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Do I Have a Flat Top or Dome Top Engine?


Anthony

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Hi all

Can anyone tell me which engine I have?

My recently aquired GT6 engine has an engine number pre KE10000 which leads me to believe it's a flat top..... But It's also got a tag on the head gasket which is only fitted to the models with recessed blocks

My guess is i've got an early engine with the incorrect gasket fitted
I'm going to do a full strip down on it soon so all will be revealed then, but I've got some bodywork to sort out first

Can the recessed gaskets be forced onto the early blocks?
And can the early and late heads and blocks be interchanged?

Thanks in advance

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Yes, a tabbed gasket will go onto a non-recessed block.

And may last for years if you are lucky.

Then may give up suddenly.

I acquired a PI engine setup in that manner.

Had clearly lasted years, a few miles of me thrashing it and it failed, leaking pints of oil.

Cheers

Colin

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1903 wrote:
Thanks Colin

Am I right in thinking it's only the later engines which can be 'converted' to 2.5Ltr?


Nope, all mk2 2ltrs can be converted but earlier flat top will need a 2.5 or late 2ltr head (and pushrods).

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Cool thanks

I have the original engine in the car, so wanted to do something fun with the spare

I guess it'll be easier and more cost effective to start with a 2500cc engine rather than buy all the bits to modify a 2000cc unit

Should I look for any particular 2500cc engine as my base, or is there really no difference?

What kind of hp & tq can I expect from a well sorted 2ltr & 2.6/2.7ltr engine?

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Mk1 2.5 engine is best bottom end (crossdrilled crank and lighter flywheel) Engine prefix CR - or CP if you find an early TR5 engine which is effectively the same bar the cam
There are a very few Mk2 crossdrilled cranks knocking about - 1969 early 70 I think but they have a heavier flywheel.
After that they are all pretty similar and if you are rebuilding with a new cam they are all much of a muchness - carb engines need more skimming of the head (about 0.075") and smaller exhaust valves from about 73/74 onwards makes unleaded inserts easy

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Gt6s wrote:
Nope, all mk2 2ltrs can be converted...


I thought the early MkII engines couldn't ie. GT6/Vitesse MkII, later engines the block was commonised. Who said my PI was common   :P

Check if the bore has a cutout at the bottom? This is to allow the conrod clearance, for the extended stroke of the 2.5.


Willing to be proven wrong....  :-/

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Righty-hoe

I've seen an "MM" engine currently for sale
Is this worth going for or not?

Is this the most de-tuned 2.5 engine available?
I'll end up rebuilding it and going all out anyway, just want to know if there are any reasons to avoid it?

Would this engine require any extra work compared to the others which would make it more cost prohibitive?

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lagerzok wrote:
Mk1 2.5 engine is best bottom end (crossdrilled crank and lighter flywheel) Engine prefix CR - or CP if you find an early TR5 engine  


I seem to remember that in their wisdom Triumph re-used an engine numbering sequence, and CR is also late TR6, and thus does not have the benefits of the Mk1 engine.

Could a CP engine also be an Early TR6 as well??

MM was any later 2.5, so could be a 2.5TC or a 2.5S engine, S is more powerful. Easy to use it for any prupose. A TR6 spec engine I had was buuot with an MM

Cheers

Colin

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MM block is fine for building a 2.5. What spec are you building? If injected you would want to skim the head as it's too tall and has a lower compression ratio.

2 Litre MkII 3.3"  (early flat-top pistons)
2 Litre MkII 3.4"  (late, dome pistons)
2.5PI          3.4"
2500S         3.475"

Presumably you will be changing the cam?  :-/

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If you take a spark plug out and shine a torch through the hole you should be able to see whether the piston has a dome on it as it approaches TDC.

Should be possible to convert any block (apart from very early small bearing ones) to 2.5 although some early large bearing 2.0 might need a bit of fettling to clear rods and crank.

Don't the cross drilled cranks have long tails making them unsuitable for small chassis cars?

Nick

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I haven't got an exact spec in mind at the moment as it's still just an idea in it's early stages

I'm more than happy to skim heads, shot peen parts, and install forged rods etc...

Just wanted to make sure the "MM" engine didn't have any extra problems to deal with compared to the other engines

I've recently read that someone had/has an engine producing 220hp at the wheels....sounds like fun to me

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1903 wrote:

I've recently read that someone had/has an engine producing 220hp at the wheels....sounds like fun to me


Consider claims like that with caution.  Not impossible but involves very serious expense!  Anything over 170 for the 2.5 is good going.

Nick

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Nick_Jones wrote:


Consider claims like that with caution.  Not impossible but involves very serious expense!  Anything over 170 for the 2.5 is good going.

Nick



Thanks for the heads-up Nick
It confirms what most people are saying
I assume that's ~170 at the crank and not the wheels?

I plan on doing quite a bit of work to the engine once I get round to it
Still having to remind myself that there's only a limited amount of power you can get from these naturally aspirated engines

My other car came with 450hp from the factory and with a bit of work 800hp at the rear wheels isn't too difficult

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lagerzok wrote:
There are a very few Mk2 crossdrilled cranks knocking about - 1969 early 70 I think but they have a heavier flywheel.


So MG850 was crossdrilled? that would be the "rare" crossdrilled crank with the short back and Mk2 saloon flywheel - I don't know when they stopped doing them - they are a Mk2 Pi early TR6 item although apparently really early TR6 have a TR5 crank

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My 2.65 makes about 170bhp and 190lbft torque - I have plans to up that to about 190bhp but to be honest if I was doing a GT6 Engine I would stick to a bored 2000 and let it rev hard 7000-7500 is pretty easily attained in a 2000 engines whereas a 2.5 just isn't as capable of those revs and reliability - the basic bore / stroke ratio is just wrong  2100 = 77 x 76mm , 2.65 = 77 x 95mm



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thescrapman wrote:


I seem to remember that in their wisdom Triumph re-used an engine numbering sequence, and CR is also late TR6, and thus does not have the benefits of the Mk1 engine.




Correct Colin......in fact I currently have one in my garage.

Alex

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lagerzok wrote:


So MG850 was crossdrilled? that would be the "rare" crossdrilled crank with the short back and Mk2 saloon flywheel - I don't know when they stopped doing them - they are a Mk2 Pi early TR6 item although apparently really early TR6 have a TR5 crank


I've got MG11, but sadly it lost it's crank before I got my hands on it :-(

It's interesting though as it's a Mk1 block - without the strengther brace in the casting under the manifold!

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MikeyB wrote:


I've got MG11, but sadly it lost it's crank before I got my hands on it :-(

It's interesting though as it's a Mk1 block - without the strengther brace in the casting under the manifold!


A mate of mine has MG75 which spent a lot of its life on a stand in a college it also had the crossdrilled short tail crank.
The strengthener brace you mentioned only appears with the introduction of the recessed bores.

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