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Front Primary Gear Bush Failure


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#1 morley

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Posted 11 March 2010 - 12:27 AM

Bit of background info:

had a new engine fitted; a 1293 with everything new, new pistons, bearings, primary gear bushes, clutch, cam.. the lot
The gearbox was built buy a member on TMF it's a minispares's A+ GT ratio with xpin diff and only done 500 miles when bought.

all was fine and dandy until a week of use when it all started off when i couldnt put it into 1st gear after i went to pull away after stopping.. so i ended up just turning the engine off and selecting first and starting it up and doing it that way.

then after that sometimes when i put my foot on the clutch it would lock down, and would take some real force to get it back up. and now recently which has made it undriveable.. and i had trouble selecting gears when the engine is switched off with either my foot on the clutch or not, and once or twice it has got stuck in reverse and i literally have to kick the gearstick to get it out of gear. It would not into gear when the clutch was down.

I took off the 'wok' to check if their was anything noticeably wrong but all looked good apart from the release bearing was slightly 'blued' in one place but still moved freely, so i thought this was just the slave cylidner. replaced it and...

bled the clutch, had a leak at the slave cylinder end on the banjo so that was sorted with a new copper washer. bled again. And still the problem remains :S just wont go into gear with the clutch depressed [engine on]just grinding noise. I tried adjusting the throwout, followed the haynes [push clutch in and out, then hold down, tighten the throwout nut until it hits the wok, release clutch, turn in one flat and tighten them together] and the arm just didn't seem to move enough for the clutch to engage.

so i investigated some more and found that the primary gear was really tight and took a while to get it off.

Posted Image]

Posted Image

the bush is just really loose in the gear and comes out easily!



where the crank is shiney, it isn't deep at all, can't even feel a ridge with my fingernail so nothing to worry about there thankgod!

just been on the minispares website and basically is says that the front bushes are common to fail after fitting new ones :? so don't know how to fix it really.. i have a few options:

1.cheapest is to get a new bush fitted, but have the risk of it happening again.

2.or i could get a second hand primary gear and fix clearances with thrust washers but its slightly more expensive .

3.or straight cut drop gears, a good idea seeing as the engine is apart but very expensive unless i find some second hand ones which is a pretty rare occurance!

The two biggest outstanding symptoms were severe oil leaks onto the flywheel/clutch assembly, and difficulty/impossibility in selecting gears. Strangely, these problems were still suffered immediately after refurbing the offending article, using ‘modifications’ suggested by some of the many Mini ‘specialists’ out there who all but guaranteed it’d cure the problems! And that’s a right dis-chuffer! Some bought new gears from other ‘specialists’ who make their product ‘special’ by using ‘specific machining detailing’ to ‘cure the problem’. Unsurprisingly these didn’t work either.

Front bush damage is caused by it becoming loose, spinning between the gear and crank, and generating an enormous amount of heat. This ruins the bush, destroying all clearances, and allows excessive amounts of oil to pass – both through the now much larger clearance between crank, bush and gear, and past the primary gear seal. The latter happens because the primary gear wobbles about excessively so the sealing lip on the seal can’t do its job. Slightly less severely super-heated bushes causes them to move outwards, jamming the primary gear between the retaining clips and the thrust washer and crank shoulder. This is why gear selection becomes difficult/impossible. The primary gear won’t disengage drive from the engine, and is the main reason why the rear bush gets it’s thrust lip broken off. Even if the loose front bush isn’t immediately apparent. This lip does break off on it’s own though, but for the same reason all the other problems occur.



The ‘miracle cures’ to this have been legion over the years. Despite much nose-tapping and eye-winking, almost all solutions revolve around two themes - running a much bigger front bush to crank clearance and/or welding it to the primary gear. As many can attest to, even this doesn’t work. That’s because the cause isn’t being addressed. And that’s EXCESSIVE HEAT.



It’s generated by the slipping clutch – be that when gear changes are made, getting off the line, or badly set-up clutch. Magnified by the use of cerametalic plates. The slipping causes friction, generating a huge amount of heat. This spreads through the plate and into the primary gear. When the heat level becomes excessive, the bushes pinch on the crank, grabbed, and spun. Disaster. Results as above. The cure? Initially and mainly -reduce the heat level. Simply achieved by either boring holes in the clutch cover (‘wok’), or by welding on a suitably sized and positioned duct. Whichever, always cover with meshing to deter foreign objects from joining the fray! Secondly – further proper development. And that’s just what I’m doing – so keep your eyes open for the results!


So not really sure which one to go for and how to fix it? does anyone have any suggestions??

thanks.

#2 jonny d

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Posted 11 March 2010 - 10:04 PM

I seem to have read somewhere that minispares have solved this one with a special slipping bush, that dosnt need reaming after fitting and is almost guaranteed not to bind up get on there website and have a look. (hope i havnt dreamt it lol)

#3 m1n1

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Posted 11 March 2010 - 10:51 PM

I had the same problem as you a few years ago; i was rebuilding my engine and whilst at it i bought new bushes, took them and the crank to the machine shop and had them reamed to size to suit the crank.

When it seized on i was somewhat angry; but went down the route of the floating bush and.. i it did the trick!

#4 dklawson

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Posted 12 March 2010 - 02:28 AM

The floating bush is a good idea but it appears Morley already has the floating bush. It's the part that's "out" of the gear resting on the table.

I had not heard of this problem with the primary gear bushes. When it was time to repair mine I bought the bushing from Mini Spares and bored it to size at work. Since there is no lube reaching the system while running I put moly lubricant on the crank tail before assembly. I don't see how else you could provide lubricant to prevent the failure apart from using a bushing made from sintered bronze filled with oil.

#5 MRA

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Posted 12 March 2010 - 11:11 AM

using silicon bronze bush will help. but the best option is a floating bush....... just not brass >_< brasss holds little in the way of lubrication unless as Doug says it is a sintered brass which would need specialist sintering mould tools and machinery........ in other words ££££££££ :)

#6 morley

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Posted 12 March 2010 - 06:21 PM

yeah the bush already fitted is the floating bush http://minispares.co...mp;tc=1#submenu

so i am not really sure how to fix it ;) could i perhaps get another bush the same and have the risk of it happening again!?!?

#7 Sprocket

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Posted 12 March 2010 - 07:13 PM

What is the real problem?

Looking at the primary gear thrust bearing, the chamfer might be on the wrong side, cant see for sure, but that in itself would cause the primary gear to lock when the 'C' lock washer is fitted.

Edited by Sprocket, 12 March 2010 - 07:17 PM.


#8 morley

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Posted 12 March 2010 - 09:44 PM

the problem is that i can't select gears whilst the engine is running, i thought it was the slave sylinder at first and on further investigation i found that the primary gear was really tight on the crank and the front bush really loose.. all the sypmtoms/problems are in my first post ;)

#9 Sprocket

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Posted 12 March 2010 - 10:03 PM

please explain 'tight'

is the primary gear tight with the 'C' washer and the backing washer fitted? or is the primarly gear tight without those?

The latter would mean the rear bush is tight when the front bush is a floating 'loose fit' bush

The primary gear gan be difficult to remove if there is a slight burr on the groove for the 'C' washer.

I am just not sure which bit is 'tight'

#10 morley

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Posted 15 March 2010 - 07:31 PM

the primary gear itself is very tight on the crank, this is due to the top hat bush being really really tight on the crank :P




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