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GT6 GT6 Engine Identification Help Needed...

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Flinkly

Jedi Trainee
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ok,

so i finally got my engine back from the shop and have begun looking into what i've got and what i should do with it. i've searched and read through some information regarding the different head castings, but am still confused as to what it all means in my case scenario.

i have the original engine block from my october 1971 GT6 MK3 with rotoflex rear end, but my head is a 218225. it is supposed to be ran with domed pistons, but i am getting ready to install .02 flat topped pistons. i'm sure i'm fine, but what does this mean to me as far as an estimated compression ratio? are there any small things i should do now to improve my engine before i assemble it?

i guess i've just got cold feet and don't want to remember to do something after the fact. or hear about something either.
 
What you need to do is what they call "CC" the head. With a small piece of plexiglass and a spark plug a little clay for sealer you measure the total volumn of the combustion chamber.You should have a 50ml syringe and inject ATF through a hole in the plex till the chamber is full. If you cant figure your comp ratio from there you should not be driving a motor vehicle.....
MD(mad dog)
 
Flinkly said:
i have the original engine block from my october 1971 GT6 MK3 with rotoflex rear end, but my head is a 218225. it is supposed to be ran with domed pistons, but i am getting ready to install .02 flat topped pistons. i'm sure i'm fine, but what does this mean to me as far as an estimated compression ratio? are there any small things i should do now to improve my engine before i assemble it?
Click to expand...

We really need the number of the block to sort it out.

The chronology of the Mk3 engine has to do with the BL solutions for lowering compression for the US market & reducing the number of variations of parts for the 6 cylinder engines in *all* Triumph cars.

There is some info about GT6 blocks & heads at
https://www.britishcarforum.com/tikiwiki/tiki-index.php?page=Triumph+GT-6#_Engine_data_amp_comparison
https://www.britishcarforum.com/tikiwiki/..._amp_comparison

The important point will be learning if your block is KF10001E or later.

For the late Mk3 engine the block was changed at KF10001E. The deck was raised slightly & machined to create a recess around the bores on the deck to accommodate a different head gasket. The head you have is for the late Mk3, & has deep combustion chambers which will interchange with longer-stroke 2.5 litre engines.

Using that head (& with the revised block), to keep the compression ratio high enough for even the low-compression US emission-spec GT6 engines, domed pistons had to be used.

So with that head & a switch to flat pistons, the compression ratio will be reduced unacceptably for performance. I mean down to the floor.

You can have the block decked deeply enough to remove the recess, & shave the head sufficiently to get up to a desired & useful compression ratio. The drawback is that you'll need to CC the head, always remember that the block has been decked so you'll need the earlier non-recessed block's head gasket, plus the expense of a machine shop to do the block & head shaving.

The sticky part is that you've already got the flat pistons. Are they already assembled in the engine?

Still, the block number is neccessary to form a plan.
 
dang...

i'm pretty sure i have a block after 10,000. it's in another state than me right now, and will be for about 2 weeks. i'm sure i can find it in my old posts. it had flat top pistons in it before and it is recessed. i'm gonna have to look into if the head had been previously skimmed down...

i asked the same questions awhile back and everyone said that domed pistons were uneccessary and it already came with flat topped so i just continued the trend. what ratio should i be going for if i want to run regular unleaded? 9:1?
 
my block is KF10255UE and here is my old thread on pistons:

https://www.britishcarforum.com/bcforum/u...1780#Post161780

the block is still recessed so that wasn't changed prior to me (or by me although i thought about it before and am thinking harder about it now), but i'll see if i can get someone to measure my head to find out how close to 3.4 in thickness it is.

i'm glad i asked, although i'm afraid of what i'll have to pay to take care of it.
 
All this still makes me wonder what I have in my MKIII.
The engine is KF751HE. Seems to be slightly misleading to think it's an 8.0:1 and it's a H (High Compression?)block?
 
HE means non-recessed block, which would be a great distinction between the two blocks if they had the same pistons and head. mine is a UE which stands for emmissions block, which is recessed. this would be the lower compression block if everything else was the same between the two. the domed pistons make up for this, but of course, i don't have the domed pistons. looks like my recessed block is about to become non recessed.
 
after reading some info on compression ratio, i increased it with my overbore while decreasing it with the flat topped pistons. i'm going to measure my chamber volume and head height so i can calculate a ratio but what should i throw in for a head gasket thickness? i got a recessed bore one from BPNW, the one in the normal head gasket package.

what range of ratios should i be looking at for running regular unleaded well in my gt6?
 
Flinkly, you have a PM
 
Flinkly, the block you have KF10255UE is correct for the head you have 218225. Both are the later type, & for the GT6 domed pistons were used with that block & head. If you didn't already have the flat pistons, the thing to do would have been to just get domed pistons & off you go.

For a peppier engine, the best course would have been to just watch ebay & get one of the earlier engines. Then just skim the head.

I do not have any experience or detailed knowledge about procedure & measurements for decking the recessed block flat & then skimming the head for flat pistons. My guess is deck the block, then cc the head to guide skimming.

Dennis: You said your block # is KF751HE - is there a number missing from there?
 
The later KF series engines began with number KF1, so Dennis' engine number is probably correct as listed. That would make it a very early '71.
Incidentally, the Comm. No. on my '67 is KC5048LO, and the engine is KC5099E. Engine is definitely original to the car.
Jeff
 
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