Swaggie
SubscriberNO. I thought I was clear but my English must be deteriorating.What about the late 4.0 crank in the early 3.9 block.
BTW there is another problem I just thought of. The 3.9 block does not have a crank sensor mount ( hole in LH rear flange), or provision for a cam sensor or provision (bosses and threaded holes) for knock sensors.
All of these are necessary for Thor Motronic to work.
Regards Philip A
Master
Originally Posted by p38arover
Okay, I'm doing this conversion very soon. - I Have a late model 3.9 but putting the earlier v belt timing case on it. Do you have any pics at all? Do you know the correct length of the spacer if you use the old crankshaft Pulley? I haven't removed the timing covers yet to investigate all this so forgive me for the questions.
cheers
Swaggie
SubscriberInterim 3.9 (jan1994 onwards) has the same length nose on the crankshaft as vbelt.
Only the keyway is longer , so no problem.
This assumes you are actually talking a late 3.9 and not a 4.0.
Regards Philip A
Master
So I think I have this straight now, maybe.
I can put a 4.6 crank in my 4.0 with 4.6 pistons and rods but I cant put my 4.0 crank in into the 3.9 so that I could use the 4.0 accessories.
James
Swaggie
SubscriberAbsorutery correct.So I think I have this straight now, maybe.
I can put a 4.6 crank in my 4.0 with 4.6 pistons and rods but I cant put my 4.0 crank in into the 3.9 so that I could use the 4.0 accessories.
James
But beware that 4.0 engine blocks can be a lower "grade" than 4.6 and be more prone to liner slippage. I recommend top hat liners if you do that.
Regards Philip A
TopicToaster
Cutting down the mains to smaller size will reduce oil shear and improve stability of the film layer. Can anyone say if the 4.0/4.6 big ends are larger than a small block chev? If so good things can happen, verry good things indeed.
Offset grind the crank and use the offset to reduce to SBC and you have hundreds of rod options, BUT, use the offset to destroke engine so reduces rod angles (reduces forces acting on sleeves, yay (not that it's a solution)). Use the new sleeves to regain capacity and makes the engine more square (more revs). I could go on but in a nutshell, you can obtain 5 figure rpm's from std bits.
Master
Why do you need revs in a 2 t vehicle. Might be good for trans plant into a Midget or MGB though.
Last edited by JBM770; 19th April 2011 at 09:43 PM. Reason: typo
TopicToaster
Just thinking out loud, have done it previously, been able to sustain 18K on only new pistons/rods. Could work this out toget some good low down torque instead and make it strong plus make replacement parts cheap.
Master
There are plenty of strong parts made for Chevs so I know what you mean.
For 4WD extra stroke would be a good thing.
TopicToaster
Yes, instead of shortening the stroke to speed things up, offset grind the other way and gain stroke length and take the big end size down to SBC. Nitriding, shot peening etc take care of the metal post machining work.
Make some shorter pistons to try to minimise increasing rod angles (reduces friction and loads). We need to find a piston from another source to suit the bore, or within oversize abilities of sleeves but assuming that we top hat that won't be an issue, with a shorter skirt and raised pin height. Hopefully it's a standard product piston that's made by a aftermarket supplier, so we can just change the crown to suit if required.
A SBC rod that suits the required length and pin size (and profile that clears any interference areas on the block). And finally get the bearings plasma sprayed, a cheap proceedure that produces amazing results. I've personally seen bearings from a NASCAR engine that threw a oil pump belt and ran 3 laps with zero oil pressure and replaced belt, finished race and when stripped if it was a road car you'd reuse them.
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