cam bore machining

[PriamEngineering]

Cam bore machining.
I have been working on a OHC small diesel engine. The client has stated that the cam bore has to be machined in its free state. That is no high loaded clamps, or assembly to the block to simulate head distortion during assembly will be allowed during machining. Obviously if I can do this it will be better for the head cycle time. This is an integral bored cam (no cam caps). Does anyone know if this is normal practice?

http://www.priamengineering.co.uk

 

[MikeHalloran]

Diesels with OHC are unusual.
Diesels with nonreplaceable parts, e.g. integral cam bearings, are unusual.

It's what the client wants. THAT's normal practice.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tmoose]

I sure want my cam bearings to be reasonably concentric when the engine is assembled with the head clamped against the (flat) block. That ( cam bore non-concentricity ) is the big argument AGAINST machining a severely warped OHC head's gasket surface without straightening the head first. If the bowed gasket surface is simply machined flat, The cam line will be "frozen" in the bowed state when the head is torqued down. Too much bow, and the cam may suffer.

Makes me wonder if it is instead an unfortunate reference to GD&T standard requirements for inspections to be made with the part in the free state.

A fixture that picks up the head at a few strategic points could provide neutral support for a head, even one with slight but acceptable bow or twist for cam bore finishing

 

[catserveng]

CAT had OHC's in the D343, D346, D348, D349 and D336. In the D336 they published a good set of inspection and rework procedures when it was considered a "high output" engine. CAT spent a lot of time and money on the issue, if you can find someone who still has that older info you may find it helpful.

Mike L.

 

[ivymike]

There was also the C15...

 

[dicer]

In a perfect world of no distortion your customer would be correct. He's living in the wrong world. If the casting is aged and the deck surface is flat on both head and block then it should work as he wants. No matter what make sure he knows that if he specifys how to do the job, then he knows you are not responsible for say a broken cam shaft.

 

[CJ0717]

I've been working with engine blocks and head machining for many years. Never have I experienced the assembly of a head to a block in order to line bore the cam bores. Also it's not too unusual to have a parent metal cam journal (bearingless). Very common in aluminum OHC engines.

If your getting the cam journals line bored. Make sure the head deck is machined prior so that it is completely flat. Within 0.018mm overall. As long as that is flat and the line boring clamp fixture does not distort the head you should be fine. Keep the concentricity /alignment of the inner bores to the outer bores tight. no more than 0.050mm.

 

[patprimmer]

If the gasket face of the head is machined flat, then the cam bores are machined, the head must be held in place to perform the work on the cam bearing bores. I would presume it was bolted to a flat machine bed.

Regards
Pat
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