Our Cars : Richard Truett’s Triumph Stag – Part 3

Richard Truett

Triujmph Stag straight-sixRA

Not long ago, I leaned over the wing, looked into the Stag’s engine bay and all I saw was an abyss.

Nothing fit.
Nothing worked.
Nothing lined up.

Installing the proven and reliable Triumph 2.5-litre six into the Stag was the easy part of my summer Stag project. And it is where my good luck ended. Because just about everything since then has been a struggle.

I knew already the 2.5‘s starter and alternator were on opposite sides as the Stag V8, so wiring would have to be fabricated. However, I expected no major problems from the clutch hydraulics, power steering system, throttle cable, radiator and hoses, cooling fan — but all of that and more needed major sorting.

Further complicating matters were the tubular exhaust and my special triple carburetor set up. After a solid week of slow or no progress, I contemplated removing the 2.5 engine and just using a rebuilt Stag V8  I have in another car. But slowly, I began to score small victories and get the project moving again.

Installing the straight-six into the Stag
Installing the straight-six into the Stag

One thing I’ve learned about Stag restorations is that the more components you install, the more difficult the car is to work on. Room for wrenches and access to parts disappears quickly. And that’s certainly what happened when the engine and ‘box were installed. That part of the job was easy.

In fact, of all the engine installations I have ever done, none went faster or smoother than mating Triumph 2.5-liter six to the Stag. The engine and manual gearbox were placed on a wheeled dolly. I put jack stands under the car, removed the front suspension, and, after undoing the oil filler cap, the powertrain just cleared the Stag’s front apron and slid directly under the mounting holes in the frame rails.

Then I attached chains to the lifting eyes and connected up the engine to a hydraulic hoist. In less than 15 minutes the engine and box were raised into place and bolted in. I used the front and rear engine mountings from a 2500S and was astounded at how nicely everything fit together in the Stag. All the holes in the frame rails were there and in the exact places. Same with the rear mounts. Two hours later, the Stag was back on all four wheels with its new smaller, but more reliable engine and rebuilt overdrive gearbox in place.

Starting, then, with the power steering system I had to solve numerous problems. The Stag power steering hoses available from Rimmers and others are too long and not shaped properly. I could find no LHD Triumph 2500 hoses, so I had to modify the Stag hoses. My first attempt ended in disaster and I ruined both hoses, an expensive lesson. I got it right with the next set. But the PAS pump is sitting about 2mm off the frame rail and hopefully won’t touch when the engine is running.

Engine now in place and the plumbing is underway
Engine now in place and the plumbing is underway

Progress came by figuring things out and trying different combination of parts, new, used or from other vehicles to determine what works best and looks professional I dug deeply into my store of spares collected over a decade.

If I just wanted to put the 2.5 in the Stag and get it going with no regard to appearance, I could be done by now. But from the start of the project, the one goal was to make the car not only function well, but have all the mechanical bits really buttoned down and factory looking.

The cooling system, for example, uses TR7 parts that look like they belong in the Stag engine bay. From a 1980 TR7, I used the overflow tank and mount, which fit the Stag’s inner fender well perfectly and look like Triumph put it there. The fan blades are TR7, too. They nicked the nose of the 2.5‘s water pump — until the blades visited the business end of a bench grinder and were shortened about 1/4 inch. The top hose comes from a 1992 Plymouth Laser.

The three-carb set up uses a mechanical linkage from a Federal spec TR6. But the Stag has an accelerator cable. A combination of an adjustable TR3 choke turnbuckle, a Rover 827 throttle cable, and  Mini Cooper linkage worked a charm to meld the two systems.

The GM alternator would not fit due to interference with the top of the front engine plate. A high-revving Dremel swooped in and solved the clearance problem. A standard Stag alternator arm worked perfectly with the GM alternator. And it looks great in the Stag engine bay.

Despite some morale crushing setbacks, re-assembling the Stag has been the most fun old-car adventure I have ever had. Some days, everything you touch is magic. Other days, you spend hours fiddling with something like a clip on weatherstrip on the door or the chrome windscreen trim.

The seas are now retrimmed and in place
The seas are now retrimmed and in place

It was joy trimming and installing the carpet and installing the rebuilt seats and the rest of interior trim. With the entire dash board assembly out of the car, it was easy to not only fit the carpet, but  attach it so that it is tight and stays in place. The key is to place the edges behind and underneath things and use the odd snap and velcro strip. Reproduction carpet kits are not the best fitting, so a tape measure and sharp razor blades, strong glue, and plenty patience is necessary to do a good job.

And so it goes. Each week the list of problems grows smaller and the Stag inches closer to being ready for testing. The lesson here is that when swapping engines, the most difficult part of the job may not be bolting the engine to the car, but connecting up all the plumbing and electrical items so that they look factory installed and are safe, reliable and durable.

New carpets look very inviting
New carpets look very inviting
Keith Adams


  1. Interesting to watch a straight-six go into a Stag. I know a bloke who is about to remove one. It’s originally from a BMW 3.0S, IIRC, and he will install a rebuilt Stag V8 in its place.

    The list of parts from other vehicles reads a little like that for the (almost complete as I type) installation of a ZF 4HP22 in my Rover P6B.

  2. ZX 4HP22? hope it came from an XJ40 and not anything else! it’s notorious for burning out clutch packs. There is a mod to releive pressure on the 1st/revers clutch pack which should be carried out on all of them, Jaguar applied it from new hence my comment. Although the XJ40 version has no drive for the speedo

  3. The only fault I know on the six-in-line is the crankshaft thrust washer. Those triple carbs look neat. #1, one of my colleagues has done the reverse, and put a Rover V8 into an old BMW 5-series.

  4. Was there a reason for using 3 Strombergs ? Wasn’t a twin HS6 setup from a 2500S or TR250 more likely to produce satisfactory results , and be easier to link up ?

  5. Its a real shame you didn’t work for BL back in the day.

    What an amazing attention to detail.

    Using a GM alternator is genius, the Lucas (prince of darkness) are a PITA, the GM CS types are atom bomb proof.

  6. Very interesting, IIRC the Stag was (very loosly) based on the 2000 monocoque so I guess some dimensions will be the same.

  7. @Stewart: it’s a portmanteau contrived from a Land Rover box with a BMW output shaft and tail housing. Some unfortunate Jaguar XJ40 donated its output yoke and shift cable. I have rebuilt the box including all the recommended mods, but you might be surprised to know that both my donor boxes proved to have clutch packs in excellent condition, despite their age and mileage. The 4HP22 is not as bad at blowing clutches as the legends suggest. All the details on the conversion have been accumulating on the Classic Rovers Forum (http://www.classicroverforum.net/viewtopic.php?f=1&t=15069).

  8. Looks great Richard..
    Can’t wait to see it again this Saturday.
    Hopefully you will be there again for a bit
    and we can visit again..You are homestretch
    now Bro..

  9. @6, not loosely based, entirely based upon. All chassis hardpoints the same as a Mk2 2000, apart from the wheelbase (so shorter prop on the Stag). I’ll be interested to find out how well those triple carbs work, often drooled over them on the Goodparts site when I had my 2500S. Is it an S engine? Have you lowered the compression ratio and changed the cam? I’d say that would be a neccessity to take advantage of the triple carbs (certainly if you’re looking for performance to get close to the Stag @ 140 bhp). Great stuff though.

  10. I had a Stag with a bog standard 2.5s engine fitted, with twin carbs, after the previous owner got fed up with the original lump. Stag V8 is the spawn of Satan, one of the finest own goals ever scored by the British motor industry

  11. @12
    We had a Stag with the V8 and standard rad. We ran it every day, went on holiday in it without problem for around 9 years. The body rotted away in the end but the motor was trouble free.

  12. 11. Thanks Allen, I knew the Stag project started out as a SWB version of the 2000, but I wasn’t sure how much was left by the end of the development, I as understand there was some “camelisation” along the way.

  13. Triumph had at least one straight six Stag prototype running, a 150bhp PI version would have been a lovely motor (even with the later 130bhp engine) but Federal emissions regs probably put paid to such a model. A shame as it could have saved the reputation of both the car and the company.

  14. I feel performance will not be down much on the Stag’s original V-8.
    First, I have fitted the engine with a TR5 cam. The tubular exhaust and additional carb should see a nice boost in power.

    I have also raised the compression by having 40 thou shaved off the head. I am hoping for around 140 horsepower and decent torque.

    I am well aware of the 2.5’s thrust washer issues. Over here in the U.S., you can buy thrustwashers that are 30 percent larger and that solves the problem.

    I am not close yet to having her roadworthy. It’ll be awhile yet. I bought the car from someone who took it apart 30 years ago. And so, it needed plenty of sorting other than the powertrain.

  15. I used to have a pretty poor outlook on Triumph 6s in Stags, but since learning that they originally intended to release a a 6-cylinder Stag alongside the V8 I’ve become rather a fan of them.

    Your installation looks great too. I’d be willing to bet that a triple-carbed 2.5l would make close to if not more power than the stock V8.

    My personal Stag build idea is to try and make the Stag Triumph would have made had it decided to gun for the BMW 3.0 CSL. What that would entail I haven’t decided on yet.

    I’d keep the original V8 (mainly because I like a challenge) and then I’ve got 1 of 3 ideas, ranging in complexity and difficulty.

    The first is to adapt the Lucas mechanical fuel injection to the Stag V8, as was intended at one point in the Stag’s gestation.

    The second is to convert it to run on ITBs. I’ve heard ones from a GSXR 600 are the best match.

    The last one is to convert two Dolly Sprint 16v heads to fit the Stag V8, also running fuel injection.

    While technically possible, the last one would be fiendishly difficult. Among other things, it’d involve reversing the rotation of one of the camshafts, probably a revers casting of a 16v head and the modification of some of the oil and water passageways.

    The payoff would be utterly fantastic though. Not only would I have a very fast Stag, but it’d probably be closest to what the Triumph engineers would have attempted at the time.

    There’s a good discussion about a 32v Stag engine here: http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1282231557/

  16. @18 I recall a Stag article showing the V8 with sprint heads fitted. It was done by using two sprint heads with the RH one being turned so the the chain housing was at the rear. This was then cut off and welded to the now front of the head. It may have been carried out by Hart Racing. I can’t recall any further information. Now of course, I will be searching for the article. LOL.

    Regarding reliablity, I always meant to tell the story of my 34 years so Stag ownership. It’s a colourful tale so here’s a concise version.

    In July 1980 I swapped an immaculate P reg Spitfire with hardtop & overdrive for my 1973 Stag.

    The engine must have had a dose of piston seal as after a month or two the oil consumption went up to 5 ltrs every two weeks. I used to save the dirty oil from servicing customers cars and put that in !! A ltr of water required for each journey, but it never let me down, and being a young man it used to get the cobwebs blown out on a regular basis.

    I used it everday for the first 5 years, then the use of a company car allowed the Stag to become a part time car.

    A year or so later I put in a used Triumph V8 after giving it a crank grind and a set of rings. That was supposed to be a stop gap for 12 months until I reworked the original engine. Well, the used engine is still in the car today and has taken us to Scotland and the Lakes District on a regular basis. It’s never overheated and sits at thermostat temperature in traffic.

    I will say this, make sure the waterways in the block are clear, I got over a cup full of silt out of each bank before reassembly.

    In my experience the Stag V8 can be reliable.

  17. @21 That rings a bell as well, and sounds much easier than a custon casting. I wonder how they sorted out the cam rotation. Probably a gear below to reverse the direction. If you can find anything I’d be very grateful 🙂 I’ve looked myself but haven’t found anything.

    I’ve heard stories of people rebuilding Stag V8s and finding oodles of clag in the waterways. I wonder how much of their reputation for overheating is due to that.

    I’d love a Stag myself, although I don’t think I’d trade my Spitfire for one. I’m in the middle of restoring it and swapping in a breathed-on 2.5l Triumph I6 (plus assorted lightweight goodies).

    Should be a bit of a pocket-rocket, and a very nice complement to a GT Stag 🙂

  18. How are you getting along with this lovely car?

    This is the only BL car I have ever hankered for.

    Yours will be better than the factory ever hoped 🙂

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