7 replies to this topic

[Itsjustanestate]

I am currently rebuilding a SCCR gearbox having destroyed the layshaft and its needle roller bearing. I am just wondering if there has been any experience with replacing the small needle roller bearing with a phosphor bronze solid bush. I know in some modern competition boxes this is often a modification used as it is stronger than a needle roller due to greater bearing contact area and thickness of the bush, but I have not come across this in for the mini. One would think it could also be done for the drop gears.

 

Anyone able to share any knowledge on this as I am tempted to knock one up and give it a go.

[Cooperman]

I have a vague memory of some early gearboxes which had a phos-bronze bush(es) in the gearbox which were re-designed to take a needle roller bearing(s) for better reliability.

John (GuessWorks) would know.

[Spider]

The early 850 'A' type gearboxes did indeed have bronze bushes on the 2nd and 3rd gears, however they burnt out pretty quick (even though when moving on the bush, they were fairly unloaded) and then they went to needle rollers. This was listed by BMC as the Third Major Design Change to the Mini's Gearbox.

 

Bushes are great for low speed high load applications like suspension parts but not too good at all at high speed applications.

 

I've found 99% of replacement Layshafts out there these days are utter rubbish. If they have any hardening on them, it's only wafer thin. For this application, it has to be a minimum 0.030" deep. otherwise as the rollers run over it the hardened layer flakes off like an egg shell. Once the hardening on the Layshaft goes, the needle rollers pack it in very soon after.

 

If it's for the A+ style Gearbox, try Swiftune.  Dare I say it, but if it's pre-A+ type try Minispeed's Competition Layshafts, but don't buy over the net or on a phone call, go to the counter. Sadly, Swifty doesn't do these.  If you're really stuck, drop me a PM, I have them made to my own design, while they are not cheap they will not ever wear out as long as there is some Oil in the Gearbox.

Edited by Moke Spider, 18 December 2015 - 06:50 AM.

[carbon]

Also when you do get a replacement layshaft do check it is straight. The last one I got from reputable supplier was about 20 thou off-centre, not a lot but enough to cause the laygear to bind and not rotate smoothly.

 

This was a competition layshaft for a pre-A+ 4-syncro gearbox.

[Itsjustanestate]

Thanks for the replies so far.

 

I ask the question as I am running A+ and have assembled the laygear with new performance layshaft and new roller bearings and I am not happy with the play in the small roller. The lay gear is unmarked and shows no sign of wear so not sure what is going on unless the new layshaft is under size.

 

I guess phosphor bronze would need more oil and being reliant on spray always has a risk. One though was to put an oil feed into the layshaft and make oil swirls in the bushes.

 

The good thing about phosphor bronze is if it does fail it will cause very little collateral damage.

[Spider]

Regarding the play you are seeing, I did actually forget to include a small bit on bearings (that are sometimes supplied these days).

 

Some that I have been supplied, sometimes in boxes that don't look familiar, I've noticed that the needles are a tad shorter than the originals and some are even spaced out such that there is one less needle!

 

These days, I insist on genuine IRH ones (which is now owned by Timken).

 

Another few other aspects of this is how well the Laygear was made as I doubt it would be a genuine one, also, it's not uncommon for the bore in the gearbox casing (particularly on the small end) to wear giving the feeling that the layshaft is worn.

 

The bronze bushes that were fitted in to the early mini gearboxes were manufactured in a way that had 'force fed lubrication' and then for a short while modified such that they did include 'positive lubrication', before going back to 'force fed'. The 'problems' with bushes can be cured by lubrication methods to a point (pressure fed via a pump), but IMO, when everything is done right, bearings run rings around bushes for this application.  Sorry, but if I can suggest, I think you are getting caught up in thinking that this is a design issue when in fact it's faulty parts. The only time I've even seen the A+ type layshaft wear at all is when the gearbox is run very low in oil for extended periods and / or, goes without regular Oil Changes. Blown head gaskets if left will also ruin layshafts (and gearboxes in general).

 

Bronze can work harden and when that happens, it will wear any steel shaft in no time.

Edited by Moke Spider, 18 December 2015 - 08:10 PM.

[Itsjustanestate]

Great advise. I was just exploring stronger options and I know in a lot of applications including some competition boxes people are going back to bronze bushes for strength.

The reason the bearing went was because the lay gear is a JK SCCR Metro challenge item that had been sleeved to go into a pre A+ box and layshaft arrangement. God only knows why. I bought the box from a company who reconditions mini boxes and they put it in an A+ casing for me but unknown to me used all the old layshaft presumably because they couldn't get the bush out easily. It did a full season of rallies before letting go so no real comeback and a lot of time has now passed.  It looked like the hardening on the bush gave up. I machined and pressed the bush out without damaging the laygear. 

 

Looking at the new needle roller bearing I have purchased it is 11 roller unit not 14 roller but to be fair this was stated by the supplier so that explains the play. I am on the hunt now for a 14 roller timken bearing. 

 

Interestingly, the lay gear looks like it is machined deep enough so that it will take 2 of the small roller bearings. Was this intended by JK?

[carbon]

Could be worth taking advice from John at Guessworks on what combination of layshaft and bearings would work best.