TR6 Flywheel installed without the locating dowels?

[karls59tr]

I know someone who claims that a shop had installed the gearbox on his TR6 and that the flywheel did not have any locating dowels. What affect would that have had on the clutch and gearbox?

 

[poolboy]

The 2 locating dowels for the gearbox alignment with the engine and crankshaft are supposed to be in the "rear engine plate" not the flywheel
There are 3 dowels on the flywheel to align the pressure plate to the flywheel.
As to effect of not having the dowels in either to assist alignment, I can't say other than it's important to have alignment, using dowels or not.

 

[TR3driver]

The 2 locating dowels for the gearbox alignment with the engine and crankshaft are supposed to be in the "rear engine plate" not the flywheel

And they weren't actually dowels on at least some TR6 (all I think). Instead, there are two special tight tolerance holes, and the factory used tight tolerance bolts (what they called "dowel bolts", PN 132872) in those holes.

Having the pressure plate out of line would just cause vibration, I think. More of an annoyance really, although it might shorten the life of some components around it (like the rear main and transmission input bearings).

But I suspect that having the gearbox out of alignment with the crankshaft (because someone left those bolts out or used ordinary undersize bolts in their place) is one of the causes for the infamous TR6 clutch problems; and can also cause problems inside the gearbox. The input shaft is forced to run at an angle to the other shafts, which in turn forces the center of the clutch plate to run at an angle and the clutch to drag. Might even be the reason for a weird clutch failure that several local club members have seen, where the flat metal plates that connect the friction surface to the hub break and tear.

When I got Stag #1, those bolts were missing, and it had a bad bearing between the input and mainshafts inside the gearbox. Not a common failure mode. I paid a professional to change the gearbox & clutch; he still left them out and several others besides. (That shop is long gone now.) After I fabricated and installed the dowel bolts (along with replacing the broken flywheel housing), the clutch worked better than it had since I bought the car.

No one seemed to have the right bolts for the Stag (although a few vendors sell ordinary bolts as replacements), so I bought some drill rod in the right size (3/8" IIRC) and threaded it on both ends for nuts. Another alternative might be to buy aircraft bolts with precision shanks, but I wasn't able to find them at a reasonable price.

 

[dklawson]

Or are you talking about the dowel that keys the orientation of the flywheel to the crankshaft?

If you are talking about the dowel keying the flywheel to crank, it is important if the shop also balanced the crank and flywhee/clutch components. Without the dowel you have a 1 in 4 chance that the flywheel will be put on the crank clocked wrong which will defeat the balancing. If on the other hand the crank/flywheel parts were not balanced I cannot think of any ill effects of leaving that dowel out. The shear load from engine torque would still be carried by the bolts.

 

[cheseroo]

For the gearbox to engine locating pin/bolts, I just bought dowel pins from McMaster-Carr and used 2 of those. I figured there was enough fasteners around the rest of the bellhousing to keep things together. It was more important to me to have things aligned correctly rather than worry about the remote change of the gearbox falling out.

 

[TR3driver]

rather than worry about the remote change of the gearbox falling out.

Makes sense to me.

But I was already repairing the second case of "the gearbox falling out" that I have seen on my own Triumphs, and it seems to me that the factory must have had some good reason for making the change. Those special bolts have to be more expensive even at the wholesale level, than the plain pins used on earlier Triumphs. The factory also beefed up that joint several different times, which kind of suggests that they were having problems similar to mine. Making it weaker than original just didn't seem like a wise move, to me. Besides, it was a fun lathe project.