Advice for putting a 2500 TC engine into a TR4a - does that make it a TR250 TC :-)

[SteveE]

Hi,

I am a new member to the club.  After 25 years of owning a Vitesse convertible I have finally upgraded to the car I always wanted a TR4a.

As I understand it the TR4a and the TR5 are very similar vehicles so it is entirely possible to swap in a 6 cylinder 2.5l.

I am sure there are people in the club who have done this swap and so can I ask for some advice please.

The work will be done by a local mechanic who used to work at the local Triumph dealership then at SAH here in Leighton Buzzard.

The 2.5l to be used is from a 2500 TC (estate) so it comes with twin SUs.  The engine has been extensively rebuilt inc. rebore and new valves.

Biggest questions;

• Do we swap just the engine or engine + gearbox (and OD?)
• Parts list – engine mounts, gearbox spigot
• I’m hoping we can bring across all the auxiliaries with the 2.5l such as starter motor, distributor, fuel pump etc.

Anything major I have not thought about ??

The final aim is to get the car to a fast road spec so fast road cam and rolling road tune is planned PLUS new suspension bushes, new grooved brake discs and good pads, sliding joint drive shafts

 

[John Morrison]

Hi Steve,

welcome to The Register and of course our forum.

You are correct that this conversion has been done, and I'm sure will make a brilliant car.

Overdrive I think will do fine, gearbox input shaft will need changing? to fit flywheel.

John.

[SteveE]

Thanks John.  I spent over an hour on the club stand at the NEC show last month and was made to feel very welcome to the club.  A number of people spent a lot of time with me and steered me away from some costly mistakes (I was planning to use triple webers but will now first try tuning with the SUs I have).

 

Edited December 20, 2022 by SteveE

[tr graham]

Engine mountings will need to fabricated to the chassis ,and I believe the torsion bar between the top of the turrets also , 

[John Morrison]

hi Steve, 

been thinking about your plans, ansd some decisions will depend on what you have.

e.g. even in A type form the overdrive is stronger from a TR than a saloon, so looking at your driving plans, its a TR Overdrive you want.

Gearbox ratios are the same, but the TR input shaft is larger diameter than the saloon one, you would need confirmation, but I think you could use the TR box, complete with shaft, and aTR Clutch driven plate, now it gets a bit vaque but hopefully with a redrilled flywheel a TR Clutch housing, propshaft should fit.As an alternative to not touching the engine, you could use the saloon box input shaft on the TR Box (T keepthe stronger overdrive)BUT you would be running with a smaller clutch driven plate 8.5 inch diameter as opposed to the TR 9 inch. dont think this would do you, the way you plan to enjoy your car.

Hopefully others will be along to correct/confirm this.

John.

[harlequin]

10 hours ago, John Morrison said:

hi Steve, 

been thinking about your plans, ansd some decisions will depend on what you have.

e.g. even in A type form the overdrive is stronger from a TR than a saloon, so looking at your driving plans, its a TR Overdrive you want.

Gearbox ratios are the same, but the TR input shaft is larger diameter than the saloon one, you would need confirmation, but I think you could use the TR box, complete with shaft, and aTR Clutch driven plate, now it gets a bit vaque but hopefully with a redrilled flywheel a TR Clutch housing, propshaft should fit.As an alternative to not touching the engine, you could use the saloon box input shaft on the TR Box (T keepthe stronger overdrive)BUT you would be running with a smaller clutch driven plate 8.5 inch diameter as opposed to the TR 9 inch. dont think this would do you, the way you plan to enjoy your car.

Hopefully others will be along to correct/confirm this.

John.

On my TR6 I have a CP (TR6) engine with a saloon gearbox and overdrive which has performed well for at least the last 100k. The clutch drive plate is from a saloon  and the overdrive output flange has an additional set of holes to match the TR  propshaft. I seem to remember having to turn the gearbox mounting plate around but cannot be certain and there was a bit of fiddling to get the gearbox exhaust bracket sorted. All in all a fairly straightforward swap.

Although I know none of the details one of my neighbours has a TR4 that is fitted with a PI engine from an estate car so the project is completely feasible 

George 

[elclem1]

The saloon engine with saloon gearbox is fine I have one fitted one to my TR6 track car and its as strong as anything. The only thing needed to change on the clutch is the saloon friction plate and as john suggests re-drill the output flange to take the propshaft flange i am not sure about fitting to a TR4a chassis but as previously said its been done before. I would do as you suggest and leave the SU's on for now you can always fit webbers later if required. Enjoy the changing over. Clem

[BlueTR3A-5EKT]

2500TC inlet manifold is machined to suit an engine that when installed is canted over, to get it all under the bonnet.  The TR uses an upright not canted engine installation.  The carbs will be aimed uphill to the engine with the TC manifold on an upright TR chassis install, so the float chambers on the SU carbs will need adjusting to get them level.   
What size are the SU carbs you have?  Were all 2500TC engines fitted with 1 3/4” carbs (4 studs attaching each carb) like the 2500S.   I recall the TC had 1 1/2” carbs.   (2 studs for each carb)

[harlequin]

18 minutes ago, BlueTR3A-5EKT said:

2500TC inlet manifold is machined to suit an engine that when installed is canted over, to get it all under the bonnet.  The TR uses an upright not canted engine installation.  The carbs will be aimed uphill to the engine with the TC manifold on an upright TR chassis install, so the float chambers on the SU carbs will need adjusting to get them level.   
What size are the SU carbs you have?  Were all 2500TC engines fitted with 1 3/4” carbs (4 studs attaching each carb) like the 2500S.   I recall the TC had 1 1/2” carbs.   (2 studs for each carb)

Thats a good point but I imagine that every TR dealer has several US spec TR6 manifolds laying around for not much money 

George 

[BlueTR3A-5EKT]

16 minutes ago, harlequin said:

Thats a good point but I imagine that every TR dealer has several US spec TR6 manifolds laying around for not much money 

George 

I would not bank on it.   There are two types of US spec inlet manifold and you want the post 1973 item that is shaped  like the 2500S inlet but machined for vertical installation.   The earlier TR manifold will fit but the inlet ports are closer together so it fits to a different cylinder head.

[harlequin]

21 minutes ago, BlueTR3A-5EKT said:

I would not bank on it.   There are two types of US spec inlet manifold and you want the post 1973 item that is shaped  like the 2500S inlet but machined for vertical installation.   The earlier TR manifold will fit but the inlet ports are closer together so it fits to a different cylinder head.

Yes the TR250 item is of no use in this case,  I have been using a 1972 manifold without problems, but I have heard that the later ones are better. May be easiest to get the original job machined to suit.

I know TRGB have a selection of  US manifolds in their junk loft, so worth a call and I expect Conrad has one or two laying around as well.

George 

[stuart]

Ive got a later carb manifold here if required.

Stuart.

[FatJon]

From rebuilding a TC engine for my TR6:

You will need the tr6 engine backplate or the engine will lean to one side. The TC engine mounts are integral with the TC front plate so you’ll may be better off with a TR5/6 front plate too.

 

[elclem1]

I seem to remember I cut off the mounts on the front plate and replaced the rear plate.  I also run mine on webers so not sure about the SU set up.  Clem

[Malbaby]

I think you will may have to weld plates onto the front of he towers to fit the tower brace...Or fabricate a new one, as it has to be more forward to clear the 6cyl engine.

Also the steering rack has to be moved forward.

If you plan to run a factory exhaust manifold, try to obtain one with the twin outlets [semi extractor]. Fit a 2 into 1 collector onto the flange and run a single/larger exhaust pipe to the rear muffler/mufflers.

[SteveE]

Ok so the project is now underway so all your advice is coming into sharp focus.  Firstly thank you all for your help and info. which is invaluable.

To mate the Triumph 2500TC saloon engine to the TR4a gearbox is looking tricky as the clutch and flywheels are quite different as per the photo below.  The TR parts are on the right.

ANY suggestions welcomed!  If we can find a centre plate with the right spline and not too much hub, we can drill the adapter plate to suit most of  the bell housing holes and drill the bell housing for the top three block studs.

Cheers Steve

[rcreweread]

Steve - I am no expert but for what it's worth, this is what I believe is the case - the TR gearbox casing is pretty much identical to the saloon one so it should fit straight onto your saloon engine ( previous posts have talked about changing the engine plate/mountings so the engine isn't canted over because if it was, then so would the gearbox which would create lots of problems, not least with your gearstick!

The saloon clutch plate is 1/4 or 1/2 inch smaller ( I can'rt remember which!) in diameter than the TR one and it has a smaller diameter input shaft size and different splines so you will need to use a TR centre/clutch  plate. The flywheel connecting bolt pattern pattern is different on the two clutches - if you use the saloon flywheel, it will need re-facing to match the diameter of the TR centre/clutch plate, or alternatively get the TR flywheel redrilled to match the saloon mounting holes PCD - I believe the clutch covers have the same mounting holes so you could use the TR one or again, get the saloon one refaced so it matches the overall diameter of the TR clutch plate- I think the TR clutch fork, CRB and carrier should work ok.

Bearing in mind a lot of people use a saloon gearbox in a TR and all you have to do then is use a saloon clutch plate inside your TR flywheel/clutch cover, then the converse you are proposing should be simple as well.

Hope this helps

Cheers Rich 

[SteveE]

11 hours ago, rcreweread said:

Steve - I am no expert but for what it's worth, this is what I believe is the case - the TR gearbox casing is pretty much identical to the saloon one so it should fit straight onto your saloon engine ( previous posts have talked about changing the engine plate/mountings so the engine isn't canted over because if it was, then so would the gearbox which would create lots of problems, not least with your gearstick!

The saloon clutch plate is 1/4 or 1/2 inch smaller ( I can'rt remember which!) in diameter than the TR one and it has a smaller diameter input shaft size and different splines so you will need to use a TR centre/clutch  plate. The flywheel connecting bolt pattern pattern is different on the two clutches - if you use the saloon flywheel, it will need re-facing to match the diameter of the TR centre/clutch plate, or alternatively get the TR flywheel redrilled to match the saloon mounting holes PCD - I believe the clutch covers have the same mounting holes so you could use the TR one or again, get the saloon one refaced so it matches the overall diameter of the TR clutch plate- I think the TR clutch fork, CRB and carrier should work ok.

Bearing in mind a lot of people use a saloon gearbox in a TR and all you have to do then is use a saloon clutch plate inside your TR flywheel/clutch cover, then the converse you are proposing should be simple as well.

Hope this helps

Cheers Rich 

Thank you Rich.  Very helpful. Cheers Steve

[BlueTR3A-5EKT]

If you intend to use the estate car overdrive gearbox do not forget the speedo ratio output is wrong for the TR speedo.

Get the estate speedo and strip it to get its guts to fit in a TR speedo.   It will be a lot closer reading speed wise than if you had not done it.

Have you read this about fitting a saloon/estate overdrive in a TR chassis?  On an IRS you have the option of hacking off the existing chassis mount brackets and moving them down /rearwards.

 

Edited February 25, 2023 by BlueTR3A-5EKT

[BlueTR3A-5EKT]

On 2/21/2023 at 10:37 AM, SteveE said:

Ok so the project is now underway so all your advice is coming into sharp focus.  Firstly thank you all for your help and info. which is invaluable.

To mate the Triumph 2500TC saloon engine to the TR4a gearbox is looking tricky as the clutch and flywheels are quite different as per the photo below.  The TR parts are on the right.

ANY suggestions welcomed!  If we can find a centre plate with the right spline and not too much hub, we can drill the adapter plate to suit most of  the bell housing holes and drill the bell housing for the top three block studs.

Cheers Steve

Now gives us a photo of the gearbox that went with the LH clutch parts.   That driven plate looks like it has too fine a spline for a saloon/estate original gearbox.   The RH clutch looks about correct for an orig TR unit.