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Hello Guys

After some troubles with my MED primary gear

we made a modification on the floating bush

Does anyone ever experienced it?

What troubles were you experiencing?

I had some troubles, the primary gear was stuck on the crankshaft

Engine builder modified a new bush to avoid the problem and to have a little bit more oil on the bush

is it a good or a bad idea?

In my experience ‘they all do that sir’.
Your fix may work, but I’ll be surprised. The answer is really to get a fixed bush kit in and taken out to size.

Its a brand new bush, but the engine builder decided to modify this way

Just want to be sure it's a good idea, but of course it will be bored to exact size

Any thought?

I Agree with GraemeC. I would fit a fix bush

You can't, you have to put a floating bush..

Seems to be a bit of misunderstading here...
You fit a new bushing to the gear and 'ream' it to the size the workshop manual says it should have.
Meaning there will be the clearance between the gear (bush!) and crankshaft there should be!
Its a matter of few hundreds of a millimeter clearance.
When building an engine one has to check every measurement so there is the right clearance.
Even if every part is new and should be belived to be right! Unfortunately that to often isnt so!

Personally would not trust this modification that has been done now, rather have polished the inside of the bush that was there first with a wet 5000 grit 'sanding paper' until it mowed freely. But thats just me!

Only time, and oilpressure will tell what works best.

As post above , I think you should check size of new gear or bush and ream to size if required.

This video from AC Dodd is in two parts (this is part one) it runs through the whole process of re-bushing a primary gear.

Which may be more than you need, but vids will give you an overall view.

Looks like your engine builder is trying to mod this bush to work a bit like a main or big end bearing shell….i am not sure this will work, might also weaken the bush and might cause a stress crack to start?

It may be that you engine builder does not have the ability to ream the bush's to size ?
,
https://youtu.be/wYo4brhdfss

Yes, some misunderstanding but mainly in those last two posts.

It is a floating bush - it shouldn't need any reaming. They are designed to allow them to spin on the crank and in the gear, however they generally nip onto the crank and the gear spins round them.
http://www.minispares.com/product/Class ... |Back%20to

You can replace a floating bush with a standard type bush, although depending on the gear you may need a custom one to be made.

I don't think the mod will work - I presume it is an attempt to get more lubrication between the bush and the crank, however it will do the opposite and let oil get behind the bush easier, promoting it to spin. The groove on its own may help, although will introduce a weak point as mention, and may cause the bush to fail completely.

I certainly wouldn't make that mod.

Hello everyone.
I see that a lot of people are wrong about several things. the primary gear in question is a model with a floating bush. it is not a matter of machining a fixed bush like a standard primary gear. then someone also talks about a floating bush but it is not the right one because the one in question is narrower. it is held by a clip. the problem with charles is that this so-called competition part seized twice on the crankshaft. the first time it is the floating bush and the second time the front bush. I add that the tolerances were correct in every way. given the design of this assembly I do not see how the oil can lubricate between the bush and the primary gear because the bush is well trapped between the step and the clip. so when it no longer turns it is the part between the crankshaft and the bush that turns, but the tolerance becomes insufficient so that it does not also seize. therefore the modification serves to distribute the oil on both sides of the bush and thus always keep it wet ?

alexis1300s wrote: ↑Tue Nov 16, 2021 11:33 am the primary gear in question is a model with a floating bush. it is not a matter of machining a fixed bush like a standard primary gear.

You can and I have, but it may need to be a custom made bush, not the off the shelf one

For me, the floating bushes are not a good solution. I have had problems with them on many occasions - usually they seize to the crank and although they continue to work OK, the problem becomes apparent on strip down. This is fine with the ones without a clip as the primary can still be taken off, the ones with the clip means the primary gear becomes stuck.

Is the build for competition use?

Hello Graeme

Only road use, fast road engine that might be used for trackway but will spend 90% of its life on road

the old primary gears had to be improved by something that is less reliable!
The failure of the bush is due to heating and seizing! the lack of play and lubricant on the 2 sides of this floating ring seems to be the cause.
I don't think increasing the game a bit and creating this oil path will fail! in any case, reassembling the new floating bush without doing anything will only lead to a further failure.
Some runners seem to have even tried to change the type of bronze for this bush without more success ... if my method works I would have to file a patent so that you give me money to do the same thing