Primary gear floating front bush oil leak?

[panda911]

Good morning.
I have previously posted on different subjects and have recieved good advice.
When my 1071 was being built I bought a new floating front bush primary gear from MS in Poppleton and it
was fitted.
From the getgo it leaked with a very timy amount of oil dripping from out of the hole where the split pin protrudes in the bottom
of the drop gear casing and I wondered whether oil was finding its way under the bronze bushes.
I replaced the primary gear oil seal for second time but the slight leak persisted. Fifteen hundred miles only.
The oil seal on the primary gear seems perfect.
There is evidence of oil on one side of the clutch plate only, oil also comes from the vacinity of the starter motor bolts showing as a thin film.
When building I measured the end float on the primary at 2/3 thou.
The crankshaft diameter. under the floating bush, is 1.4995"
Also read much correspondance on this website.
The only slight evidence to this is a pumping theory as on stripdown the axial float was just in excess of 8thou.
Could the tilt (pitch) of the primary gear have a very slight pumping action end to end to move oil and would a fixed bearing
primary gear carefully machined be a better way of moving forward.
Also wondering about a breather in the top of the drop gear casing, the other breather is on the tappet cover.
I am using a belt drive.
Thanks in advance for your comments.
BR
P

[imack]

I keep getting exactly the same issue with my minispares floating bushed primary gear.

[panda911]

Hello imack
Last Thursday when we knew we had a problem we called in to see Keith Calver and when leaving he just said
that he would rebuild the engine.
We picked up the 1071 and the 1290 and took them to his work shop yesteday.
I know that he tests his important racing engines (not ours) on a dyno so asked him if he
would check ours.
If it is of any interest I will post.
BR
P

[imack]

Always keen to learn panda911.
Interestingly, last year I saw an FIA race mini with exactly the same leak with oil contaminated with clutch dust coming from between the starter motor and transfer case (and ultimately from the jiggle pin) that mine suffers.

[imack]

My cars now done 200 hard driven road miles since I last replaced the floating primary gear bush. I've just removed the starter motor to see if any oil is being centrifuged from the back of the flywheel and it's currently still dry. In my experience, the clearance on the minispares floating bush primary gears tends to be on the upper end of their recommended clearance. I've got several new bushes and all the clearances vary slightly between them and they won't give clearances at the tighter end of the scale. I ended up fitting a used bush from my previous primary gear as it gave a 0.0005 to 0.001 thou tighter clearance than any of my new bushes. I've now got a total clearance of 0.0045 thou (clearance between the gear and bush & bush and crank? I think the rear bush was at 0.0045 thou as well, but I didn't make a note of it.
I always knock the box into neutral when stationary as I'm aware of issues with the modern bronze bushes seizing to the crank tail, which is probably why minispares machine the bush clearances on the large side.

[360gts]

Sometimes I scratch my head at the advancements on 'new' bits for these cars.
My point is this....I have owned and raced/rallied minis for longer than I want to remember. I have never had an issue with oil leaking past the conventional primary gears.
We come along with this new floating gear and now we have issues with oil leakage.. Maybe I was just lucky....or maybe, we are over engineering something that wasn't broken in the first place!
My thinking has always been...if it isn't broken...don't fix it.
Just my humble opinion.

[Spider]

As the clearances here increase, your crankcase breathers and their type and set up become more and more important. Venting to a catch tank won't cut the mustard, especially if it's a bigger oversized bore (1380 etc).

These hard bushing materials like that used in the floating bush need to be run on a tuftrided or nitrided crank or at some point, they'll each the crank tail (& possibly the gear too) and even then, because of their very high expansion rate, additional clearance needs to be run, but that's the cat chasing it's tail as the higher clearances increase the temperature they run at.

The only upside I can see with these floating bushes is they are a cheap approach to re-bushing the primary gear, since (supposedly) they don't need machining to fit them up. BMC looked at and tested many materials, including the Silicon Bronze that these are made from, and at that end of the Gear they found a Copper Bronze Bushing with a steel backing would support the load and require little lubrication. As Dermot has touched on, why do these guys think this will work now when it didn't in the early 60's ? I am yet to see one of these new bushes 'go the distance' like the (well proven) original bushings did.

The rear bush is in a worse position here as it (should) run 100% dry. Deva that BMC found, seems the only viable material to use here (in the right grade).

The following pics are all from different engines showing what you can expect to see and these are not the only ones I've seen, I have had loads here for 'repair';-

[Catmint]

Kieth does ahve a couple of articles on primary gears that may be of interest

https://www.calverst.com/technical-info ... placement/

https://www.calverst.com/technical-info ... -problems/

[panda911]

Thank you for the replies.
Both my cranks are EN40b metal and whilst I havn't measured the 1275 crank I will.
I agree if it aint broke don't fix it, but I did try to buy a fixed bush primary gear at the same time
as the new bushes for my floating bush primary , I was told that they are no longer sold.
It concerns me a little that these front bushes can be so variable,
I dont want oil going through the bushes on a new build engine where the wear
on a EN40 nose crank is no more than a half a thou.
I should not have to measure the diameter of every front bush.
When I was a kid you may remember that the CV ball bearings in the back of front hub joint itself were available
oversize, several oversizes.
Seems to me the nose on the crank is only going to get smaller not bigger, if BL were thoughtful enough to
provide oversize balls for the CV joint then we ought to be able to buy oversize bushes for slightly worn cranks,
not undersize bushes.
Pleasse forgive any naivity I am an Electronic eng not a Mech. Eng.

[imack]

If you want a custom sized bush it may be worth contacting AC Dodd via Facebook. I think he offered to make a custom primary gear bush for someone on TMF who had a similar problem. I have a feeling he might have also had some original type deva material produced to make bushes from as well. No idea of cost though.

[Spider]

The original bushes as supplied as a spare part were about 20 thou undersize. After fitting, they need to be machined to size.

The original front bushes last time I look were still available.

I have the correct Deva material and make the Rear bushes.

[panda911]

Good evening.
After the failure through oil leak of my primary gear, Keith Calver volunteered to rebuild engine as it was
pot size on half shafts as well as floating front bush on primary gear, I may have to replace the top hat bush also.
But most importantly he objected the colour of the alloy rocker cover.
Seriously though I hoped that he might have the floating bush made.
Just as he had the second gear forks for 3 synchro and 4 synchro boxes. (marked with Calver ST)
In ten days time or so, will go to the dyno shop.
I will provide the dyno results.
BR
P

[panda911]

Keith did indeed have some in-spec floating bushes made, one of which he fitted to my primary gear.
Total float about 4.5 thou may be a lttle less. He has more left.
Engine was put on dyno and then delivered to have it put back in the car

[imack]

I'm interested to see how this goes.
Mine still seems to be holding back the oil and no clutch operation issues indicating binding bushes. Just had the starter out, and the flywheel is still dry.

[Rolandino]

I cannot see the benefits of running a primary gear with a floating bush. WHY?

[Spider]

I cannot see the benefits of running a primary gear with a floating bush. WHY?

Best I can see, it's intended to be a cheap repair, though, with those I've repaired, it's cheap and nasty. I have another coming in this week that ran one of these, it made a bit of a mess of the crank.

<Edit: one other thing to keep in mind too with floating bushes is that if the crankshaft is spinning, the bush will always spinning, albeit with foot off the clutch pedal, the bush will only spin slow, but it is spinning none the less. This only adds to heat where it's not wanted and while slow, the oil that's gong in there. >

[Exminiman]

I cannot see the benefits of running a primary gear with a floating bush. WHY?

I don’t think there are any benefits, it is a solution that is supposed to overcome the friction between the primary gear and the crank tail without using the old Deva material for the bush. While I have no desire to “Dis” the MS solution, at least they have tried to make a solution, it can just replace one issue with another. BMC obviously had lots of issues with PGs early on and took a while to resolve it, personally, I think they would of jumped at using a floating bush type solution if they thought it would work long term. The Deva bush solution gets rid of the oil issue , but does depend on the correct material for the bushes to replace the oil…….which is not always used.
Be interested to hear other opinions, as failure of PG is such a massive PITA.

[panda911]

Always keen to learn panda911.
Interestingly, last year I saw an FIA race mini with exactly the same leak with oil contaminated with clutch dust coming from between the starter motor and transfer case (and ultimately from the jiggle pin) that mine suffers.

Hi Imack.
Reporting a result on correctly specked?? front bush is taking longer than I thought as ADO are replacing door skins.