Excessive camshaft end float

[lotusfan]

The head is currently off my Sprint engine because of water in the oil. Whilst looking for clues I noticed that the inlet camshaft has far more end float than the exhaust. Inlet camshaft axial movement is approx 3/16 inch and the exhaust is about 0.010 inch. WSM says 0.003 - 0.010 inch.

I had assumed, obviously wrongly, that the chain and the idler sprocket would keep the camshaft in the right place but wear on one side of the idler sprocket says not. Presumably this needs some welding to build up the slot in the head to reduce the end float.

Photo tries to show excessive slot width.

[rgh0]

Clearly a lot of wear in the locating slot in the head for some reason. Never seen this before in even the high mileage heads I have seen, so maybe something wrong with the chain alignment or cams / sprockets / crank that needs to be understood and rectified

Always interesting to see a new failure mode and understand its root cause

Welding up and re-machining the cam thrust locating slot certainly possible if you can find a good welder and good machine shop but it will not be cheap and is getting into the cost point of find a new head or live with the problem. May be easier and cheaper to re-machine the slot and some how fit and secure a spacer.

cheers
Rohan

[oldelanman]

Is the jackshaft sprocket spacer fitted ? No idea if assembly is even possible without it so I may be talking rubbish

[lotusfan]

Rohan

I'm glad you replied, I value your opinion, thank you.

Roger

Thank you, that could be a possibility and I may need to remove the timing cover to confirm. I had thought of that but doing a crude measurement of the gap between case and sprocket showed it is about the same as cam sprocket to inside of head.

Supplementary question now - given that a weld repair to the head is on the cards I have an idea there is someone in the Bristol area who comes highly recommended. I have his name some where but can't find it - help?

[nigelrbfurness]

If you are in the Bristol area then you are thinking of Nick Stagg, out near Iron Acton. He's on here so will probably pop up in a bit.

[vstibbard]

Maybe at some point maybe the spacer on the dizzy drive shaft was not fitted....

[2cams70]

The inlet camshaft is on the same side of the engine as the tensioner bracket. Check the brass tensioner bracket to determine if it is bent (may have happened in the past though and fixed by PO). It's not a problem that caused your coolant leak so if the engine was running OK before it may be OK to just leave as is. The chain and exhaust cam will still restrain things from floating around. Check the worn thrust surface for oil gum and varnish. If it exists you know there is no problem to leave as is because there has been no recent metal contact there and the problem causing it likely happened in the past and was subsequently fixed

[alan.barker]

I think i would look at machining the groove and make a special Thrust Washer
Alan

[lotusfan]

Nigel - Thank you for Nick's contact details, I sent him a couple of pictures and his view was that the head was soft having been overheated at some time in the past and although probably repairable it was likely to always be questionble.

vstibbard - I had thought of that but I think it is there because there is very little clearance between the front of the jackshaft sprocket and the inside of the timing case.

2 cams70 - You may be right about the brass tensioner bracket, the face contacted by the plunger is not in the same plane as the pivot pin so may be partially responsible.

Alan - see first comment to Nigel - new head required!!

Thank you all for your helpful comments.

[alan.barker]

There were some posts in the past about heat treating Heads that are too soft
Alan

[lotusfan]

Alan - thank you, I will do some more research.

[avro]

When Mike sent some pictures to me of his cylinder head the problem he has with the camshaft thrust groove was unfortunately the least of his problems as welding and re machining of the groove is a fairly straight forward operation.
The recession on the head bolt platforms and cracks is of far greater concern. I don’t think l have seen head bolts that have sunk into a head casting quite so far. At some time in its life the engine has suffered some extreme overheating and the casting has become very soft.
I have machined and fitted steel inserts to the platforms on some heads but as l said to Mike l think this particular head has come to the end of its useful life. If you look at the adjacent cam follower sleeve it can be seen to have come loose and turned due to the expansion of the surrounding alloy. The cam lobe has been chipping away at the top of it. Mikes initial problem with water in the oil and the reason for removing the head is most likely due to losing the torque setting on the head bolts because they have sunk into the head so far thus causing the head gasket to fail.

Nick

[Hawksfield]

Mike

I feel for you as that condition is pretty extreme for a lotus head, it must have been making some strange noises prior to pulling it apart

I would be upset to find mine in the same condition, as finding another head in good condition is difficult and not without danger of getting some other persons rubbish.

It would push me start saving for new replacement head considering the price of a sprint today!

Hope the end result is not the extreme it could be

Good luck