[TR] Follow-up re: "Have I ruined the flywheel on my TR3A?"

[Mo and Dave MacKay]

I received many helpful replies to my posting about my TR3A's flywheel (see
below). I thought that I should provide a summary to the list.

 

In a nutshell, the centre hole in the TR3A's flywheel (that the nose of the
gearbox's input shaft goes through) was too small to fit on the machinist's
balancing equipment. So he made it bigger by about a half an inch so that it
would fit on his machine. He then balanced the unit and gave it back to me.
The machinist thought that enlarging the hole was no big deal since the
pilot bearings (of modern cars) are held in place in the crankshaft by an
interference fit.

 

The advice I got from list members is that it is, in fact, a big deal. The
hole in a TR3A's flywheel is sized to be smaller than the pilot bearing
(actually a bronze bushing) so that the pilot bearing can't move past the
flywheel towards the transmission. Now that the hole has been enlarged it's
too big to do that. 

 

In general, the feedback was that my flywheel was spoiled, and that I should
replace it. However, a few workarounds were suggested:

   - milling a shoulder onto the flywheel and then machining a custom pilot
bearing that would fit into that shoulder

   - machine and affix a spacer (like a washer) for the flywheel to return
the hole to its original size

   - cut another bushing (or make a new, longer pilot bearing) to "take up
the slack" between the pilot bearing and the end of the transmission's input
shaft

   - use a TR6 flywheel and ring gear (with the bevel flipped) instead

 

I ended up expanding the pilot bearing (by dimpling it with a punch) and
hammering it carefully into the crankshaft. I'm relying on an interference
fit keeping it in place. I recognize that this isn't a good long-term fix. 

 

I'm now on the hunt for a TR3A flywheel (there are 3 different types for the
4 cylinder TRs). I need the kind used by TR3A (post 50,000), TR3B, and TR4
(not TR4A); it has a bolt on ring gear and is used with the later starter
and a spring-type clutch cover. After get a suitable flywheel, I'll
eliminate the bodge. 

 

Thanks for the advice and assistance.

 

Dave MacKay

TR3A s/n 68639L

near Toronto, Canada

 

>I'm replacing the gearbox in my TR3A with a Toyota W58 transmission, using
the HVDA conversion kit. The HVDA kit requires that one use a TR6 (Borg &
Beck) pressure plate >instead of the usual TR3A pressure plate. The TR6
pressure plate doesn't fit into the holes used by the TR3A pressure plate;
new mounting and dowel holes must be drilled. 

> 

>I took my old flywheel along with the new pressure plate etc. down to a
machinist to have him:

>   1) true the flywheel 

>   2) drill new holes and mount the new pressure plate to the flywheel

>   3) balance the resulting unit

>Everything went well until step #3.

> 

>The centre hole in the flywheel (the one that the gearbox's input shaft
goes through) was too small to fit on the machinist's balancing equipment.
So he made it bigger by about a half >an inch so that it would fit on his
machine. He then balanced the unit and gave it back to me.

> 

>Has enlarging the centre hole ruined the flywheel? Or is it no big deal (as
the machinist claims)? If it is a problem, and since the flywheels are NLA,
how could I fix this?