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john.r.davies

Bore size for cam shaft bearings

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I have a TR6 engine whose camshaft ate the block.

It was in a car I bought, newly-rebuilt engine, no history, but subsequent post mortem found that the cam was high lift, the roller rockers were higher than normal ratio, and the valve springs were far too stiff. Baaaaaaaad mistake.

 

If the cam bore is not too damaged, I'd have it bored for bearings and rebuild it.

But what is the required diameter of the bore for bearings?

 

I'm certain somebody can tell me.

Please do?

Otherwise another six block goes to the scrapper.

JOhn

Edited by john.r.davies

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John,

if the block proves to be a scrapper I have a couple of spares, you're welcom to one. Just dont ask me to post it!

Peter

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I have a TR6 engine whose camshaft ate the block.

It was in a car I bought, newly-rebuilt engine, no history, but subsequent post mortem found that the cam was high lift, the roller rockers were higher than normal ratio, and the valve springs were far too stiff. Baaaaaaaad mistake.

 

If the cam bore is not too damaged, I'd have it bored for bearings and rebuild it.

But what is the required diameter of the bore for bearings?

 

I'm certain somebody can tell me.

Please do?

Otherwise another six block goes to the scrapper.

JOhn

 

I had the block line bored for the spit cam bearings when I did my TR6 engine a few years ago. I just gave the machine shop the bearings and he bored to suit.

 

Just did a quick search of the 6-pack archived and found this from 2008:

Here is what TRF sent me when I did mine:Use cam bearings for a 1296 cc spitfire engine.  You use the small journal bearings (width).  The wide bearings go in the outside bearings and the narrow bearings go in the center.  The bores must be bored to 1.9680 - 1.9695 to fit the bearings.

Cost me about $20 for the bearings, $600 for the line boring..

 

Stan

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John,

 

I have a (second) block in for this treatment at present. Figures I have are:

 

Nominal 50mm with 49.98 - 50.025mm tolerance range (or 1.9680 - 1.9695" as above!)

 

Make sure that who ever you get to do it has machinery/tooling to allow it to be done from one end in one go. Trying to do it from two ends will not go well - I have this T shirt and scrap block to prove it...... :( Needless to say my second block is with someone different!

 

The cam bearing set you need is 142647K

 

Cheers

 

Nick

Edited by Nick Jones

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Thanks, Nick and Stan - great that you both agree!

 

And thank you, Peter!

Everyone, the reason why I'm thinking another engine build is that I blew the head gasket at Anglesey, yesterday, three laps into practice.

Peter helped me change the gasket in four hours, so that I was back on track for the last race.

And blew the gasket again, all the water into the sump, probably hydraulicked a piston or two and blew some big ends.

And he's offering me a new block as well!

Take a bow, Peter! And thank you!

 

John

 

PS And according to my telescopic bore gauge and micrometer, the widest diameter is 1.925ins! So it is salvageable!

But PM first on the engine that disgraced itself at Anglesey.

That I had fitted with cam bearings, on general principles! Some engines just aren't grateful. J.

Edited by john.r.davies

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Thanks, Nick and Stan - great that you both agree!

 

And thank you, Peter!

Everyone, the reason why I'm thinking another engine build is that I blew the head gasket at Anglesey, yesterday, three laps into practice.

Peter helped me change the gasket in four hours, so that I was back on track for the last race.

And blew the gasket again, all the water into the sump, probably hydraulicked a piston or two and blew some big ends.

And he's offering me a new block as well!

Take a bow, Peter! And thank you!

 

John

 

PS And according to my telescopic bore gauge and micrometer, the widest diameter is 1.925ins! So it is salvageable!

But PM first on the engine that disgraced itself at Anglesey.

That I had fitted with cam bearings, on general principles! Some engines just aren't grateful. J.

John

Well thankyou, It was most enjoyable - in the sunshine, the sea breeze, sounds of racing engines. And the excellent acess to the engine both sides is a big improvement over the 6

 

Puzzling that it let go twice after a couple of laps.Could it be the coolant being dumped by gas pressure in the water jacket from a porous block - followed by gasket failure as it overheats? Dont know how to check for a pinhole in a bore - compressed air down the plug hole I guess, and listen for a hiss??

Peter

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John,

 

I have a (second) block in for this treatment at present. Figures I have are:

 

Nominal 50mm with 49.98 - 50.025mm tolerance range (or 1.9680 - 1.9695" as above!)

 

Make sure that who ever you get to do it has machinery/tooling to allow it to be done from one end in one go. Trying to do it from two ends will not go well - I have this T shirt and scrap block to prove it...... :( Needless to say my second block is with someone different!

 

The cam bearing set you need is 142647K

 

Cheers

 

Nick

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I know this is an old thread but can anyone recommend a company that can line bore a triumph 6 block to take spitfire cam bearings. I have tried a few companies in bucks and oxfordshire but none seem able to do this.

Thanks

Chris

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Mine was done by Lancaster Engines: https://www.lancasterengines.co.uk/

A bit out of your way though.

 

I didn't complete the above story. The block 'eaten' by the cam shaft was scrap. Although the wear at the front would have allowed rebowing for bearings, the shaft must have bowed, as in the middle it was excessive, far too much. But I rebuilt another block, with cam bearings, and also scrapped the experimental head that blew head gaskets.

 

John

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John,

 

I have a (second) block in for this treatment at present. Figures I have are:

 

Nominal 50mm with 49.98 - 50.025mm tolerance range (or 1.9680 - 1.9695" as above!)

 

Make sure that who ever you get to do it has machinery/tooling to allow it to be done from one end in one go. Trying to do it from two ends will not go well - I have this T shirt and scrap block to prove it...... :( Needless to say my second block is with someone different!

 

The cam bearing set you need is 142647K

 

Cheers

 

Nick

As Nick has quite rightly pointed out this is a specialist job. There are not many people that can do line boring make sure you go to someone who has a good track record. It is a precision job and working to very tight tolerances! Expect to pay £200+ for a proper job.

 

Bruce.

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I had my engine block machined at Ivor Searle in Soham, including line boring for cam bearings. Highly recommended.

Edited by matt george

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I had my engine block machined at Ivor Searle in Soham, including line boring for cam bearings. Highly recommended.

+1 for Ivor Searle. He would be one of the people that I would recommend!

 

Bruce

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I have a TR6 engine whose camshaft ate the block.

It was in a car I bought, newly-rebuilt engine, no history, but subsequent post mortem found that the cam was high lift, the roller rockers were higher than normal ratio, and the valve springs were far too stiff. Baaaaaaaad mistake.

 

If the cam bore is not too damaged, I'd have it bored for bearings and rebuild it.

But what is the required diameter of the bore for bearings?

 

I'm certain somebody can tell me.

Please do?

Otherwise another six block goes to the scrapper.

JOhn

 

John ,

 

Even if the camshaft bores in the block are outside the diameter of the camshaft bearings, this can be retrieved by the use of new bushes made from Marine Bronze. So don't think it is necessarily a bin job? They will probably last longer than shells.

 

Bruce

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I know this is an old thread but can anyone recommend a company that can line bore a triumph 6 block to take spitfire cam bearings. I have tried a few companies in bucks and oxfordshire but none seem able to do this.

Thanks

Chris

Chris,

Go to Serdi in Uxbridge they do line boring but usually have a long lead time as they do white metalling as well.

 

Bruce.

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Thanks for the replies. My current block has worn cam bores so drops oil pressure when hot but has relatively new +40 pistons. I have a 2000 engine which is all standard but I would need to buy a bew set of pistons and maybe rebore so just looking for the best option. I will speak to Ivor Searle or Serdi

Chris

Edited by TRsixchris

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just had mine done.. Talk to Jason at TRGB, he has a machine shop nearby who does it.

Tim

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just had mine done.. Talk to Jason at TRGB, he has a machine shop nearby who does it.

Tim

 

Jason gets all the TRGB stuff done at Ivor Searle. I've been working with him on my TR's engine rebuild and learning plenty along the way :)

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Chris,

Go to Serdi in Uxbridge they do line boring but usually have a long lead time as they do white metalling as well.

 

Bruce.

Chris. From my own experience I re-built my engine 18 months ago I was told by the M/C Shop in Slough that Triumph engines are poorly balanced and was talked into having this done as well as re-boring etc. All I can say is that as soon as I drove the car up my road on an unrun in engine I certainly noticed the difference! My engine is now run in and runs very smoothly, it was never like that before.

 

Bruce.

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Mine was done by Lancaster Engines: https://www.lancasterengines.co.uk/

A bit out of your way though.

 

I didn't complete the above story. The block 'eaten' by the cam shaft was scrap. Although the wear at the front would have allowed rebowing for bearings, the shaft must have bowed, as in the middle it was excessive, far too much. But I rebuilt another block, with cam bearings, and also scrapped the experimental head that blew head gaskets.

 

John

 

John,

 

I suspect that your middle bearing could have been saved by re-bushing as already described.

 

Bruce.

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Too late now, but thanks for the suggestion (rebushing). Is that just a bigger bore with a bronze bush pressed in and the bored to the correct size to take bearing shells?

Triumphs being badly balanced? Any six cylinder (or twelve) is inherently balanced better than any other engine configuration, inc. v6s. A full crank pulley, flywheel and clutch cover balance can help if high revs are planned, if you noticed a difference inroad use good for you!

 

John

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Too late now, but thanks for the suggestion (rebushing). Is that just a bigger bore with a bronze bush pressed in and the bored to the correct size to take bearing shells?

Triumphs being badly balanced? Any six cylinder (or twelve) is inherently balanced better than any other engine configuration, inc. v6s. A full crank pulley, flywheel and clutch cover balance can help if high revs are planned, if you noticed a difference inroad use good for you!

 

John

John,

 

Once the bronze bush is pressed into the oversize cam bearing bore, it is then line bored back to original size with .003" running clearance. The camshaft runs directly on the bronze or it can be bored to accept the shell bearing using a steel bush, instead of bronze. I have seen this done on a number of vintage cyl. blocks This method does evolve some precise machining but you save the block from the bin. With regard to balancing, I was shown the figures and mine was all over the place, This also included balancing by weight.

 

Bruce.

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John,

You are absolutely right, a straight six is inherently balanced. But it still needs the rotating mass balanced to give truly silky smooth operation.

Cheers

Tim

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John,

 

Once the bronze bush is pressed into the oversize cam bearing bore, it is then line bored back to original size with .003" running clearance. The camshaft runs directly on the bronze or it can be bored to accept the shell bearing using a steel bush, instead of bronze. I have seen this done on a number of vintage cyl. blocks This method does envolve some precise machining but you save the block from the bin. With regard to balancing, I was shown the figures and mine was all over the place, This also included balancing by weight.

 

Bruce.

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I know this is an old thread but can anyone recommend a company that can line bore a triumph 6 block to take spitfire cam bearings. I have tried a few companies in bucks and oxfordshire but none seem able to do this.

Thanks

Chris

Rob Walker Engineering Witney

 

Can highly recommend.

 

http://www.robwalkerengineering.co.uk/aboutus.html

 

Alan

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I know this is an old thread but can anyone recommend a company that can line bore a triumph 6 block to take spitfire cam bearings. I have tried a few companies in bucks and oxfordshire but none seem able to do this.

Thanks

Chris

Chris,

They are a long way away from you but Alex Carr in Hull have successfully line bored for cam bearings on several 6 cyl engines for me.

 

Dave McD

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