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Fitting camshaft bearings - one for the Spitfire gurus!


JohnD
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I want camshaft bearings for my new 2.5L engine, so I turn to the Spitfire experts, although advice from anyone gratefully received.

I've had this done before and the machinist did a good job, but he's snowed under right now and has referred me to a colleague in the next town.      The new guy comes well recommended but has a different attitude so where the old one just got on with it, this one asks me, how tight do I want the cam bearings fitted?   Interference fit, I said.    Ah, but how tight, he replied, 1 or 2 thou undersize?

Early Spitfires were fitted from the factory with cam bearings, and it's those that will be fitted, as production six cylinders had the cam running in the block, as later Spits did.        So can anyone tell me?     How tight should the cam shaft bore be?

Thanks!

JOhn

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7 hours ago, Pete Lewis said:

maybe use a bearing fit loctite to make sure the bush wont rotate 

Nooooo! I had a machinist who thought that would be an ok approach and two of the bearings came out while I was fitting the cam.

I can tell you that on the 4 cylinder 1300 & 1500 engines, all camways are bored to the same size so you can fit shells or not to suit your cam. Only the Spit Mk3 and 1300TC FWD had them from the factory though.

Nick

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2 hours ago, Nick Jones said:

Nooooo! I had a machinist who thought that would be an ok approach and two of the bearings came out while I was fitting the cam.

I can tell you that on the 4 cylinder 1300 & 1500 engines, all camways are bored to the same size so you can fit shells or not to suit your cam. Only the Spit Mk3 and 1300TC FWD had them from the factory though.

Nick

and the spitfire mk2 at least the later ones and I believe the early mk4

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Hello All

               I fitted bearings to the new engine and as far as I know they are still ok (1500)

But I did turn up a Go and No Go gauge to check the bores to make sure they would be ok!

But 5k to 8k later they are still ok.

But John you need a GOOD machine shop to bore them in line and to size 

Roger

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3 hours ago, Nick Jones said:

May well be right about Spit Mk2, but I think the early MkIV thing is a myth.

Nick

Nick, the early MKIV has camshaft bearings as its camshaft is the same one as fitted to the MkIII engine.

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Ok. So is this actually an FD small-crank on the first few hundred, using up stocks, or something more widespread? Or is it a big crank FH with the Mk3 cam. I’ve never seen one (not surprising) and I don’t know anyone who has.

As it happens, our earlyish MkIV does have a full FD engine. But only because we created it specially. The car came with a large crank FH. Didn’t measure the cam but it had no cam bearings.

Nick

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I've found these specs in the GT6 Mk 1 WSM: 

Camshaft

New Dimension Inches

Clearances Inches

Journal Diameter

1.8402

0.0026

 

1.8407

0.0046

Bore in block

1.8433

 

 

1.8448

 

Please ignore the heavy table lines - I didn't put them in!

But what do these specs mean?   Why two dimensions for the journal and bore widths?  Were these the tolerance Triumph worked to?

A journal width 1.8402 in a bore 1.8433 has a clearance of 31 thou.      A journal 1.8407 in a bore 1.8448 has a clearance of 41 thou!    Neither agrees with the stated clearances!

Confusing!

This doesn't answer the machinist's Q, what dimension to bore out to for bearings, but could inform the decison, if I had some illumination!

John

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2 hours ago, Nick Jones said:

Ok. So is this actually an FD small-crank on the first few hundred, using up stocks, or something more widespread? Or is it a big crank FH with the Mk3 cam. I’ve never seen one (not surprising) and I don’t know anyone who has.

As it happens, our earlyish MkIV does have a full FD engine. But only because we created it specially. The car came with a large crank FH. Didn’t measure the cam but it had no cam bearings.

Nick

Nick,

The early MKIV Spit engine (pre FH25000HE) has a large journal crank, but is fitted with the MK3 Spitfire Camshaft.

I've got FH4HE in my stock of core engines, and FH6xxHE in my very early MKIV Spit.

The engine is perkier than the later MKIV Spit engine, but not as high revving as the MK3 engine.

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2 hours ago, JohnD said:

I've found these specs in the GT6 Mk 1 WSM: 

Camshaft

New Dimension Inches

Clearances Inches

Journal Diameter

1.8402

0.0026

 

1.8407

0.0046

Bore in block

1.8433

 

 

1.8448

 

Please ignore the heavy table lines - I didn't put them in!

But what do these specs mean?   Why two dimensions for the journal and bore widths?  Were these the tolerance Triumph worked to?

A journal width 1.8402 in a bore 1.8433 has a clearance of 31 thou.      A journal 1.8407 in a bore 1.8448 has a clearance of 41 thou!    Neither agrees with the stated clearances!

Confusing!

This doesn't answer the machinist's Q, what dimension to bore out to for bearings, but could inform the decison, if I had some illumination!

John

Hello John 

                 I think you will find it is 3.1 Thou and 4.1 Thou

Roger

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5 hours ago, KevinR said:

Nick,

The early MKIV Spit engine (pre FH25000HE) has a large journal crank, but is fitted with the MK3 Spitfire Camshaft.

I've got FH4HE in my stock of core engines, and FH6xxHE in my very early MKIV Spit.

The engine is perkier than the later MKIV Spit engine, but not as high revving as the MK3 engine.

Is it a Mk3 bearing type camshaft, or a Mk3 grind on a non-bearing sized blank.

And I think you have FH14HE. But I only used it and it was sha**ed. Never looked inside.

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1 hour ago, thescrapman said:

Is it a Mk3 bearing type camshaft, or a Mk3 grind on a non-bearing sized blank.

And I think you have FH14HE. But I only used it and it was sha**ed. Never looked inside.

Colin, it’s the MK3 camshaft with bearings in the block.  Same camshaft part number as the MK3 engine

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Hello John

                   They are the same bearings just 2 less so the same! they only left them out to save money!

Basically you have got to have the block bored to the same(Triumph saving money!)

We love our cars but they were parts bin made sometimes!

Just look how many parts fit so many different models?

If you you look at large journal and small journal cams it is the shell difference in diameter!(cheap!!) and more than adequate for a road car!#

Roger 

 

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1 hour ago, thescrapman said:

I thought the bearings push fit into the block, and the journals on the cam are reduced in diameter to suit.

So you just get the 6-cyl cam made with reduced journals.

 

My thoughts too

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