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Richard71

Saloon Engine Block

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Hello All,

 

An engine block with serial number prefix "MG" has came into my hands, I believe this to be from a saloon 2.5Pi.

My question is, are there any differences advantageous or otherwise between these blocks and TR5/6 blocks.

 

Regards,

Richard.

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Hi Richard,

 

I think you will find that the MG block is the factory Mk2 2.5PI block, so has the recessed bores and extra strengthing rib on the block, so not the same as earlier CP (pre CP75001) but is interchangeable, it would be the same as CR. Triumph thought there was an advantage in doing this but in reality who knows. I have an MG block fitted which appears to be an exchange block, so dealers were swapping them out back in the day.

 

Regards,

 

John

Edited by lightningburns

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Hi Richard,

 

I think you will find that the MG block is the factory Mk2 2.5PI block, so has the recessed bores and extra strengthing rib on the block, so not the same as earlier CP (pre CP75001) but is interchangeable, it would be the same as CR. Triumph thought there was an advantage in doing this but in reality who knows. I have an MG block fitted which appears to be an exchange block, so dealers were swapping them out back in the day.

 

Regards,

 

John

The CR block is more ridged in use, there were problems with the early 2,5 blocks with twisting / warping and valve seat distortion in the cylinder heads hence the change of head gasket and casting design. In my view a better block. This was done to cut down the number of warranty claims due to loss of compression.

 

Bruce.

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I concur that the later blocks have the rib down the length of the block, (exhaust/PI/Carb side), which provides additional strength, and interchangeable, as per above.

 

 

Cheers.

Edited by TRTOM2498PI

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Thanks to all for the info.

 

Is this strengthening rib internal or external? I cant look at the block at the moment, dropped it in at the machine shop.

 

Richard.

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I disagree with some of the above. Definitely not recessed, can't say about strengthening rib.

I built an 'MG' series block up using all the components from a 'CP' engine that had ice damage, with no issues. It certainly appeared identical to me.

Jerry

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The recessed blocks on the 2.5PI were from MG50001 onwards i.e. at the same time as they were introduced on the TR6 at CC75001 / CP75001

 

cheers

 

Derek

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The recessed blocks on the 2.5PI were from MG50001 onwards i.e. at the same time as they were introduced on the TR6 at CC75001 / CP75001

 

cheers

 

Derek

 

The block I have is definitely recessed, though I never took note of the serial number.

 

Richard.

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The block I have is definitely recessed, though I never took note of the serial number.

 

Richard.

Make sure you use the later head gasket for the recessed block, it was designed to give better sealing between the bores!

 

Bruce

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My TR6 is CC78553… on the pic below you can just about see the strengthening rib on the block.

 

My 2000 saloon has an MM code engine from a 2500TC and that also has the rib.

 

Matt

 

DSC0526.jpg

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Thanks Matt, I can see the rib clearly now.

 

On another note concerning the later, improved engine blocks.....if the block was skimmed to accommodate zero piston-deck clearance, would it be safe to assume the recess would have to be re-cut accordingly, does anyone know what the standard depth of the recess should be?

 

Richard.

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Thanks Matt, I can see the rib clearly now.

 

On another note concerning the later, improved engine blocks.....if the block was skimmed to accommodate zero piston-deck clearance, would it be safe to assume the recess would have to be re-cut accordingly, does anyone know what the standard depth of the recess should be?

 

Richard.

 

Richard,

 

I don't know what the standard depth of the recess is, but yes, my block was decked and then had the recesses re-cut.

 

Matt

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I forget the actual numbers now (though there is a thread somewhere on one of the Triumph forums) but it is usually possible to have a very light block skim without needing to re-cut the recesses. I managed this when I built my PI engine. That was an MG prefix block from 1972 with the rib along the bottom of the manifold side.

 

Conversely, if you are decking for a specific purpose (to zero deck your pistons for example) then you will certainly have to either re-cut the recesses or deck far enough to completely remove the recesses for a flat gasket and skim the pistons a few thou as well. I did the latter when I built my Vitesse engine with a late block because I wanted 0.005" pop-up and don't much like the recessed gaskets. Still had to skim the pistons a little, which at least meant they all had identical deck height.

 

Nick

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I forget the actual numbers now (though there is a thread somewhere on one of the Triumph forums) but it is usually possible to have a very light block skim without needing to re-cut the recesses. I managed this when I built my PI engine. That was an MG prefix block from 1972 with the rib along the bottom of the manifold side.

 

Conversely, if you are decking for a specific purpose (to zero deck your pistons for example) then you will certainly have to either re-cut the recesses or deck far enough to completely remove the recesses for a flat gasket and skim the pistons a few thou as well. I did the latter when I built my Vitesse engine with a late block because I wanted 0.005" pop-up and don't much like the recessed gaskets. Still had to skim the pistons a little, which at least meant they all had identical deck height.

 

Nick

Hi Nick, the recessed block head gasket had a fire ring design based upon formula 1 design for their application and gave much better sealing than the original design of head gasket which often blow between bores because of a lack of rigidity of the block!

 

Bruce.

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Hi Nick, the recessed block head gasket had a fire ring design based upon formula 1 design for their application and gave much better sealing than the original design of head gasket which often blow between bores because of a lack of rigidity of the block!

 

Bruce.

 

No doubt that is the intention. In fact I've never had any problem with the flat gasket on the Mk2 version of the 6 cylinder engine (in spite of working them quite hard). The Mk1 version and the 4 cylinder engines are a different story but they only have weedy 3/8" studs and don't get clamped down properly.

 

Nick

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