Engine and Transmission Tech

Hi,

Does anyone know what the optimal engine angle for a Buick 3.5L or Rover 4.0L should be? Currently the back end of the engine is lower than the front of the engine as determined using a level (compared to true level). I don't know the angle in degrees but it probably is less that 5 degrees which equates to about a 3/4 inch drop when the level (true level) and engine level line are extended to the back fire wall and marked with a pencil. I assume I should keep the engine as level as possible (while driving....i.e. using correct suspension and rake and not a hand held level to fix the comparator plane) which I can accomplish through using a combination of 1). slotting the engine mounts (lowers/tilts engine 1/2 an inch), 2) rasing the trans (1/4 inch spacer in trans mount) and 3) positioning the JAG IRS up or down a 1/2 inch or so. Of course all of this needs to take into account ride height (e.g. rear end) and some clearence issues. I think I will fix the rear end as high as possible into the car (low ride height while retaining 1/2 shafts parrallel with ground). Any thoughts?

Neil

Neil, about the best you can do is going to be 3 degrees on the engine with the crank as low as you can get it in the front without denting the pan when the engine moves, and the tranny tailshaft a reasonable distance above the crossmember. This is good, it is a very typical driveline angle for this type of car. Your Jag IRS is most likely going to match that angle fairly easily, depending on how you have it mounted, but the JAG halfshafts will typically be angled down a degree or two towards the wheels at normal ride height. A bit more won't hurt anything. This will be consistent with mounting the differential high and should give proper suspension travel.

Jim

Hi JIm,

Thanks for the thoughts... I feel like I should be able to get it close.

Neil

Neil, don't guess on the engine angle, for best results the rear pinion angle should match so the drive shaft will be in phase and balance easier. You can get an inexpensive angle guage from Harbor Freight ($4) or most hardware stores with a magnetic base. Just attach it to the pinion flange and get the reading and then match your engine angle to that, or start with the engine and match the pinion to it.
I find the best place to check the engine angle is on the transmission output shaft, it's a known true 90 degree face to the crankshaft centerline. The crank centerline and the pinion centerline need to be parallel, but not inline for best driveshaft alignment. They can be offset both horizontally and vertically a bit and you get better wear on the u-joints if they are.
Most engines are not installed level originally anyway, usually the transmission end is lower than the front, that's the reason most intake manifolds for carburators are milled at an angle, so the carb will be level. Most wind up between 3 to 7 degrees as I remember.

Another option is to put the car on jackstands and adjust so either the pinion flange or the milled flat on the front of one head is vertical, zeroed out with a level and then adjust the other to match. Not much chance for error that way.

Jim

Jim and Bill

Thanks again. More good advice. I'm playing around a little more with the JAG IRS position and after reading the MGB RoadMaster pages a few extra thoughts have come to mind which I'll probably ask about once I learn a little more.

Neil

I've always wondered about this. It seems like the angle was pretty extreme. It looks like 5º or something on the carb flange stock. Anybody know why?? It seems like that would make trying to setup driveline angle a lot more difficult. I dropped the engine about 1.5ish inches and that gave me some latitude to get the engine more around the 2º-3º but I couldn't level it. I will not be able to zero out the pinion angle because of this. Strange.