Camshaft cap - sources

[Chimp871]

Whilst taking even bank camshaft out today, camshaft cap #3 come apart in 2 pieces when lifting off. There was no load.

Usual places don't offer one for sale, any ideas where to source?

[CerbWill]

Ring the usual suspects and ask? I suspect over the years a few heads have been destroyed leacing the caps intact. They're not taken from any other engine as far as I know. Try Powers, APM TVR, Str8Six, or Jody at Python Racing.

[Thom]

Aren't cam caps line-bored with the heads and each marked for their specific position?

[TwinKam]

Thom said:

Aren't cam caps line-bored with the heads and each marked for their specific position?

Yes. You'll probably have to get a cap made oversized, then machined to suit. Probably head off time.

[Chimp871]

I was leaning towards pulling the engine later in the year due to what I think is a bearing noise. I've got the interior out at the moment for a recarpet so the shim service was whilst I was waiting for soundproofing to arrive. Bit of a unwelcome surprise....

Any ideas why cap #3, the middle one, would go like that. You'd think it would be the least stressed?

I'll speak to the known experts on what they thin!.

[Jhonno]

Probably been undone badly in the past or dropped.

[gruffalo]

I am meeting up with Jason of STR8SIX later, I have a feeling he has some old scrap heads knocking around and will see what he thinks he has that can help you.

[ukkid35]

Thom said:

Aren't cam caps line-bored with the heads and each marked for their specific position?

On a different engine I replaced a missing cap by removing all the valves and trying a series of spare caps, checking that the cam continued to spin freely when the test cap was torqued up

Engine now has an extra 80k on it so confident that this worked

I now have a spare AJP8 head which was supplied with two damaged caps (from a different head), so I'll end up having to do the same again one day, but with far fewer spare caps

[Thom]

Such breakage can occur if the cap was overtightened, leaving not enough room for expanding when warm. The tigthtening torque really should not be much on those. Not sure of the actual bolt size used here but something like M8 should not need more than 20 N.m.

TwinKam said:

You'll probably have to get a cap made oversized, then machined to suit. Probably head off time.

That's what I would do. Have 10 new cam caps machined out of billet aluminium and line-bore them, as there is no reason the broken cam cap was the only one that was overtightened...

Edited by Thom on Tuesday 7th May 12:46

[Chimp871]

The torque setting is 23nm, so not a lot.

I'm just hoping that a previous owner/garage didn't just put it back knowing it was broken. Not saying it is but it is in my mind, especially seeing the cap scoring, in the bearing edges you can see an indentation. Shame they didn't have traditional cam bearings.

Gruffalo - appreciate you asking Jason.

[ukkid35]

Chimp871 said:

I'm just hoping that a previous owner/garage didn't just put it back knowing it was broken. Not saying it is but it is in my mind, especially seeing the cap scoring, in the bearing edges you can see an indentation.

Looking more carefully at the photos, there is a lot of wear indeed, perhaps a third of the surface area is affected

How do the other cam caps compare?

There must have been some oil contamination to cause that, surely?

[ukkid35]

Chimp871 said:

Any ideas why cap #3, the middle one, would go like that. You'd think it would be the least stressed?

Could have happened when the cam was being removed/replaced, as that is when they are unnaturally stressed

I am very cautious because I use a dummy cam cap in position #3 allowing the cam to be removed/replaced without over stressing

Here is where I fit the dummy

https://www.youtube.com/watch?v=eCEOnI3_-xc&t=...

And about five minutes later when the dummy is finally removed

https://www.youtube.com/watch?v=eCEOnI3_-xc&t=...

[Chimp871]

Spoke to Dom at Powers and shared the photo. To be done properly it's heads off time and then we'll see, he's kindly sending down a cap or two in the unlikely event it'll fit in tolerance. To be honest he said it's never worked for him but I may be lucky, long shot time with plastiguage. He was mentioning tig welding the original but imagine after seeing the cap damage it's not worth it. Perhaps the cam seized at some point to cause the crack but I'm guessing.

My problem is removing the engine/head isn't going to happen overnight due to work commitments and it's not driveable at the moment. I'm probably wanting to do an engine rebuild with Dom, so I can trust it. The problem with our cars are you just don't know what previous owners have or haven't done to the car.

I would like to think a new cap could be made and then line bored in but only time will tell.

[Chimp871]

Couple more photos. Camshaft journal linked to #3 and the odd bank caps ( broke cap was even side)

I'm not a metallurgist or anything but casting pits in the caps shows st quality.

Edited by Chimp871 on Tuesday 7th May 21:56

[Thom]

What oil grade have you been running the engine on?

[Jhonno]

Chimp871 said:

Couple more photos. Camshaft journal linked to #3 and the odd bank caps ( broke cap was even side)

I'm not a metallurgist or anything but casting pits in the caps shows st quality.

Edited by Chimp871 on Tuesday 7th May 21:56

Or contamination?

[Chimp871]

Update. Waiting for a cap or two to try on the heads with plastigauge clearance of 2 thou.

My neighbour used to work at Aston Martin as an engineer and got his opinion. He agreed to get a cap made and line bored, probably £600. Will have to remove lowered cut from valve tips or shims, looking at around 5 thou.

Will need a new camshaft which is around £350 too as its badly scored on #3. Luckily the head cam journals are very good.

Or.... Just get the whole lot to Powers and get a rebuild done.

Either way the engine needs pulling first, then I'll decide on next action.

Glad I have a chimaera 450 to play with over the summer. I do feel that rover lump is a more hardy engine, trying to get it ready for castle Coombe by fitting an oil cooler.

[Jhonno]

Chimp871 said:

Glad I have a chimaera 450 to play with over the summer. I do feel that rover lump is a more hardy engine, trying to get it ready for castle Coombe by fitting an oil cooler.

See, you are basing that on the fact yours has been poorly looked after.. RV8s do their cams for fun, but an AJP doesn't unless someone offers some outside interference.

[Chimp871]

True, but camshaft bearing shells does make life easier.

I'm prepared to look behind the curtain so to speak on these cars, but others won't and will just sell at the first sight of a problem or not divulge it to the new owner. I'm sure there's plenty of scored camshafts, housings out there that no one knows about as they either don't understand the difference a couple of thou makes when pumping oil or just see money being spent.

I'll be putting it right.

[Jhonno]

Chimp871 said:

True, but camshaft bearing shells does make life easier.

I'm prepared to look behind the curtain so to speak on these cars, but others won't and will just sell at the first sight of a problem or not divulge it to the new owner. I'm sure there's plenty of scored camshafts, housings out there that no one knows about as they either don't understand the difference a couple of thou makes when pumping oil or just see money being spent.

I'll be putting it right.

True!

Glad to hear it!