Triumph 6 cylinder engine '67 through '76

[arizonamike]

Were there any evolutionary changes or upgrades to the engine over the years or are they all the same?

Thanks

Mike

 

[swift6]

Aside from the major difference of 2.0 litre and 2.5 litre there were some evolutionary differences in each of the engine sizes. The biggest changes were in the heads. Changes in port spacing primarily on the intake side.

With the 2.5 litres the block slightly changed, mostly increasing the stiffness, not really haringin any compatability issues. The crankshafts changed, around 1970. These crankshafts need a matching flywheel but are otherwise interchangable from early block to late block. The early cylinder heads had a narrow intake port spacing until 1972. Intake manifolds are not really interchangeable early to late (they will bolt on but their flow will be interrupted) but exhasut manifolds are. Camshafts changed in later years and those changes often accompanied compression ratio changes. Heads, as a unit, are interchangeable form new to old/old to new just be sure to use the appropriate head gaskets.

Its really a very wide question. If you had something specific in mind you would get more specific answers.

 

[arizonamike]

Thanks Shawn. I was not aware of the 2.0L Vitesse engine until now.

I was just wandering about any 2.5L changes. You answered my question. So, as a general rule. except for heads, replacement parts from the same year engine would be the best way to go ?

Was each flywheel balanced to each crank ?

Would a 1976 TR6 head be higher compression than my 1968 ?

I have not worked on a 2.5L except for maintenance.

Hey I need a set of metric wrenches now.

 

[poolboy]

Not metric...
CR dropped to 7.75:1 from 73 on, but just about everyone who had the head reconditioned in the last 35, 40 years must have had the head skimmed at least a tad.

 

[booley]

Here's a question, I'm toying with the idea of stuffing a TR6 motor in my GT6. I am somewhat familiar with the oilpan modifications needed with a bfh. What year TR6 cylinder head would match my GT6 head?(I have a set of webers I would like to re-use)

 

[dklawson]

The early GT6 heads have pushrod tubes that are aluminum tubing pressed through the head casting. If you have that type of head, you will not be able to use the TR6 heads. If your GT6 head does not have separate pushrod tubes then you can use the TR6 head but you will want/need to modify it.

To keep the compression ratio where they wanted it BL used the same casting in "thick" form for the TR6 and machined it thinner for the GT6. If you put a thick TR6 head on your GT6 short block you will have very low compression.

 

[DNK]

The later heads are the same,...are they not.
Pretty sure my head is a GT6 head from Ted


Oh, the GT head is taller ,I do believe

 

[dklawson]

The later GT6 head is the same as the TR6 head but it is shorter, not taller. It is the same casting as the TR6 but shaved down in thickness to obtain decent compression.

 

[DNK]

Are you sure,Because my new GT6 head is taller than my stock TR6 head

 

[jsfbond]

Thanks Shawn. I was not aware of the 2.0L Vitesse engine until now.

I was just wandering about any 2.5L changes. You answered my question. So, as a general rule. except for heads, replacement parts from the same year engine would be the best way to go ?

Was each flywheel balanced to each crank ?

Would a 1976 TR6 head be higher compression than my 1968 ?

I have not worked on a 2.5L except for maintenance.

Hey I need a set of metric wrenches now.

I was under the impression that the GT6 engine was a de-stroked version of the 2.5 block, resulting in the 2.0 for higher revs. designed for more bullit proof racing.

 

[dklawson]

The GT6 engine was used first in the Vitesse and that in turn was derived from the 1600cc Vanguard engine. The TR6 engine was derived from the GT6.

Yes, the later GT6 engines that use the same head as the TR6 have shorter/thinner heads than the TR6. I'm not sure why your car's is not. Perhaps a previous owner fit a GT6 head and pushrods to really raise the compression ratio a huge amount.

I'm sure there is more info online about this. A quick Google search this morning found the link below:
https://www.oocities.org/rotoflex/gt6-mod.htm

Quoted from that page...
<span style="color: #FF0000"><span style="font-style: italic">Chris Witor researched several Triumph 6 cylinder heads to gauge their flow characteristics. His conclusion was that the 219016 head flowed best. As the 219016 head was originally fitted to the 2.5 engine, it will require skimming if installed on a 2.0 engine to achieve a reasonable compression ratio. </span></span>

 

[Andrew Mace]

The GT6 engine was used first in the Vitesse and that in turn was derived from the 1600cc Vanguard engine. The TR6 engine was derived from the GT6.

Right! The six was derived, in fact, from the four-cylinder that started out in 803cc, then 948, 1147 and 1296. All those, and all the sixes except for the 2.5, had the same 76mm stroke. That 2.5L six was stroked rather more (95mm) than was the 1493cc Spitfire (etc.) "1500" engine (87.5mm).

 

[DNK]

...Yes, the later GT6 engines that use the same head as the TR6 have shorter/thinner heads than the TR6. I'm not sure why your car's is not. Perhaps a previous owner fit a GT6 head and pushrods to really raise the compression ratio a huge amount.

...

Got it straight from Ted.
Now you got me curious and I'm going to recheck just to make sure I'm not talking out my ...SSS.
And my fuzzy memory isn't fuzzier


<span style="font-style: italic">OK, I got my head from Ted, was told it was a GT6 head.
After measuring the volume of one of my cylinders and sending that info to him.
He cut the new head to give it a 9.5:1 ratio.
I just measured the GT6 head and it is 3.58".
Went to my storage loft to measure the stock 71 head.3.53"
Both measured at the spark plug side
</span>

 

[dklawson]

I'm not quite following you Don. Are you saying that you have a GT6 head that measures 3.58" thick?

Check out the web page linked below regarding engine spec comparisons. 2/3 down the page you'll reach the section dealing with cylinder heads:
https://www.triumphclub.co.nz/?page_id=653

The only thing I saw with a head thickness over 3.5" was for a TR-250 (and an African? TR6). Most the GT6 heads are around 3.3 to 3.4 depending on the compression ratio. The 2.5Ls all seem to start at 3.48.

 

[DNK]

Well, where is the correct place to measure.

Though I measured both heads at the same location ,close anyway and the so called GT6 head is taller even after it has been cut.

Maybe it isn't a GT6 head. Maybe he changed his plan on what head to use

Doug, didn't see my 71 head listed ,307837

 

[DNK]

Here is my new head info

And I think it is a Diamond "D" but hard to read inside the diamond

 

[DNK]

Better chart
Head Chart
Looks like it is a TR6

 

[arizonamike]

Thanks fellas, very interesting. The way that they were able to successfully continue to modify their current designs making them larger, rather than starting from scratch with a totally new engine design, seems to have worked up until about 1970, when Triumph tried to weld two of their four cylinder engines together for the new STAG.

The Triumph Club NZ has great information. Thanks for that. Found this video there regarding the above.

Hope it does not offend any Stag owners.

https://www.youtube.com/watch?feature=player_embedded&v=TGJty_Rdp1U#!

 

[jsfbond]

Thanks fellas, very interesting. The way that they were able to successfully continue to modify their current designs making them larger, rather than starting from scratch with a totally new engine design, seems to have worked up until about 1970, when Triumph tried to weld two of their four cylinder engines together for the new STAG.

The Triumph Club NZ has great information. Thanks for that. Found this video there regarding the above.

Hope it does not offend any Stag owners.

https://www.triumphclub.co.nz/?page_id=88

Even more interesting was that quite literally at the other end of the building, Rover had the aluminum block v8, and would not share. Therby killing any chance the stag might have had.

 

[tdskip]

Even more interesting was that quite literally at the other end of the building, Rover had the aluminum block v8, and would not share. Therby killing any chance the stag might have had.

Really? The story as I heard it was that Triumph wanted to go their own way on the Stag engine. Good engine actually, just underdeveloped at time of release and needed more attention than owners were willing to give.

Our Stag contingency will be along shortly to weight in...