8 replies to this topic

[Ballas]

My dad purchased a 1275 GTS engine a good few years ago, but I am battling to find solid info on this engine. Let's just remember that they only built just over 4000 of them in South Africa. Apparently the crankshaft was cross drilled, it had 3 compression rings and the inlet valves were larger(35.6mm). The pistons I have, have got two compression rings, the inlet valves are 33mm and the crankshaft is not cross drilled. The only definite item is the block, which is marked 12H-GTS. Does anyone have any solid info on this engine?

[Spider]

I don't have printed info on them, however, as far as performance items go, it's essentially the same spec as the MKIII UK Cooper S Engine in terms of Piston Type, Valve Sizes, Compression Ratio and Cam Profile.

 

Has the Crank go a number forged or stamped in to it?

[Itsaminithing]

https://classicregis...eyland-mini-gts

Check out the 'Engine number' & 'Mechanical features' sections they will give you all the info you require.

 

Also found this

....increasing the bore of the block and shortening the stroke, highly polishing the combustion chamber, cross drilling the crank, and adding aluminum pistons and new steel-alloy valves. After all was said and done, the GTS tested one MPH faster than the Cooper S

[Ballas]

I will have to check, I don't have the crank with me, it's at my dad's house. Will find out.

[Ballas]

Apparently the gts head had an issue regarding the valves. The head used to crack between the inlet and exhaust valves. Not to sure if the CooperS had the same issue. This might explain why the valves are smaller than what they should be, because the original head got busted. How can I find out if my cam is correct?

[Ballas]

And does anyone have info regarding the 3 compression rings. I found a very blurry data sheet on pinterest, that stated 3 compression rings, but no where else can I confirm if it is true of not. I will add this though, that when I bought hastings piston rings there were 8 secondary rings supplied. Thought it was a packaging error, but when I came across that data sheet it got me thinking. By the way thanks for all help guys!

[Spider]

Apparently the gts head had an issue regarding the valves. The head used to crack between the inlet and exhaust valves. Not to sure if the CooperS had the same issue. This might explain why the valves are smaller than what they should be, because the original head got busted. How can I find out if my cam is correct?

 

The MKI and early MKII S's did have a tendency to crack, but these were a different casting (AEG163) and a bigger Exhaust Valve. Late in the MKII and the MKIII era, they went to a different casting (12G940) and dropped the size of the Exhaust Valve. To off-set the smaller Exhaust Valve, the Cam Timing had 10⁰ extra duration on the Exhaust. Cracking with this arrangement was fairly rare. I'm pretty sure the GTS had the 12G940 castings.

 

And does anyone have info regarding the 3 compression rings. I found a very blurry data sheet on pinterest, that stated 3 compression rings, but no where else can I confirm if it is true of not. I will add this though, that when I bought hastings piston rings there were 8 secondary rings supplied. Thought it was a packaging error, but when I came across that data sheet it got me thinking. By the way thanks for all help guys!

 

In order to achieve the 9.75:1 CR that these engines had, the Pistons would have had a 6.6 cc Dish. I'm pretty sure that the Pistons were sourced from the UK (Hepolite / AE) and in which case, by that era, they would have had 2 Compression Rings and 1 Oil Control Ring.

[Ballas]

Ok cool so it was a casting issue. I do have 940 casting, so if I want to put bigger inlet valves do I need to offset any valves?

[Spider]

Ok cool so it was a casting issue. I do have 940 casting, so if I want to put bigger inlet valves do I need to offset any valves?

 

No need to off-set the Valves. In the Cooper S and I'm sure the same with the GTS, it was only the Inlet that was bigger.

 

I routine fit hardened seats in to the Exhausts on these heads for Unleaded fuels, again, without issues.