam seals/valve adjustment, i mixed up a cap and the cam didn't want to turn. fortunately, i caught this and double/tripple checked all caps.

Sorry to hear about this.
chris

 

I am heading to the shop now, i will take a picture to see if the cap was on backward, but it looks like sean can tell that it was from the picture above.

 

Those are the locating dowels that hold the cap in precise alignment. If they're missing, it's possible for the cap to be a little "off" but if the cam is in there (has to be) when you tighten the nuts, it probably wouldn't bind up. If the dowels are in place and you put the cap on backwards, they will force it to their alignment and probably bind the cam.

 

I'm talking about the actual nuts and washers that secure the head to the block ... look down in that area.

 

I have been told that if a head has been warped, and in need of resurfacing, the bores are no longer straight. Its correct, I believe, to bore both exhaust and intake to correct this.

I don't have any first-hand experience with this kind of failure and wonder why the scrape marks are diametrically opposed from each other. Is that because the scraping on the block half of the journal caused the clearance to close up on the cap half of the journal or vice versa?

 

It's because the cap was put on backwards and didn't line up with the block.

 

So the backward installation was done AFTER the line honing had been done?

 

that's what it looks like.

Poster mentioned one cap had been replaced or something ... maybe this cap was off another head and lined up better "the other way" meaning numbers not on outside? ... just a guess since this is a pretty fundamental thing to get right. Engine in the car not so easy to see on front bank but NO excuse ... if the mechanics reading this post he'll punch the numbers on the opposite side and he's got an excuse LOL.

Cheers

 

i just came back from the shop, and snapped this picture. this is with the end cap in the correct orientation (stamped numbers facing out), and you can see the scar marks are out of alignment. if you put the end cap in the incorrect way, the scar marks align perfectly. i am not a mechanic, but i dont see how the scar marks could have been created with the cap in the correct way. That, and from what others have said, it look like the cam bound up bc the cap was in the wrong way. Would you agree with this. Mechanic was adamant it was put in the correct way.
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You have your answer. Don't fight with him, just get it fixed right.

It looks like the damage to the cap is pretty minor (clean it up with a file and it's probably good to go). You could have the bearing caps all line-bored. What's important is that the bent valves and broken belt are fixed.