4 replies to this topic

[Gilles1000]

Hello all

 

I bought a 1275 engine for very few quids, my plan is mostly to learn how the Mini engines are built (and maybe repair it).

The previous owner explained that the engine had metal chips in the oil and had in the end only oil pressure from 1500rpm.

 

Now I disassembled the engine completely to see where the issue comes from. It seems it had an idler bearing failure, which resulted in blocking the oil filter, damaging the oil pump and preventing oil to go to the main journals on the crank and camshaft.

The crank is damaged but I think it can be reground, the cam bearings are gone.

 

Now to the gearbox: I plan to use it for my project as I plan to build an A+ engine for it. I could rebuild the box now and save later time when I will start the engine rebuild.

My main question is on the housing for the idler bearing: do you think I can still use it? I cannot see a problem as there is minor wear, I could barely see the wear with a ruler to compare the flatness with the ribs close to it.

 

 

And the 1st/2nd selector fork (on the left on the picture), does it have a normal shape? To me it seems to be missing some material, although on pictures form new it looks somehow similar.

 

 

 

To the rest:

 

The flywheel case looks worse, but again, does something prevent for reusing it? the wear is not deeper than the needle bushes.

 

 

The idler is ready for the bin. one teeth is broken and the shaft is 1mm thinner than it should be...

 

 

The primary gear. This has a chip gone on one teeth, and the oil shield is worn. I saw that Minispares does not build this shield anymore, so I could remove it and live without it? What about the chip, I know one should be very critical about pinions. Anyway, I do not need it as I have another primary gear on the other engine.

 

 

Would you consider a complete rebuild kit or would you reuse the gearbox bearings if OK?

 

Thank you for your help,

Gilles

 

[coopertaz]

idler and primary bin, if you remove shield (oil flinger) from primary seal will leak and do clutch. Flywheel housing scrap, you can also buy these secondhand in good condition. Gearbox case if only minor wear, then an enineering shop shouild be able to machine it flat, you may get away with it as it is but remember it's a thrust face so if it throws idler bearing out of true then you will repeat failure. With selector fork if thrust faces are ok then will be useable and if rebuilding a box always use bearing set especially if bits of metal flying around in oil, you say it's goosed mains so bearings have had same oil in.

[Spider]

I've repaired loads of gearbox cases and flywheel housings like those. Sometimes just a lick in the mill on the thrust faces is all that's needed, then going to thicker thrusts. Some I have also taken a lick off the gasket face of the flywheel housing to keep the thrusts needed in a standard size, others I have made thicker thrusts for.

I'd strongly suggest though, having the housing properly aligned to the the gearbox case, many times, from those failures here I've seen, have been caused from poor alignment here from manufacture.

The Idler Gear is karput (had it). The Primary Gear I wouldn't be too quick to through out. I see the slinger is fairly minced up, but that can be changed from just about any other primary gear. I know new Primary Gears are available, but, those I've seen,,,,, suffice to say, recondition the old one ! The slingers are important to stopping oil leakage through the seal. You could go to an MPI Seal and it shouldn't leak here, but these wear a groove in the seal face on the gear.

The wear limit on the selector forks is 0.015". Without measuring, I can see yours there for 1st / 2nd is well over that ! When these are work, they won't allow the synchro hub to fully engage on the dogs, which will result in it jumping out of gear. After it does this a few times, the dogs round off and it won't hold gear.

[Gilles1000]

Thank you both for your input!

 

That sounds interesting if I can reuse most of the parts, I'm not keen on scrapping stuff...

 

That's strange what you are saying about the oil slinger, I just looked again on Minispares for the A+ 1275cc primary gear they say:

 

"Genuine Mini Spares primary gear for A plus 1275 engines with 29 teeth-

Now with Mini Spares easy change front floating bush held in by circlip from March 2016 to save any future costs. No longer fitted with oil slinger.

A+ 29 tooth Primary Gear"

 

Spider, how do you see the wear on the fork, is it the axial gap between fork and synchro?

And for the alignnment you are talking about, I do understand it's the one between the gearbox housing and the cluth housing where the idler sits at both sides?

 

Cheers,

Gilles

[Spider]

Hey Gilles,

I didn't see the chipped tooth in the Primary Gear you have, all the same, unless you are building some high output road burner, polishing that chip so there's no stress risers that it can crack from will be fine. If you are not crazy about that, finding a used gear shouldn't be too much of a mission.

I can see the wear in your fork here (red arrows)

 

 

The blue arrows too I can see the thrust faces are not parallel.

This type of wear is fairly typical for the 1st / 2nd fork. The 3rd / 4th fork has much long and continuous thrust faces and while it should be checked for sure, they are usually in servicable order. You can check the clearance using a feeler gauge. I have a set of narrow (tapered ?) nose feeler gauges that I find make this a little easier to do.

There was a thread a little while back where we discussed the misalignment issues of the flywheel (transfer) housing, the issues that it causes and how some have gone about resolving it;-

https://www.theminif...roller-bearing/

 

While I made dummy shafts, a machine shop (general jobbing type), would likely be able to clock everything up without making dummies (Vizard describes a technique for doing this) and I would imagine it would only be an hour or maybe two's work for them. Well worth doing and regardless of what casings you want to run with, they'll all have similar issues to more or lesser a degree.