Gearbox bushes

SteveBorland · Feb 18, 2023

In Mick Hemmings exellent gearbox rebuild video, he mentions that the bushes in the 2nd & 3rd gears which spin on the shafts should be free floating.
I replaced the gears in my MKII with an almost new set from a MKIII from Fleabay. As fares I can see, these are 100% original, but one of the bushes is definitely not free floating, while the other is a lovely sliding fit.
How critical is this? I could make it a floating bush with a bit of wet&dry and some time.

marshg246 · Feb 18, 2023

A little more study first. Is it the bushing, gear, or shaft. In other words, if it's not free floating in the gear and on the shaft the bushing as probably taken a hit and is out of round. If only one, then its probably not the bushing - look for burrs in the gear or on the shaft. Try your old bushing. They usually last a long time if the gear oil is maintained.

RoadScholar · Feb 18, 2023

Measure ID and OD of the bushes, measure OD of shaft and the ID of the gears. I don't have the part(s) numbers for the bushes, but, on a bench, you can swap them. These steps will tell you what is responsible for the tightness. Purchasing a new bush may just solve the issue.

However, if you are committed to making this happen...

Always a good idea to check the shafts for true if you haven't already done so, new or not. Polishing the non-toothed sections of the shaft with a 1500 to 2000 grit wet/dry, then a final with crocus cloth.

If you need to alter the ID or OD do not use any type of abrasive; doing so will embed the abrasive in the bush. If the tight fit is is with the gear you can use an abrasive on the gear bore, but do wash the gear before test fitting the bush. If the tightness is with the ID of the bush a reamer, used very gently will open it.

I applaud your attention to detail!

Best

YING · Feb 19, 2023

RoadScholar said:
Measure ID and OD of the bushes, measure OD of shaft and the ID of the gears. I don't have the part(s) numbers for the bushes, but, on a bench, you can swap them. These steps will tell you what is responsible for the tightness. Purchasing a new bush may just solve the issue.

However, if you are committed to making this happen...

Always a good idea to check the shafts for true if you haven't already done so, new or not. Polishing the non-toothed sections of the shaft with a 1500 to 2000 grit wet/dry, then a final with crocus cloth.

If you need to alter the ID or OD do not use any type of abrasive; doing so will embed the abrasive in the bush. If the tight fit is is with the gear you can use an abrasive on the gear bore, but do wash the gear before test fitting the bush. If the tightness is with the ID of the bush a reamer, used very gently will open it.

I applaud your attention to detail!

Best

Bill,
Where do you find a reamer like you talked about.Are they adjustable or are they fixed for a certain size.Excuse the ignorance.
Thanks,Mike

Grandad · Feb 19, 2023

^^^ Reamers can be both ....

A UK seller ......... https://www.tracytools.com/ The US will have similar sellers

kommando · Feb 19, 2023

Adjustable reamers can be problematical in use, the depth of cut it will take is difficult to know in advance, too little depth and it rubs instead of cutting, too much depth and it digs in and overcuts or just stops dead. Had mine for 40 years and use is very limited, just too Goldilocks in nature for me.

marshg246 · Feb 19, 2023

kommando said:
Adjustable reamers can be problematical in use, the depth of cut it will take is difficult to know in advance, too little depth and it rubs instead of cutting, too much depth and it digs in and overcuts or just stops dead. Had mine for 40 years and use is very limited, just too Goldilocks in nature for me.

Agreed, and I bought two sets. Cheap and expensive. The cheap set does not work at all. The expensive set works but is nowhere near as precise as a correct-size non-adjustable reamer.

RoadScholar · Feb 19, 2023

YING said:
Bill,
Where do you find a reamer like you talked about.Are they adjustable or are they fixed for a certain size.Excuse the ignorance.
Thanks,Mike

Reamers are all over the place, but as mentioned below the fixed is better than the adjustable. Purchasing a new bushing (or 2) would be less expensive, time consuming and judgmental. For my part I realize that I haven't made all the mistakes that spring from poor judgement. "good judgement comes from bad judgement" and accompanied with a tuition invoice...

Best.

Devondan · Feb 19, 2023

As I recall my bushes were tight, I removed them and put the new ones on from an RGM kit and they floated perfectly, I guess the bushes can tighten up in use.

Gearbox bushes

SteveBorland

marshg246

RoadScholar

YING

Pittsboro,NC

Grandad

kommando

marshg246

RoadScholar

Devondan

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