Cam Bearings

[cerbhead]

I notice that the cam bearings are actually machined directly in the alloy of the head - ie no bearing shells. What happens when these 'bearings' wear or get badly ribbed?? Does it mean a new head - which you can't get?? Or is there a fix? Doesn't seem a particularly clever design IMO I see the cam followers are the same.....

[ridds]

The same on all engines these days.

If they do wear out you have a serious problem anyway.

Options are, new heads or bore them out and have a new cam machined with larger journals.

[Julian64]

Yep, I wondered re this and the fact that apart from throwup oil there didn't seem to be a decent lubricating system.

I assume it will be machined head and fitted shells. I would have like to see a bit of phosphor bronze at the very least, but no .

Luckily after 30 thousand miles on my 2000LW my cam and follower surfaces were completely unmarked.

Still it makes you wonder what would happen if one of your cam cap nuts was either done up too hard or too soft

[ridds]

Seen this, cam caps bolts left loose on end cap.

It wobbles, knocks out one side, lifts teh cap off bent, carries on running and wobbles a bit more wearing a funny shape into the cap.

Eventually the last bolt gives way and the end of the cam shaft makes a bid for freedom.

[cossiemetro]

slick 50 seems to be an insurance i've always used it will be putting it in the cerb soon
i know i know its a gimick but i've had some cars a 911 for one that made it seem a little better

[GreenV8S]

cossiemetro said:

slick 50 seems to be an insurance i've always used it will be putting it in the cerb soon
i know i know its a gimick but i've had some cars a 911 for one that made it seem a little better

It isn't insurance, it's just clogging up your oil filter, reducing oil pressure and increasing engine wear. Your Cerbera engine doesn't deserve this sort of abuse.

http://skepdic.com/slick50.html

[cossiemetro]

well i've not put it in yet lol

my frontera seems ok with it in and that a state of the ARK 2.0 8v high performance
precision piece of engineering :laugh:

[Julian64]

Quinny said:

Motorcycle engines have had the cams running directly in the heads for years, and look at the revs some of them get up to

As long as the oil is kept clean and fresh, and there are no problems with supply there's no reason why this type of cam fitment won't go on for many thousands of miles.

If you think about it, the cam and the head should never actually touch each other in normal use

Yep but correct me if I'm wrong but my R1 has hollow cams with an oil feed up the centre that centrifugally spout out oil to the camways.

AS for the cam don't touch the heads I don't understand. the cam caps are the only thing stopping the cams for spinning out into outer space when the lobes push the top of the valves. They take all the reaction force of pushing the valve spring down so they must touch.

[longbow]

Its difficult to appreciate, but an oil film does prevent actual physical contact - it forms a microscopic shear layer which is absolutely critical to the operation of plain metal bearings such as cams/cranks etc. I think this is what he means!!

[Julian64]

I'd be quite happy with an oil film if someone were to tell me how the oil is going to get there

[longbow]

I'm pretty sure there are small oil feed holes in the lower cam cap bearings. But having said that I can't remember for sure. I know when I was looking at the block today the oil feed holes to the heads are very small indeed, probably only 2mm diameter - which I thought was a bit meagre to say the least.

[ridds]

Agree with the slick 50 comment, have even heard of this stuff clogging up VVT unit filters. Very bad and if the feed to Cerb camshafts are that small then this stuff is a defo no no.

[cerbhead]

Hmm..thanx all. I didn't know about bike engines running cams in the head alloy... just looked a bit odd to me. There are a couple of grooves in one of my bearings and while not serious just wondering about if they were. I guess welding and line boring would be one fix....but sounds extreme. A reminder to be very careful not to introduce the smallest piece of crap when setting tappets .

Re oil feed. There is an oil passage up the front of the head casting (the one that needs the 'o' ring in the head gasket) that feeds the front cam journal and sends oil through the cam centre boring to the other journals. Oil leaks out of the cam bearings onto the cam followers and into the valve gallery, and from there falls back down to the sump.