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TRIUMPH Contents page  > Net Nuggets contents  > Installing the rear main seal on a Triumph TR3-4




Triumph TR3 FAQ page

TR2/4A Rear Crank Seal installation by: Hardy Prentice

I spent many months researching this during 25 years of racing my TR3 at the National level. I have also built quite a number of TR2/4A race and street motors. I have been a TR owner since 1961 Making the factory seal work is not difficult with a factory TR2/4A crank. The factory TR4 manual images are a useful addition the TR2/3 ones, but both factory manuals have the same CRITICAL Error. The alignment tool drawing in both factory manuals needs to be changed to 2.818" where the tool fits inside the seal. The rest of the drawings in the TR2/3 & TR4/A factory manuals will work. The tool seal and bearing surfaces must be concentric. The handle is not necessary, and thick walled tubing can be used to save cost and weight. I was given a tool made to the workshop manual(s) sizes, and the motor that I rebuilt using it leaked oil very badly running on the dyno (no G forces involved)! Previously, I had used the back end of a crank with the flywheel flange sawed off, with used main brg. shells with thin paper (or thread) inside to fill the normal bearing clearance, and .0025b to.003b feeler gauges between the seal and threaded crank surface. (If you know the seal is working OK, feel free to reuse it as is, resealing the main brg cap sides to the block recess, and avoiding any damage to the seal.)

1. Use the tool to check the seal's ID for size and roundness by holding the seal ID to the 2.818b surface of the tool. Illumination behind the seal and tool help.

2. Hand work can usually make the seal fit the tool very well, or try another seal. (I made a jig from two rear main caps to size the seals in a lathe)

3. Install the tool in the block and the rear main cap first and carefully check that the seal halves will fit in the block recess with the tool in place, and the rear brg. cap torqued. There have been seals made where the seal step OD was too big for the block/cap ID. A problem here can be fixed by a hand file or grinder applied to the seal step OD. If you omit this step, you can destroy the seal and not realize it until too late.

4. Use a small amount of silicone sealant between the seal and block where the seal flange is bolted to the back side of the block/cap. (Go to the next step Before the sealant sets.)

5. By hand, press the seal halfs evenly towards the centralizing tool, then do not further move the seal halfs when you tighten the seal set screws. Allow time for it to set. . During final assembly, also use a small amount of silicone sealant on the seal split line, but VERY thinly, so that it does NOT block the internal threads of the seal.

6 Do not hurt the seal when you lay the crank in the block.

7. follow the manual(s) carefully. The rear main cap sealing felt needs to be soaked in something like aviation permatex, short pieces at a time, and then be driven into the recess on each side. A B<b hex (Allen wrench) key works well as a driver.

8. The tool can be used to align a seal with the crank in place...Interested?

Hi Hardy, thanks for the detailed description. You wrote:
> > (I made a jig from two rear main caps to size the seals in a lathe)
Does this mean you removed material from the mating faces and then bored the seal back to round? (Kind of like line-boring an engine block)
> > 8. The tool can be used to align a seal with the crank in place...Interested?

Someone was asking that very question recently, plus I'd like to know how you do it. Please tell us. -- Randall

Hi Randall, thanks for all of your great posts!

After the one seal failure on the dyno, where the oil actually made it to the ceiling of Huffaker's dyno room (most embarrassing, although Joe was understanding) I spent a great deal of time asking many people what they knew about this kind of oil seal. No one could tell me how deep the threads in the seal needed to be, so I bored a number of seals, and they all worked with some reduced depth. In addition to dressing the split line, one can hammer on the seal face to close the ID; an old school secret from a dear departed friend.

I will soon post how to change a seal in place, but part one had to be posted first. btw: do to no fault of my own, the dyno day was on the Friday when I had to make it to Barstow, CA by Sunday night to arrive at the Atlanta ARRC in time. It was very late when I returned to SF Friday, with the TR motor where the GT6+ passenger's seat normally was (also how I drove the motor to the dyno) I had to pull the crank, as I had not yet figured out how to avoid that, install a used crank seal with the old, modified crank, and put it back together with the good crank. I then had to install the motor in the race car, pack, hook the TR3 to the back of the E Type, and drive. I was very happy when the race motor had no leak after the first track session at Road Atlanta, as that was my first chance to find out. Hardy


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