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John McCormack

DIFFERENCE BETWEEN CP AND CR BLOCKS

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My CP car has a CR block. It has all the CP bits such as the head, metering unit, cam, manifolds.

What if any differences are there between the two blocks. Is the CR a better block?

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If you look at the moss catalogue it tells the differences,   https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/engine/engines-components/external-engine-tr5-6.html

I think the main items are the later CP had a strengthening along the lower part of the block.

And later the top the cylinder bores there is a recess to make a better seal on the gasket.

For a recessed block there is a special cylinder head gasket, and is identified by a tab sticking out at the rear of the gasket.

Others may be able to add some more detail perhaps

John

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5 hours ago, John L said:

If you look at the moss catalogue it tells the differences,   https://www.moss-europe.co.uk/shop-by-model/triumph/tr5-6/engine/engines-components/external-engine-tr5-6.html

I think the main items are the later CP had a strengthening along the lower part of the block.

And later the top the cylinder bores there is a recess to make a better seal on the gasket.

For a recessed block there is a special cylinder head gasket, and is identified by a tab sticking out at the rear of the gasket.

Others may be able to add some more detail perhaps

John

JRT modified the Blocks & Cyl. heads a number of times  during the Production life of this engine so in my view it can be said that the later produced engine is much better than the early versions. Here are some of the reasons why: Block distortion and twisting, cracking between valves and cracking to water jacket in the cyl. head, blown head gaskets. wall thickness in block & cyl. head increased in certain areas, plus webs added. I saw examples of these problems during my apprenticeship in our engine test room.

Bruce.

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1 hour ago, Tom Fremont said:

...but doesn't the later block require the short-back crankshaft ( with its attendant ponderously heavy flywheel )?

 

Tom

Yes you are correct but the question related to the cast iron bits. JRT were doing mods in the early 1970's on CP engines and continued on CR types until  the mid 70's, This was always a surprise. to me as JRT already had their new straight 6 OHC engine developed and badged Triumph on the cam cover , seen with my own eyes! but as Rover needed an engine for the SD1 they sole it, for there use It would be interesting to drive a TR6 with the 2.6 version and it was already Federalised for the US market . The Heavy flywheel was to improve tick over???? When I rebuilt my  CR engine in 2017 I had it lighten!!! and all the reciprocating parts rebalanced. 

Bruce.

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I didn't think tickover needed improvement, but note there is a 300 rpm increase in the redline on the later engines. I reckoned this was due to the heavier flywheel and " holy " rods used on them.

After 43 years of owning TR250s I am reconciled to 150 BHP being what these engines will be capable of without compromising longevity ( which is very good, IMO ). The old blocks are good for that, and due to the Achilles Heel ( camshaft/valve train I contend ) not a hell of a lot more is to be had irrespective of the blocks. That said, I'll be putting Carillo rods and forged pistons in the next rebuild, whenever that is, to vie for 160+ BHP with infinite life :P

 

Tom

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18 hours ago, Tom Fremont said:

I didn't think tickover needed improvement, but note there is a 300 rpm increase in the redline on the later engines. I reckoned this was due to the heavier flywheel and " holy " rods used on them.

After 43 years of owning TR250s I am reconciled to 150 BHP being what these engines will be capable of without compromising longevity ( which is very good, IMO ). The old blocks are good for that, and due to the Achilles Heel ( camshaft/valve train I contend ) not a hell of a lot more is to be had irrespective of the blocks. That said, I'll be putting Carillo rods and forged pistons in the next rebuild, whenever that is, to vie for 160+ BHP with infinite life :P

 

Tom

Hi Tom,

In the BL Triumph Competition Preparation Manual TR250.TR5,TR6, it clearly shows in their power graphs taken from their Dynomometer tests that they were able to obtain 140 to 190+ bhp. This booklet was for the USA Market so you s/b able to obtain 160 with ease? I used this booklet as a guide for my engine rebuild. My car has not yet been dyno. tested as it has done under 5K but definitely has a lot more power judging by the way it now climbs local hills around where I live.

Bruce.

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On 3/14/2019 at 2:10 PM, Tom Fremont said:

...but doesn't the later block require the short-back crankshaft ( with its attendant ponderously heavy flywheel )?

 

Tom

Don't think so - the cranks have to have the correct flywheel but will fit either block.

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The shorter crank will have a higher natural frequency, whether trivially so or not. That may even be a factor in the 5800 rpm redline vs. 5500 for the longer ones. 

Not going to try to compute that one, though!

 

Cheers,

Tom

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