Diff <-> Engine alignment/height

[Eternal]

Hay all! Today i put the engine into the chassis. All i can say is..... what a bugger!
I went to kneel down and knelt on a roof felt tack.... ouch. Anyhow i have a few problems i would like to talk to you lot about. First the eye candy.






Only 4 pics per post so the next post has my questions.

[Eternal]

OK i got the engine crank and gearbox to dead center that was quite easy.
The problem im having is getting the diff and gearbox to line up. Im 15mm out but that left 50mm of sump under the chassis rails. I could get the cast ally sump cut down but its winged and would cost a fortune to get done. Also have a steel sump but that needs baffles and all kinds being done to it (same height as ally sump).

My question is this... what is the max drop that is allowed from the engine to the diff? As if i can raise the engine a little more that would solve all the problems. Also the top of the engine is 200mm above the top chassis rails so thats ok the hood im going to make will have a bulge so can go higher if needed. Any advice more than welcome!

[flyerncle]

I personally put the engine/box as far back as possible for balance,put some blocks under the front and rear of the chassis at 4ins front and 5 1/2 rear and this wil give you some idea of a good working height with all four corners set at running height.

Propshafts are designed to run at differing angles to account for the likes of live axle travel so slightly out of line should not matter too much.

[mark]

In my opinion 15mm difference in height wouldn't be a problem, apparently having them dead straight causes brinelling (not sure on spelling!) which causes joints on the prop to wear out faster

If you picture a heavy goods vehicle prop they are always on an angle

As to how much of an angle you can run with a short prop on a roadster i'm unsure, but a phone call to dunning and fairbank will give you a good idea

Your sump is a touch lower than i would personally like but your choice of 18" wheels will help with this a little

As with most things its a balancing act, engine height, prop angle and ground clearance will all end up being a slight compromise by the looks of it, nothing that should cause any major probs though

A sump mod may cost you and cause you hassle, but do it right now or it will bug you until you do! then you wont have to make any compromises!

[Eternal]

Also the gearbox bell housing is about 40mm below the chassis. and this really bugs me as there is nothing i can do about that. in an ideal world i would like to do a sump mod on the steel sump and also raise the engine another 10-15mm lol but that would give 30mm height between diff and tranny

[mark]

Maybe 30mm would be ok, ring a prop manufacturer to find out

[Eternal]

Ok measured the length i would need in its current position.

Using UJ's that are 40mm from the face of the diff and gearbox the shaft would need to be about 500mm from center of UJ to center.
This would give a drive shaft angle of 1.72° over 500mm going 15mm heigh
Idealy i would like to be 500mm going 30mm high that gives 3.43°.

[flyerncle]

Personal note again,if you mod the sump add wings to the side's to add capacity lost through shortening and if you intend hard driving/track use baffles are essential to stop the oil splashing around too much as it will cause problems in the breather system and removing the guts of the pcv valve helps,use a catch tank with a filter.

[Eternal]

Yeah the skyline sumps steel and ally have quite good baffles as standard. But the GTR pickup i have wont work will the steel sump so will have to a lot of modding to get everything to fit ok. Will have to cut out the steel sump baffles and try and fit the ally ones in. Humm will be fun......

[les g]

Sorry for being a bit nerdy but i know the answer to this one
a standard propshaft uj,s normally accepted working angle is 15 degrees
so a propshaft with two joints is normally recommended to work at up to 30 degrees.
so your 30mm offset is well within nomally accepted limits.

There are specials that allow more angle at extra low revs but then torque
starts doing massively strange things and extra large support bearings are needed and then it gets really extra nerdy..

but the simple answer is 30degrees in a car drivetrain is normally acceptable
cheers les g
seem to remember there is a variable somewhere that the maximum angle decreases as maximum revs increase ,but too throw in a googly i seem to remember that lifespan and rating of a joint is based on a continuous rpm figure