Cam Carrier Scored
 

Chasing down an oil leak, I decided to replace all the front end seals, timing belt, etc... today:

This is off of a professionally rebuilt engine, with about 2K on it.

Warning: Images may be massive.

Exhaust Cam

https://www.miataturbo.net/attachmen...ine=1392327652

Intake Cam

https://www.miataturbo.net/attachmen...ine=1392327652

Exhaust Carrier

https://www.miataturbo.net/attachmen...ine=1392327652

Intake Carrier

https://www.miataturbo.net/attachmen...ine=1392327652

I've got a spare BP4W ripped apart, and I checked that one, seems to be in much better condition. But seeing as this is only the second head I've really played with, I really don't have any basis on knowing if it's good to go like that. (Good to go as in... Once I get the oil leak under load cleared up, I get to start working on the turbo setup I have had waiting in the garage for almost a year now.)


I called the guy on it, and he said if it hasn't gone catastrophic yet, it probably won't.

There were no metal bits, no paste, or aluminum in any of oil I cleared out, and there was enough oil on the carriers themselves that it isn't as if they're not getting lubricated...

Thoughts? I have a spare BP4W head (without the exhintake mod, and with serious OMFG valve seating issues) that I've already stripped, and can probably send off to get sorted if need be, but that's money that'll be coming out of somewhere else...

Any input welcome, of course...

It doesn't look terrible but that is not good at all.

And him saying what he said is almost as shady as him selling you the engine in that condition.

Looks like it was starved for oil for a bit. I'd be concerned with how your bottom end bearings look

Get a second opinion. Head looks oil starved and i'm pretty sure i DO see flakes/chunks in those pictures.

I would absolutely NOT just put it back together and roll with it. You don't want this to happen:

https://www.miataturbo.net/attachmen...ine=1392331228

It's not as bad as you would expect. Certainly not as bad as it looks in the head, at least. The cams aren't like the main or rod bearings - they don't see any axial loads, since they aren't transmitting any power. The worst they see is the loads from the force it requires to open the valve against the valve spring, which is teeny-tiny compared to the loads that the main/rod bearings see. I would want to clean up any burrs that stick upwards from each surface (cam journal and the cam itself) so there's no metal/metal interference between the two, but beyond that, it's not going to get any worse with continued normal operation as long as you take some corrective measures now.

The head that I've been using on Rover has been on four different blocks, three of which have suffered a catastrophic failure (8800rpm overrev+broken rod, throttle body screw ingestion, and oil starvation + seized #4 rod bearing + broken rod), so it has some similar marks in the journals. A few deep ones, a few shallow ones. When I first noticed them, I asked my machinist about it (this was in early 2012 when I first had the head gone through, before the first bottom end failure). It wasn't a big concern to him, he just polished up the journals and made sure there were no burrs on the cams to be concerned about.

The cams are a little more concerning - I would have them looked at. If they can't be polished out, just swap them with anther stock set that looks a little better.

How do the other caps look?

How does running your fingernails over it feel?

He's gonna be able to feel those for sure.

Didn't see an issue with the other ones.

Re: Fingernail:

Of course I ran my fingernail over it, presenting a finger-naily tactile surface issue like that is like throwing a cooked ham to a chubby kid at fat camp... That ham 'gon get rubbed real good...

Intake Fingernail test: not really too bad, could feel it catching a bit, but more like a skip than a full stop...

Exhaust Fingernail test: Yeah, I felt that pretty good, could probably notice that one using my thumb to be honest.


Only issue I've had with the car is (WAS, hopefully) it deciding to puke oil somewhere under "spirited" driving, and it was just simply gone without a trace... :confused: Think I narrowed that down to the CAS, but decided to change the cam carrier and front main seals just in case. That's when I found ^^^^

And please don't misunderstand; the builder has been absolutely brilliant. I don't think he has any issues with me making it his problem.

He's just currently 2.5 hours away, and I'm using the MX-5 as a daily while the mundano... mondeo is hard-parked for road tax.

FYI, it does not cost that much to have a camshaft fixed if you have a damaged journal. It is still probably cheaper to source another used stock camshaft, but for those that have aftermarket cams, it is not so painful.

take some 600grit sand paper, or a stiff scotch brite pad, and polish up the journals in the head. So nothing is sticking up. clean it up good after with acetone or something like that. I always use some sand paper and break the edges on the journals and caps, they are sharp as hell.

The cam i would swap or take to a engine shop and see if they can micro polish it (same as the do to cranks)

Everyone is discussing effect, how about cause? Was the timing belt too tight?

Cause was established in posts 2 and 3. The head that I have with similar damage was also starved for oil in its life. Timing belt tension wouldn't be nearly enough to cause this.

Usually what this is is bad clearance/lubrication so as soon as one part catches it rolls into a tiny ball and scratches up everything. You have to find that one part that has a sharp point poking out and grind it individually otherwise by the time you sand it down with a big sheet of sand paper you'll sand the rest of the parts too much.

One big issue i see is if you send this off to get ground down it will take quite a bit to grind it out. To make it worse there will probably be runout from the centers.

I wouldnt be surprised if the engine wasnt lubed when put together so for the first whatever minutes it was ran dry. 10-20 seconds at 2k rpm until the bearings are fully pressurized without any lube would be enough to over heat the metal and turn a spot into a ball.

Just to add to this theory - If you end up taking anything to it I'd recommend a light scuff pad and go against the grain of cam journal so you're not making the low spots lower. Then use a good berak-in oil for the first oil change. Something low detergent and high in zinc or ZDDP.

This will allow the cam to seat, creating it's own new contact surfaces. Just keep in mind you're taking off material no matter what you do (even polishing it).

lol at the -1. I only did this for 7 years as a day job..what do I know.

Received an email back from the builder earlier today, apparently a lot was lost in the translation on the phone, because he said "Oh, that's not good", which, when dealing with a guy who's been doing war with engines for his whole life... is saying that it, indeed, is not good.

So, one phone call later, and tomorrow I get to pull the engine, run it down on Monday, and we'll spend the day going over what's borked, what isn't, what needs to be done, what doesn't, etc...

I may have to sacrifice my old BP4W head for it (it's in bits anyway, and I really wasn't working on it), but hey, recycled parts put to good use... I'm going green!

cd..

That's not how cams work.

...Well put?

These aren't my words of advice, I do however trust my machine shop. I'll pass along your in depth thoughts though :cool:

Would you care to explain how a hardened iron camshaft, rotating inside an aluminum journal won't change the surface of the journal? If I'm reading correctly it sounds like you think otherwise. Again this wasn't a theory I came up with and I'd personally love to hear the counter explanation.

Might be a question for Mr.Keegan. I wouldn't say I'm qualified to argue either side of this but I can at least explain the advice I was given.

Well, the good news is I ruled out the rear main seal as a potential oil leak.

The bad news is now my car doesn't have an engine in it...

So what do you plan on racing with? Hopes and dreams? :fawk:

It rides on oil, just like every other bearing surface in the engine. If it's changing the surface of the journal, you have a big problem.