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okay I have a problem. newly rebuilt 1128 4 sync box with 927 laygear. 3 sync clutch housing std drop gears. all bearings and syncros replaced, properly shimmed, box looks perfect!! Box whines at idle in neutral. Box also very loud whine while driving in all gears. Pulled engine and removed clutch housing, everything looks fine. Did notice the primary gear has more play side to side ( running clearance on crankshaft tail).

what causes excessive gear whine, could primary rear bushing slop cause this? maybe using a 3sync clutch housing on a 4 sycn box? thanks

Very difficult to diagnose noises long distance. But excessive primary gear wear will cause some whine, the more there is the louder it is. If I remember rightly the primary gear should have about 8 thou end float.

Other things worth checking are idler gear play / end float, first motion bearing, diff pre load & fitting as well as checking the crown wheel & pinion are a matched set.

I have run many 3 / 4 sync combos, so this should not cause a problem as long as you have used the correct idler gear bearings.

There's a bit of food for thought, I am sure there will be other people chipping in soon.

M

A common source of that whine is when the bearings and / or bushes get worn and the gears become slightly cocked, the teeth then no long have full contact across the tooth face, but on the tips on either side of the teeth. If they have been running like this for a while, they will wear like that and then new gears along with the bearings would be in order.

That what you are reporting happens in all gears, even neutral, suggests to me that it would be in the drop gears. Certainly if the Primary Gear bushes become worn, it can cause them to become noisy. Also check the the dowels between the gearbox and the transfer (clutch) housing are there and reasonably tight.

As far as I can see the only thing that looks bad is it the primary gear bushings are worn out, you can make it rattle on the tail side to side. I guess this could have made it hard to check the primary end float properly. The thing is, it was really loud. Should std. drop gears make a sound at all? The drop set is a miss match set but all are so nice looking. Can one check end float with 1 feeler gauge or will it always be off?. thanks

A worn primary gear bush will cause the rattle you describe. Fit new bushes, ream them to size then set the end float to 8 thou.

http://www.minispares.com/search/classi ... 0bush.aspx

Mark F

Rattle when cleaned and dry fit. Wasn't sure if the oversized primary gear bushings could cause this whine.
Side to side slop of probably 20 thou, I'll check in the morning.

20 thou end float (side to side) is MASSIVE!

We used to use 10 thou on the racers.

M

I mean primary inside diameter compared to tail, like primary bushings too big

its more likely to be the idler gear bearings that are worn if the drops are whining then in neutral as it can cockle over far more than the primary - primarys will make the annoying chatter when they are worn, but the clutch disc helps to hold it parallel on the crank


whining in drive can be the first motion cockling over when power is going through it.

All bearings are new with 60 miles on them purchased from mini spares

Speedwell Sprint wrote:All bearings are new with 60 miles on them purchased from mini spares

they can be damaged fitting them though.........


I have just seen this happen when a customer caught the outer cage with a punch and didn't realise, the idler rotated fine, but the bearings couldn't move and broke up in a couple of hundred miles

From my Haynes...

Primary Gear Endfloat : 0.0035" to 0.0065"
Idler Endfloat : 0.003" to 0.008"

Vizard et al:
For race engines go for about top limit.

My top tip:
Those thicker idler shims are expensive, but if you have access
to a milling machine you have another option...

You can close up the idler endfloat by machining a few thou off the
gasket face of the transmission face. Probably a good idea to
machine the other face by a few thou first to ensure that it is flat
and sits nicely on the machine when the gasket side is done.

NB: Just check that there is plenty of clearance for the "nose"
on the first motion shaft and the screws for the oil pump.
... and write down how much you took off for future reference.

If you have plenty of old shims available, you could even machine
the case slightly more than required. Put your old standard shims
on the mag-chuck of a surface grinder and make a selection of shims
of different thicknesses. The possibilities are almost endless...

I measure the thickness all the transmission gaskets I use and
have found that the standard type red gaskets are normally 0.031".
I bought one from MiniSport once that was about 0.010" thicker...
They must consider a tolerance of +/- 33% to be an acceptable
engineering tolerance.



Another idea:
The transmission case is dowelled to the gearbox to keep
the bearing [EDIT "bearingS", the one for the idler AND the
one for the first motion shaft /EDIT], in the 'box and the
bearing in the case aligned.
Sometimes if these are NOT inline, the transmission case
may need to be bored offset and a sleeve put in to correct it.
You really need engineering measuring gauges to check this
properly.

If bits are mixed and matched, like they are for most of us,
it could be just a set of adverse tolerances that are the problem
here.

You say you're using 3 synchro drop gears on a 1128 box, so you have an idler gear with a short pin on both sides.

It should be running like this:



How is your box side idler bearing?

4sync idler gear with one side longer

Speedwell Sprint wrote:I mean primary inside diameter compared to tail, like primary bushings too big

I'm very reluctant to suggest this, but reading the above, reminds me of the days of my youth when I mistakenly fitted a 1275 primary gear to an 850 crank. That whined (until the centre broke out of the clutch plate!) then it went quiet I was not popular that day