GMC V8 Diesel Range Rover issues

[a30racer]

I have recently taken the plunge & purchased a 1981 2-door Range Rover fitted with a 5.7 Litre GMC V8 Diesel engine. After some messing about, we determined that the engine had been hydraulic'd and was distictly unwell, so I purchased a 6.2 Litre V8 Diesel thinking that they would be a straight swap. Mistake!!
Both engines have adaptor plates (5.7 was fitted to original LT95 manual 4-speed and the 6.2 came with ZF auto box) but there are some issues (starters are on opposite sides and engine mounts are very different). My question to the forum learned people is this :
I plan to use the 6.2 Litre engine, mated to the LT95 (as I hate autos) with the auto flex-plate (to take care of the starter) and then have a flywheel made that bolts on over the flex-plate to basically mount the clutch assembly to and obviously dampen out the big diesel pulses when its (hopefully) running. Does anyone know who could make me such a bespoke flywheel and also if there are any issues in having it bolted over the flex-plate? Thanks for reading this far!

[welshpug]

will the 5.7 flywheel not fit the 6.2?

if you have a flywheel made, you wouldn't need the flex plate.

[a30racer]

I had thought that the 5.7 flywheel would fit, but sadly it is slightly smaller & the bolt pattern on the crank is different too. There is the added complication that these wierd American engines use external balancing (offset weights on front pully and flexplate) and I don't understand enough of the science of that to do it with any confidence. My thinking was that I could use the flexplate to do the starter and balancing stuff and then just have a simple lump of a flywheel bolted over that to bolt the clutch onto.
Thanks for your input anyway.

[dodgerover]

This doesn't help but back when these were a reasonably popular conversion they used to have a reputation for breaking diffs and gearboxes when coupled up to a manual box hence the reason most are autos.

[composimmonite]

Have you considered selling the 6.2 and using proceeds to rebuild the 5.7 ? Problem solved

[squonk]

Aug 19, 2015 20:29:02 GMT dodgerover said:

This doesn't help but back when these were a reasonably popular conversion they used to have a reputation for breaking diffs and gearboxes when coupled up to a manual box hence the reason most are autos.

Yes, and the ZF wasn't really up to it either - the better match was the Chrysler three speed from the earlier Range Rover autos. Unfortunately those American V8's are not brilliant engines. They have masses of torque at low revs (which is why they destroy transmissions) but very little power and a low rev limit. They are too heavy to be much use off road where the torque would be useful as in any kind of soft material the weight causes the front end to bury itself. If you want to tow three tonnes at a low speed they are ideal but in reality a Range Rover fitted with either a 200TDi or a 300TDi with a fuel pump mod is a far better and more usable vehicle. Perhaps you could sell both engines and buy a rusty Discovery diesel as an engine/transmission donor? Or do you have a specific need for the V8?

Seeing as the vehicle is an original two door with this engine fitted to it and knowing how rare and desirable two doors have now become, if it were mine I'd be restoring it back to it's original state as it would be quite a valuable vehicle in standard form. A fully restored original two door can fetch £10k+ these days, early ones double that.

Have a look at some of the comments on the lr4x4 forum about these diesels:

forums.lr4x4.com/index.php?showtopic=3470

[colnerov]

Hi, I had a 6.2 in my Range Rover but I was running the ZF and had no problems with the transmission. But I did at one stage have the engine in my series LR which was running a Jag model 12 auto but I had trouble with the vacuum feed to control the box but that is another story. The point of saying that is I had to make up a crank adaptor for that so I can see where you're coming from.

A crank adaptor for yours would need to be double drilled, one set of holes to bolt up to GMC crank sandwiching the flex plate as you suggest, another set of holes to bolt up a RR flywheel to take a 10" RR clutch. The crank adaptor thickness was if I remember correctly just over 1" thick but you will have to check that for yourself by a bit of careful measuring. It shouldn't be a long way away from the thickness of the bellhousing adaptor. Don't get deceived by the ZF crank adaptor as the ZF bellhousing is quite a bit deeper than the LT95.

Good luck.

Colin

P.S. If I think of anything else I will repost or any more questions ask away.

[deaddave72]

The challenge with the 5.7 is that its not that common and only really common in the Oldsmobile cutlass for a time (from memory) having just checked my favourite US spares web site RockAuto.com they do list quite a few engine spares though. The 6.2 and 6.5 were fitted to loads more vehicles and parts are readily available from the states,not to mention a bit more economical. The LT95 will handle the power and torque so long as no sharp clutch operations happen, an auto is by an far the better option, as would fitting a salisbury rear axle tbh. However that is more hassle,depending on your view point.

I will concur with squonk with the 200 or 300 tdi disco donor and swap bits route, its still a 100" wheel base and you will have several spares as well as some bits to sell off to fund the swap. It does keep it all landrover and will will retain a degree of value upon completion due to that.

I have driven an early 110 with the 6.5L option on the LT95 and it was quite spritely tbh. The engines do rev really high and you will curse word yourself on how high they rev.


If you really wanted a big ass diesel 4x4 , then getting a GMC truck will be a better option, spares are not an issue as they are plentiful.

I'm currently throwing a 7.3L V8 Ford diesel in my Cadillac limo

[vitesseefi]

Did email you Tuesday, but may be confused about which address still works so just in case......

Can't remember whether you counted 129 or 139 teeth, but 139 seems fairly common.
See links
www.pirate4x4.com/forum/tow-rigs-trailers/394373-gm-6-2-diesel-flywheel.html
www.shoppersworld.com/category.php?categoryId=2196&t=2658&x=450&sk=&so=&vt=list&
shop.advanceautoparts.com/p/perfection-clutch-new-flywheel-50-2710/15260103-P?navigationPath=L1*14925%7CL2*15053#fragment-2
www.rockauto.co.uk/catalog/raframecatalog.php?ck[ID]=0&ck[idlist]=0&ck[viewcurrency]=GBP&ck[PHP_SESSION_ID]=e9vdbi9cp4pukrtd0id1ug5i24


Not necessarily the right ones, but just showing that they are out there and cheap (though shipping likely not!)

Note the external balance issue which probably rules out getting one made. Best buy one and get it drilled for LR clutch if necessary……..

Nick

[hario]

I suppose you need the flex disk for the starter ring gear?

Perhaps you could get a shop to turn down an LR flywheel which suits the gearbox to allow the clutch to bolt up, but then you would also have to commission an adapter puck to bolt between GMC crank bolt pattern and LR flywheel bolt pattern, much like the gaz fab guy does for his Mercedes to LR conversions, like so in fact:

www.gaz-fab.co.uk/node/23

[a30racer]

Progress has been slow, but some movement has happened recently. Gearbox has been removed and now rebuilt. The overdrive casing had split (which prompted the removal) and a tooth had been broken off the reverse idler and another off the low range in the transfer box , which leads me to think the previous owner had tried to free off the seized engine by bumping it in low reverse. Pure genius!
All now sorted and ready to go back in. Overdrive will not be used again and we're now on the 1:1 of the 4 speed with highest transfer gears available. If gearing is still too low, it may be the 2.8:1 doffs from KAM may be needed. Looks like a mix of GM clutch & Rover clutch plate, which I hope to re-use, as it all looks pretty much unused. Now I know the gearbox is ok, next step is getting the flywheel sorted out and the engine/ box re -inserted.