Lots of 'Gotchas' !
Both are the same size, bore and stroke. Rover called the 3.9 the 4.0 but it was the same.
The 3.9 GEMS engine is almost identical mechanically to the THOR, BUT has a different camshaft gear and flywheel pickup location. We have found out that our Disco 4.0 THOR has a GEMS camshaft gear, so we have to strip the front end and change the gear.
If you lay two short motors side by side, one a GEMS and one a THOR, the only difference you will see is the flywheel pickup location, and you'd need a ruler to see the difference. The ring of drilled holes in the back of the flywheel is on a different PCD to the THOR engine.
The camshaft gears are visually different, the GEMS engine has four slots, three short and one long, all curved rectangular shape. The THOR camshaft gear has irregular shaped holes in addition to the regular slots. Pictures below, THOR gearwheel picture courtesy of Barri in the USA..
The Injection system is obviously different.
Peter
Both are the same size, bore and stroke. Rover called the 3.9 the 4.0 but it was the same.
The 3.9 GEMS engine is almost identical mechanically to the THOR, BUT has a different camshaft gear and flywheel pickup location. We have found out that our Disco 4.0 THOR has a GEMS camshaft gear, so we have to strip the front end and change the gear.
If you lay two short motors side by side, one a GEMS and one a THOR, the only difference you will see is the flywheel pickup location, and you'd need a ruler to see the difference. The ring of drilled holes in the back of the flywheel is on a different PCD to the THOR engine.
The camshaft gears are visually different, the GEMS engine has four slots, three short and one long, all curved rectangular shape. The THOR camshaft gear has irregular shaped holes in addition to the regular slots. Pictures below, THOR gearwheel picture courtesy of Barri in the USA..
The Injection system is obviously different.
Peter
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Beast o Bodmin
Banned
the 4.0 bottom end is beefed up.
So was the 4.6 that we took out, assuming that you mean the cross-bolted mains?
Peter
Beast o Bodmin
Banned
yep.
According to everything I have read, and we did a lot of reading before we did our engine rebuild, the 3.9 and the 4.0 are the same engine size.
Changes to the bottom end were made sometime in the late 1990's which produced the 'cross-bolted' block, where bolts were put into the main bearing caps through the lower block area to stiffen up the bearings.
I have seen both a 4.6 and a 4.0 with such a block, and have pictures of each, we own the 4.0.
The larger 4.6 was achieved by increasing the stroke of the crankshaft, the bore remained the same as there were casting issues with going bigger on the bore/cast-in liner.
Peter
Changes to the bottom end were made sometime in the late 1990's which produced the 'cross-bolted' block, where bolts were put into the main bearing caps through the lower block area to stiffen up the bearings.
I have seen both a 4.6 and a 4.0 with such a block, and have pictures of each, we own the 4.0.
The larger 4.6 was achieved by increasing the stroke of the crankshaft, the bore remained the same as there were casting issues with going bigger on the bore/cast-in liner.
Peter
Beast o Bodmin
Banned
I have a 4.0 built by dunsfold.its on twin su and is ported cross bolted block and fookin shifts.
it is based on a morgan +8 block and is so well ballanced its un real.
it is based on a morgan +8 block and is so well ballanced its un real.
Beast o Bodmin
Banned
it was in my 2 door on a manual.
Beast o Bodmin
Banned
used to eat most stuff to 90.
Beast o Bodmin
Banned
boy o boy did it shift.when i think.i drove from colchester and on the m5 raced a 08 plate vouge he finally caught me when i backed off at 100.
fookin windows nearly fell out.....
fookin windows nearly fell out.....
The 3.9 GEMS camshaft gear and flywheel sensor are different to the THOR engine's parts.
The heads are the same, should be 10-bolt type.
The GEMS flywheel sensor hole is a different size to the THOR hole and is in a slightly different position.
As far as I know, the camshaft sensors are the same, but I'll stand to be corrected on that. I'll have a look on Microcat tonight. ERR6169 is what I have, and that is for the THOR engine on the Disco 2 and P38 Rangie.
Once you get to the 3.9 engine, it is really a choice of GEMS or THOR, and the electrickery is so different that you really need to go with the one that suits your vehicle, rather than your preferences.
Peter
