Cross drilled crank

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JohnD
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Cross drilled crank

#1 Post by JohnD » Fri May 21, 2021 1:45 pm

I have found a six cylinder, 2.5L Triumph engine with a cross drilled crank. The block has the number MG 7845HE, which makes it an early 2500 saloon engine.
The big end journals have brass orifices fitted to the ends of the diagonal drillings from the mains, and I am informed that this was the factory fitting, so probably not modifed later.
I have learnt that TR4s were cross drilled and that this was carried over to the TR5, but not the TR6.
T2500s were in production before the TR5. Did early 2500s like this one get cross drilled cranks? Or was the crank transplanted later from a TR5 to a saloon block?

The crank is badly worn but potentially recoverable - is this an 'important' find or not? Should I chuck it, or does it deserve a museum?
John

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Alec
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Re: Cross drilled crank

#2 Post by Alec » Sat May 22, 2021 7:54 am

Hello John,

The early Mk 1 PI engines had cross drilled cranks, I believe? The flywheel is different to the standard flywheel due to a different crank length (refered to as long back and short back cranks) and is also a bit lighter.
You may find that there are people out there who would be happy to buy it from you?
Gary Thomas a well known Triumph performance engine guru, albeit rather contraversial, says in his book that the cross drilled crank is the best basis for building a performance engine. (Other than a specialised after market steel crank)

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

JohnD
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Re: Cross drilled crank

#3 Post by JohnD » Sat May 22, 2021 9:12 am

The archivists over on TRR have found that:

All TR4s were cross drilled, but that's not a crank like this!

All TR5s were cross drilled.

TR6s were cross drilled, up to CP 52329

2500 engines were cross drilled until MG 10323

and they have original Triumph dealer Newsletters to prove it!

So this item is hardly unusual or even rare, and was probably native to that MG block in the first place.

Hey Ho! I thought I had something special!
John

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Alec
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Re: Cross drilled crank

#4 Post by Alec » Sat May 22, 2021 9:26 pm

Hello John,

I think that they are quite rare now, so many of these cars have been scrapped, fewer TRs certainly.

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

JohnD
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Re: Cross drilled crank

#5 Post by JohnD » Sun May 23, 2021 10:12 am

I would let it go to anyone who wanted it, for a suitable charitable donation.
Despite it's credentials, it is too worn for my racing usage.

As we may assume that it's in its original block, transport would change from weighty to massive!
Glad to discuss with any interested person.

JOhn

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Re: Cross drilled crank

#6 Post by bigestate » Fri May 28, 2021 12:11 pm

JohnD wrote:
Sat May 22, 2021 9:12 am
The archivists over on TRR have found that:

All TR4s were cross drilled, but that's not a crank like this!

All TR5s were cross drilled.

TR6s were cross drilled, up to CP 52329

2500 engines were cross drilled until MG 10323

and they have original Triumph dealer Newsletters to prove it!

So this item is hardly unusual or even rare, and was probably native to that MG block in the first place.

Hey Ho! I thought I had something special!
John
Everyone will be checking their MG engines now :mrgreen:

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