1973 GT6 Restoration

[DJB350Z]

I started out driving and working on Japanese cars with my dad when I was first able to drive. I always liked the Datsun 240/60/80z and for a few years had been scouring the internet for a suitable one but even for a restoration the prices are out of my reach.

When I saw a GT6 online for the first time I thought they looked really quite nice, with a similar kind of shape as the Datsuns. So last year I extended my garage to make some extra room for a project car, and since I’ve been looking out for something to fill the space.

I looked at a few, and chickened out of 1 or 2 that I just realistically couldn’t deal with because of bad rust. Then, I saw one come up for sale at a company that restores TRs. The advert pictures didn't look great but as soon as I saw her I knew she was a good find.

She was a stalled restoration project, bought for £450 in 1997 and worked on up until 2005 when I presume that she was stored away in a garage until this year. Everything was stripped off, not labelled and stored in boxes.

The PO to that had the car for 10 years, and the one before that 4 years. There’s history/receipts going back to 1979, and as far as I can work out about 113k miles driven. However, the engine was swapped early on for a 2.5 from a 2500 so who know’s how many miles that’s done.

There’s been many new panels fitted, chassis cleaned up and painted, new suspension and brakes overhaul so underneath looks spot on. New tyres all round and refurbished alloys too - I don't know if the alloys are factory originals or else?

Overall, I’m super chuffed with my purchase and can’t wait to get started!

[DJB350Z]

The car was loaded up onto a transporter last week with ALL of the parts strategically stowed away inside the cabin. It’s amazing how much you can actually fit in there. I drove up and collected just a few pieces of glass from the doors and quarters.

Now it’s time to unpack, decipher and catalogue. Yikes.

There’s so many parts.. I recognise probably 70% of them but since I’ve never owned a classic, nor a Triumph this will be some lego project to reassemble them! There’s new bits, old bits etc. The PO seemed to keep everything just in case. There also seems to be some cases of having a part of a pair, and multiple spares of a part you only need one of. E.g. 3 headlights, 6 headlight bulbs and 2 glass sunroofs. But, 1 door handle.

Some things I noticed that are missing include a steering rack (I possibly have gators), indicator stalks and a flywheel.

[DJB350Z]

I’ve got everything out of the car now and I will post some photos of the inside soon. The engine was big and heavy but I managed to safely pull it from inside the cabin.

Also, the gearbox is out but unfortunately it looks like there’s a hole in the bell housing. I haven’t identified the box yet so it could be original GT6, 2500 or something else. All I know is that it has overdrive. Oh.. and 2 gear knobs.

[DJB350Z]

I’ve moved the engine onto a bench to clean up and inspect.

The engine block is a 2.5 from a Triumph 2500. It's number is MG18382HE, but the cylinder head has a number (516816) that I think didn't originally come with the block. When I look up 516816 it says: "Mk1 PI & Mk2 PI to MG50000 2000 low comp 7:1. TR6 to CR2845".

I’m unsure if this engine block, cylinder head and gearbox was installed and running in the car at some stage all together. I want to try and make sure at least the block and head are compatible with an acceptable compression ratio before I start rebuilding it. If anybody knows about this please let me know. I should hopefully be hearing from a specialist later in the week about whether the head and block will work nicely together.

Before pictures

After/In progress pictures

[DJB350Z]

During the cleaning of the engine block my dad and I spotted a couple of issues. One of the core plugs has a small hole in it:

Another of the core plugs looks so damn shiny I'm guessing it's been replaced. Probably explains the big patch of surface rust in one of the above photos where it failed previously. I think in amongst the spare parts I have seen a set of new core plugs so I can only assume the PO fitted 1, but left the others. So, I will as due diligence replace all of them with new items. I read somewhere that even though they look ok from the outside, it's from the inside out that they fail.

The other issue, is this bolt on the gearbox side is bent. No drama, but good to spot now:

We're going to continue cleaning the block up as much as possible whilst we find out more about the engine and head combination and if they'll play nice together.

I'm hoping we can get to a stage in the next day or 2 where the bores are clean enough to safely turn it over by hand / with spanner / with big bar.

[johny]

Looks like a standard 3 rail OD gearbox for a GT6 to me and that bell housing hole shouldnt give any problems. It will have a number stamped on the top face, right hand side edge of the cast iron case which will identify exactly what it is assuming the internals havent been swopped.

Also the head number seems to correspond with the engine number so indicating the whole unit comes from a mk2 PI 2.5. Its quite a common upgrade but means when alls done you will have treat the accelerator with respect both for maintaining control of the vehicle and to reduce the risk of early diff, driveshaft and gearbox failure👍

[JohnD]

A "low compression" head will have the larger combustion chamber, so probably safe, but you are quite correct to want to measure that volume to be sure.

Are you familiar with the burette method?   If not, please see: https://sideways-technologies.co.uk/forums/index.php?/topic/7551-how-to-raise-the-compression-ratio-safely-and-effectively/#comment-99739

 

JOhn

[johny]

From the head number Im taking it as giving low compression when fitted to a 2000 but would imagine when installed on a 'Mk1 PI & Mk2 PI to MG50000' 2.5 block it will give the higher compression associated with the more powerful engine. Sounds logical doesnt it?

[DJB350Z]

38 minutes ago, johny said:

Looks like a standard 3 rail OD gearbox for a GT6 to me and that bell housing hole shouldnt give any problems. It will have a number stamped on the top face, right hand side edge of the cast iron case which will identify exactly what it is assuming the internals havent been swopped.

Also the head number seems to correspond with the engine number so indicating the whole unit comes from a mk2 PI 2.5. Its quite a common upgrade but means when alls done you will have treat the accelerator with respect both for maintaining control of the vehicle and to reduce the risk of early diff, driveshaft and gearbox failure👍

Just checked and the stamp reads KF12292.

Yes, I had the same warning to not dump the clutch at the lights! Are there any diff upgrades like Quaife etc. worth investigating?

[DJB350Z]

19 minutes ago, JohnD said:

Are you familiar with the burette method?  

My dad is but he never had to do it on his old Lotus Cortina. I will read that link and see if we can work it out.

 

Thanks

[johny]

9 minutes ago, DJB350Z said:

Just checked and the stamp reads KF12292.

Yes, I had the same warning to not dump the clutch at the lights! Are there any diff upgrades like Quaife etc. worth investigating?

says that the gearbox was originally fitted to a USA GT6. I doubt your car is an import so more likely a replacement gearbox was fitted at some stage. Theres also a serial number on the underside of the diff which should indicate the ratio - important as it would be nice to have the highest ratio available (3.27:1) for a 2.5L engine.

Strengthening the drive train isnt easy (so not cheap) as the components have just about been taken to their limits for the 2L engine and theres not much room to get in anything beefier. However youre in the best place for getting help...

[Pete Lewis]

2 hours ago, DJB350Z said:

"Mk1 PI & Mk2 PI to MG50000 2000 l

mk1 has 3/8  stud holes and external pusrod tubes  Mk2 has 7/16 studs  and enclosed pushrods 

cant see the two being compatible unless the early MK1  PI  used a Mk2 head   

Pete

[johny]

In the photo its definitely a mk2 head and the engine serial number MG seems to indicate mk2 PI so I think its probably the original head of that engine and should give the correct comp ratio of 9.5👍

[DJB350Z]

40 minutes ago, johny said:

says that the gearbox was originally fitted to a USA GT6. I doubt your car is an import so more likely a replacement gearbox was fitted at some stage. Theres also a serial number on the underside of the diff which should indicate the ratio - important as it would be nice to have the highest ratio available (3.27:1) for a 2.5L engine.

Strengthening the drive train isnt easy (so not cheap) as the components have just about been taken to their limits for the 2L engine and theres not much room to get in anything beefier. However youre in the best place for getting help...

So I just slithered underneath to read the differential stamp. Quite hard to make out as PO was generous with the black paint but I can see that it starts with KD.

[johny]

ok thats the correct ratio for a standard OD GT6 (3.89:1) but might be a bit low for your set up. It means it'll certainly accelerate and you wont really need 1st gear but wont be as low revving on motorways as it could be - anyway youre a way off worrying about whether you need to change it yet😁

[DJB350Z]

I like to plan ahead!

[NonMember]

2 hours ago, Pete Lewis said:

mk1 has 3/8  stud holes and external pusrod tubes

Only on the 2L - this is a 2.5 engine so the larger studs and full-width head were used from the start

[johny]

Good to know, thanks. Not much difference between mk1 and 2 PI engines then although I see power was down slightly in the later one?

[NonMember]

There was a cam profile change at some point - I think the same time that the GT6 cam was detuned - PI saloon and GT6 use the same camshaft IIRC.

[DJB350Z]

My dad managed to clean the bores up and we're able to safely and smoothly turn the engine over by hand. The bores weren’t actually terrible in the end but look significantly better now.

Of course as this engine is a 2.5 I’ve been reading some things about the oil sump. GT6 one needs hammering from the inside or if it’s the 2.5 sump then some modification to the cross member is required.

Someone on another thread (I’ve forgotten where) said that mine looks like a GT6 oil sump. Well, here are some closer pictures.

Of the 23 sump bolts that came out there were a few different lengths. Is that correct?

We removed the oil sump to reveal the crank which looks like a standard item, perhaps the same as one from a GT6. The casting numbers are 311313, 17740J and JGSB.

We took one of the big end caps off to check for wear. We think it looks ok, but wondered about your opinions.

Another question - the bottom of each end cap has been scored 'E.g. IIII' to denote its position #1-6 like in the photo below. Is that a normal thing, or could it be a clue that PO had these replaced at some stage?

That's it for today. I've now got the unfortunate job of cleaning up the oil sump!

[NonMember]

40 minutes ago, DJB350Z said:

Someone on another thread (I’ve forgotten where) said that mine looks like a GT6 oil sump.

It has a slanted bottom, which the GT6 one doesn't. That suggests it's from a saloon, where the engine sits at an angle.

 

41 minutes ago, DJB350Z said:

Of the 23 sump bolts that came out there were a few different lengths. Is that correct?

Yes, and it's very important to put the right ones in the right hole or you'll strip the thread in the alloy bits front and back.

42 minutes ago, DJB350Z said:

The casting numbers are 311313,

That should be a 2.5 PI saloon crankshaft.

43 minutes ago, DJB350Z said:

the bottom of each end cap has been scored 'E.g. IIII' to denote its position #1-6 like in the photo below. Is that a normal thing, or could it be a clue that PO had these replaced at some stage?

It suggests they've been taken off at some stage, by someone who knew to keep them with the right conrod.

[johny]

Cranks are different as thats where the increase in capcity comes from - longer stroke not bigger bores. Remember the engine had already come from 1600cc in the first Vitesses.

Looks like a 2.5 sump as believe the GT6 has an indentation in it but this would be hit by the 2.5 longer throw crank.

Bearing does look pretty good - no sign of copper under layer? To be completely sure you have to measure bore diameter when two halfs bolted together and compare it with crank diameter to see if clearance is within spec (and crank isnt oval!). If you look at the back of the bearing you should see if its standard size or the crank has been reground.

You really need to get hold of a Triumph workshop manual, the GT6 is available free online but not sure about 2.5PI...

[chrishawley]

Sump pan: See below photo of a GT6 pan. Note that it is very skinny on the front extension and is rebated to sit over the steering rack. In the fitted condition there can be gnats all clearance between the sump and the rack even when everything is standard. The deep, saloon,  sump doesn't fit (I have teeshirt for that).

So, has to be a GT6 'skinny' sump. But depressions will have to be formed (press/beat)  to accomodate the crankshaft throw on cylinder #1 and #2. #1 position is hardest because it's adjacent to rebate for the steering rack. #3 may need a tickle as well.

Ops manuals for 2500 are not rare but there's one on ebay for £15 with no bids. Ends in couple of hours.

https://www.ebay.co.uk/itm/165613613374?hash=item268f57313e:g:BngAAOSw13ti7VZO

 

[DJB350Z]

Thanks for the 2500 manual find. We have a Haynes for the GT6.

[chrishawley]

3 hours ago, DJB350Z said:

Thanks for the 2500 manual find

£14.79 that was a snip! I paid WAAAYYYY more for mine.