Triumph Stag - Rover V8 Engine conversion

Honest John Back Room » Technical matters
View Threaded
Mon 19 Jan 2004 15:52
Triumph Stag - Rover V8 Engine conversion - pies1961
Hi
has anybody got any experience of this ? I heard you can retain your stag manual gearbox and connect to Rover V8 via an adaptor plate, is that true or bunkum ? If true do you know where I get the plate from

If not anybody know any good breakers with Rover gearboxes including bellhousing ?? cheers

Edited by Pugugly on 29/09/2008 at 23:55

Reply | Report as offensive | Link
Mon 19 Jan 2004 16:32
Triumph stag rover V8 Engine conversion - robert
8< snip 8<
Reply | Report as offensive | Link
Mon 19 Jan 2004 18:53
Triumph stag rover V8 Engine conversion - Cliff Pope
It's a very common conversion, especially a few years ago when original Stag engines seemed so temperamental. I think it involves a special bellhousing, to mate the original gearbox to the Rover engine, or you can use the whole Rover set-up. Contact the Stag Owners Club, they will know all the details.

It is a less desirable conversion now, because having the proper engine commands a premium. Enthusiasts are keener on originality now. Also better knowledge of the various factors such as cooling and water circulation mean that the Stag engines have been found to be not so bad after all.
The Rover engine is much lighter, so I think there are handling issues to look at too. But SOC will know it all.
Reply | Report as offensive | Link
Mon 19 Jan 2004 20:13
Triumph stag rover V8 Engine conversion - andy n
this is meant to be a \"grown ups\" forum robert, if you cannot post a intelligent reply to this question why post at all?


{Quite. That\'s why I\'ve deleted his comment. DD}
Reply | Report as offensive | Link
Mon 19 Jan 2004 20:42
Triumph stag rover V8 Engine conversion - Cambridge
Think long and hard before doing this.

You will be halving the value of the car.

I would spend the time and effort in getting the Triumph unit working correctly.

With regular coolant changes and some basic care the Triumph engine can become nice and reliable.

That said, if the car does not have an engine, finding a decent Triumph unit will be difficult, while Rover/Buick V8s are pretty common.

I echo earlier advice - talk to the Stag Owners Club or the Triumph Sports Six Club.

Good luck.
Reply | Report as offensive | Link
Tue 20 Jan 2004 08:33
Triumph stag rover V8 Engine conversion - NARU
If you really, really want to do this conversion I suggest you advertise in one of the classics magazines - someone, somewhere will be keen to take their car back to original and will probably do a straight swap with you.

I'd recommend talking to a real Triumph engine specialist before doing anything drastic. A lot of people claim the design flaws of the stag engine have now been fixed, and they probably are if you're prepared to live with oil changes every 3,000 miles and new timing chains every 25,000. SOunds terrible, but if you only do 3-6,000 miles a year its not too bad.

Reply | Report as offensive | Link
Tue 20 Jan 2004 08:40
Triumph stag rover V8 Engine conversion - disco2andy
The rover engine ruins the handling, it also requires cut down carberettors or a large bulge on the bonnet. If you do not have the original engine I would suggest using a truimph 2500 engine, same weight, reasonable performance and best of all bolts straight in - it was the engine the car was originally designed to use.

Andy
Reply | Report as offensive | Link
Tue 20 Jan 2004 08:41
Triumph stag rover V8 Engine conversion - Cliff Pope
Oil change every 3,000 miles is a sensible thing to do with any classic. Timing chains last much longer than 25,000 miles, and in any case they give warning of wear by rattling, unlike belts which just snap.
Someone mentioned fuel economy. The Stag I had did 29 mpg driven carefully, much better than the Rover engine.
Reply | Report as offensive | Link
Tue 20 Jan 2004 15:38
Triumph stag rover V8 Engine conversion - Galaxy
I've also heard stories of people fitting Wankel Rotary Engines into Stags.
Reply | Report as offensive | Link
Tue 20 Jan 2004 20:04
Triumph stag rover V8 Engine conversion - Dude - {P}
I stand to be corrected on the original Stag engine, but I seem to recall the main problem with this engine was that there were only 3 main bearing journals, which then resulted in crankshaft whip and eventual breakage at high revs.
Reply | Report as offensive | Link
Wed 21 Jan 2004 21:15
Triumph stag rover V8 Engine conversion - Dizzy {P}
The Stag engine had a five-bearing crankshaft, which I think is correct for a V8. It is sometimes said that the crankshaft was weak because there was too little journal overlap but I don't recall a big problem with crankshaft breakage.

There were lots of other problems such as poor aluminium casting quality, timing chain stretch, valve spring breakage, etc., but it appears that all this has been sorted out now and a Stag engine that is carefully maintained is pretty reliable.

If the ex-Buick Rover V8 hadn't belonged to Triumph's direct rival we might have seen it in the Stag. However, some say the Stag engine is sweeter than the Rover V8 and it is a fact that Stags with the original engine are more highly valued than those with replacement engines. I agree with those who recommend keeping to the Stag engine if at all practicable.
Reply | Report as offensive | Link
Thu 22 Jan 2004 09:09
Triumph stag rover V8 Engine conversion - Dude - {P}
Dizzy - I agree 5 main bearings is the norm for a V8 engine, but the Stag engine was the result of two Dolomite Sprint blocks combined to make the one unit, and I think I could still be correct in thinking that the Sprint engine only had 3 main bearings. Would appreciate if somebody could confirm this point one way or the other.
Reply | Report as offensive | Link
Mon 29 Sep 2008 23:40
Triumph stag rover V8 Engine conversion - rogerroutemaster
I can confirm that the Triumph Sprint engine has FIVE (5) (Cinq) main
bearings
Reply | Report as offensive | Link
Tue 30 Sep 2008 00:42
Triumph stag rover V8 Engine conversion - cheddar
the Stag engine was the result of two Dolomite Sprint blocks combined to make the
one unit and >>


Not so much Sprint, more 1850, the Stag head design was based on the 1850 and the cam chain was simplex as per the 1850 where as the Sprint was duplex IIRC.

The above suggestion of fitting a 2.5 straight six is a good one, I think a Sprint engine will also mate onto the Stag box.
Reply | Report as offensive | Link
Thu 22 Jan 2004 09:16
Triumph stag rover V8 Engine conversion - John S
Dizzy

Yes, the Stag did have a 5 bearing crank. Bearing wear and low oil pressure were common - I believe due to a combination of marginal sizing of the main bearings, the quality of lubricants at the time and the then long 6k service interval. They seemed to run like this for ages though, and I never heard of a crankshaft actually breaking.

The cooling system was another weak point, again being of marginal capacity. A summer trip in a Stag was fraught with anxiety if traffic was encountered.

Timing chains were also a common failure area, as were head gaskets, due to the infamous sloping head studs. Had all these problems on my Stag!

I saw a number of Rover V8 conversions. The bonnet bulge was common, but was avoidable by using a Holley carb and manifold, or (I believe) an MGB V8 manifold which set the carbs further back. The Rover engine is much lighter, and has a peak power point nearly 1000 rev/min lower than the unique Stag V8. This makes it less than an ideal match for the transmission, unless it's a manual with overdrive. The non-overdrive manual and particulary the auto were, I thought, very low geared, given the engine size.

I have to say I parted with mine with little regret.

Regards

john S
Reply | Report as offensive | Link
Sat 24 Jan 2004 19:42
Triumph stag rover V8 Engine conversion - Andrew Moorey (Tune-Up)
If you are going to replace the engine anyway why not consider a small block Ford or Chevy. Cheap to buy in standard form, oodles more power, Iron block with alloy heads to help with the weight issues and a proper V8 burble to boot! Couple it to a slush box for effortless cruising. I know, I know, the originality goes out of the window but at least it will have the power to match the stunning looks, shame about the handling, and the brakes....
Andrew ;-))


Simplicate and add lightness!!
Reply | Report as offensive | Link
Tue 30 Sep 2008 08:46
Triumph stag rover V8 Engine conversion - jc2
The small block Ford was only nine pounds heavier than the alloy block Buick which was one of the reasons Buick dropped it(and sold the patterns/moulds to Rover).
Reply | Report as offensive | Link
Sat 2 Aug 2014 13:21
Triumph stag rover V8 Engine conversion - Oz KJ

Stag has 5 main bearings - taken from Dolomite - but 2 of them are actually narrower to allow the extra conrods for the V8.

When I look at my Sprint and the Stag side by side this is evident.

All the Stag things have/can be fixed.

I bought mine in 93 and until 2000 was my only car.

It had 90,000 kms on the clock when I bought it, and now is having a new (rebuilt) engine but is showing 400,000 k's on the odometer.

From Melbourne to Perth is 3500 Kms - I did that 7 times in my Stag and always in summer - at times it was 48 degrees C - so they will do anything you want them to do.

Here (where it is hot) you need a 16 inch 20 amp elec fan, 4 core radiator, TR6 spoiler - and that's it = 130 kmh all day driving across a desert.

Timing chains should be done every 40,000 k's (I've done it about 8 times (!!!) and that has been using AE chains. I have IWIS chains that are supposed to last forever - I won't do enough miles now to find out - as I stopped doing the long distances in the Stag a while back.

The problem with the Stag having different engines is that the Triumph engine revs quite high. It has a 3.7 diff ratio which ensures this. If you put a low revving old pushrod V8 in it with staright drive (no overdrive) they can "run out of puff" - or be like driving everywhere in 3rd gear - so consider that.

They reckon they make 3.45 fr Stags - all the ones I have seen are just sedan ones - and they aren't as strong. They are similar (I did go into it when I put a 3.45 in mine as a temp option) but from vague memory pinion bearing is bigger on the Stag ones........

Reply | Report as offensive | Link