12-01-2020, 02:04 AM
A Modern Lip Seal for the 1 1/8” crank A7 Engine
*PART 1
The problem: The rear main bearing seal on the early 1 1/8” is felt which may slow down the seepage of engine oil but is still not oil tight allowing oil into the flywheel housing portion of the crankcase which can affect the clutch with undesirable consequences.
The solution: design and make an adaptor plate that bolts on the back of the rear crank case bearing housing (BB10) which holds a lip seal to prevent the leaking in place of the standard large felt ring and plate (BB6) . Currently it would seem that there is not an adaptor plate being made for this crank size.
Considerations in design: There is minimal space behind the bearing and the face of the flywheel and a short boss on the flywheel that the felt seal would seal on. The new seal would have to be positioned so that the seal lip would make contact on the flywheel boss such that a proper seal is made.
Choice of seal: There are a lot of modern lip seals but the application required that the seal deals with heat, hot oil, and low to high RPMs. The seal needed to seal on the flywheel boss and the inside of the rear crank case bearing housing (BB10). Since the odds of finding an automotive seal that would meet both of these requirements was virtually nil, I set out to find one that fit the flywheel as this was the primary focus for meeting the criteria for oil tightness. I work at a garage specializing in servicing and restoring British Sports Cars (MGs, Jags, Triumphs, Lotus, Minis etc.) and we keep a very well stocked inventory of spares. I looked at all of the seals we had and found a couple that fit the flywheel perfectly. The best one was a MG transmission output / driveshaft seal Part number CAN 224 which is a common and easy to obtain seal as it fits a number of different cars. It has to deal with heat, hot oil, and high RPMs which is exactly what I wanted. The only concern I had was its thickness which was about ½” so I would have to see if it could be positioned to fit all of the required dimensions. The flywheel requires a SPEEDY SLEEVE to be pressed on to the boss on which the seal will run to insure a good smooth surface for the seal to seal on without having its lip worn off.
2 SPEEDY SLEEVE .jpg (Size: 60.96 KB / Downloads: 178)
Can I make it all fit ? : The next problem was seeing if it could all be made to fit. My solution was to make a scale drawing twice the size of the components when assembled to see what issues I had to deal with. Everything was measured and drawn on ¼”square graph paper. It soon became apparent that the seal could be used and would fit in the space I had for the seal and its retainer with enough clearance that there would not be any issues. The biggest concern was that the position of the seal would be close enough to the flywheel that the actual lip of the seal would be positioned properly on the boss that does the sealing - or did when the felt seal was used.
3 DRAWING FOR FORUM ARTICLE.jpg (Size: 42.75 KB / Downloads: 177)
Trial fitting: I needed to put the bearing into the housing and install it on the crankshaft so that I could place the seal between the bearing and the flywheel and actually see that my drawing and calculations were correct before machining the seal holder. I didn’t want to have to press the bearing into place as this was something I didn’t fancy doing more than necessary for all the known reasons. I needed to make a bearing stand-in or dummy bearing machined to the same width as the real bearing but with a sliding fit on the “crank and in the holder. Since the “stand in” was pretty thick and large I didn’t have any metal or plastic I could sacrifice just for this job and I didn’t think wood was suitable for a variety of reasons. So I made one from a material that you may not think would be possible…. Lightweight Auto body filler! I’ve used this before for a number of corrupted applications with great success. Once properly hardened it can be machined, tapped, drilled, sanded and even polished to a high gloss!
To make the blank I coated the inside of the bearing housing (BB10) with Vaseline so the filler would not stick and put it flange side down on wax paper. Sufficient filler was mixed with the hardener and was dispensed into the housing opening trying not to create too many air bubbles. Once hard the blank was popped out and cleaned up ready for machining. The blank was sanded dead flat on the wax paper side and chucked in the lathe. The blank was faced to give the same width as the bearing and bored out to 1 1/8”. This now gave me a depth gauge to use to determine the position of the oil seal in the holder.
4 BEARING SUBSTITUTE .jpg (Size: 70.08 KB / Downloads: 177)
4A BEARING SUBSTITUTE (1).jpg (Size: 30.41 KB / Downloads: 176)
4B BEARING HOLDER WITH REAL AND FAKE BEARING.JPG (Size: 61.98 KB / Downloads: 177)
TO BE CONTINUED IN PART TWO