Idler gear issue - 3 vs 4 synchro

[ricardo]

A friend of mine showed me today a few pictures of his recent restoration process.

This included an engine rebuild - MK1 Cooper 998 - in which he decided to fit a fully synchronized box, rebuilt by known expert.

1)
Seeing the pictures, I realized that the idler bearing (box side) doesn't have (or looks like it doesn't) the clutch side circlip.
This is a 4 synchro box, so should have 2 circlips, one each side of the bearing. The box side circlip seems to be there.

Here is a picture of it. I can't see the groove for the circlip, so the bearing may be out of position too.



I don't know how tight the bearing is in the case, but I'm wondering why the person who built the box didn't fit it.
Do you think he should have any problems? Is this a common practice?

2)
He used the original idler gear, which is shorter (box side) than a 4 synchro gear. This means that the shaft may be running only on half of the bearing as the bearing does not sit flush with the box like they on do on 3 synchro boxes.

I can't make any trial fit at the moment, but visualizing it, I'm seeing a problem.

The engine is running fine and the car is on the road. Do you think he should strip it and replace the idler gear and fit the circlip or this shouldn't give any problem? I'm not liking the idea of a 3 synchro idler on a 4 synchro box.

[ricardo]

This is an early 4 synchro box, 22G1128 case.

[Vegard]

Why would you really need the circlip? If the bearing gets loose, the circlip won't help one blind bit.
Forget the circlip!!

[ricardo]

Ok. What about the idler gear being the 3 synchro type? Isn't this asking for trouble?

[Vegard]

Ok. What about the idler gear being the 3 synchro type? Isn't this asking for trouble?

You have to use the bearing that fits the casing. As easy as that. I've seen lots of 3 syncro bearings wihich have survived a good deal of power.
What are you putting on top of the box?

[Michael7]

I would be worried only if there is no circlip on the gearbox side of the case. If it was missing, the bearing could possibly "walk" inward and then there is a major problem. This would happen sooner with the short pin of the 3 synchro idler gear.

In fact, I don't recall a circlip groove outside of the bearing in the 4 synchro, since the thrust washer would prevent it from going anywhere. I don't have a gear case here to look at, but I doubt there is one, although some cases could be different.

Note the 3 synchro idler bearing 88G302 (same as the front suspension upper a-arm, by the way) is 1.004" in diameter. It would have a very obvious loose fit in the 4 synchro case, which is the point that Vegard makes. The proper 4 synchro bearing 13H7848 is 1.065" diameter. The 2 bearings are slightly different in design and it appears the correct bearing has been used from the photo. The 88G302 has tiny rollers that sit against one another and the 13H7848 is like the one in the photo.

[ricardo]

@Vegard,

The issue is not the bearing. The bearing fitted is the correct 4 synchro bearing (1 1/16'' ext and 3/4'' internal diameter).
The 3 synchro bearing has different outside diameter, but inside it's the same as both 4 and 3 synchro idlers have 3/4 shafts.
But again, the problem is not the bearing.

The issue is the idler gear.
It got me worried knowing that they fit a 3 synchro idler which has a shorter shaft/pin than the 4 synchro on the box side.
If I'm not mistaken, the idler shaft will only run on half of the bearing.
In a bad case scenario, this can cause wearing/fatigue on the bearing and gear, thrusts and in ultimate case, the box case, etc.

At the moment, the engine is finished and running well.
This is a friends engine that was recently rebuilt and I was shown the rebuild pictures today.
So, it's not a matter of deciding what to fit or even check to see if it fits well or not. The engine is running.



@Michael7

The box has a circlip on the laygear side.

Here's a picture of other 22G1128 with a circlip on the clutch side. The picture is cut, but still noticeable:



But my concerns now are only regarding the idler gear fitted. Thanks for your reply.

[LMM76C]

I'm confused by references to the 3 synchro idler gear being short pin and the 4 synchro being long pin. Surely the short pin gear was replaced in production by a longer pin gear (still in the 3 synchro production time frame) as a direct result of Timo Makinen's retirement on the RAC Rally from bearing failure with a short pin gear?
I recall fitting the long (inner) pin gear to a standard 3 synchro box that previously had a short pin gear and using a new but original type bearing. The short pin gear was clearly a weak point. IIRC a different type of inner circlip had to be used to fit the longer pin gear to the earlier box, to allow the pin to pass through the circlip.

[Mini4Ever]

3-synchro and 4-synchro idler gears are interchangable with use of originally sized idler bearings.

I tend to put 4-synchro idlers in 3-synchro boxes with the idler bearing in the gearbox casing fitted as far as possible to the gearbox side. The bearing sits quite firm in its slot and would not come loose under normal use. It is better to fit the circlip, but you may need a different one when using a 4-synchro idler in a 3-synchro casing.

4-synchro idlers have one shaft end (the gearbox side) longer than 3-synchro idlers. 3-synchro idles have both shafts of equal length. To my knowledge, 4-synchro idlers where not fitted in 3-synchro boxes by the factory.

[Vegard]

Why fit circlips at all? It's 2011! If you guys don't trust (no pun intended ) the idler bearings to stay put, apply some Loc Tite products.

[LMM76C]

To my knowledge, 4-synchro idlers where not fitted in 3-synchro boxes by the factory.

When did the 4 synchro box first get fitted to the 1275 S in production?
The new long pin gear was produced very quickly in 1967 following Makinen's retirement from the lead on the 66 RAC in Kielder. At the time it was always referred to as the long peg idler gear, rather than the 4 synchro idler gear, and was understood to be a 3 synchro production item.
As I posted before, the long peg gear required a different inner circlip with the existing bearing to allow the gear peg to pass through the circlip where the short peg gear did not extend beyond the inner end of the bearing.
I wouldn't fancy using no circlip, as suggested above. "Good engineering solutions" are usually safer than copious loctite. Having said that, I knew someone back in the day who fitted a SC/CR gear kit to a 4 synchro box without the layshaft circlips and had no immedite problems, despite asking me what the 2 spare circlips were for....

[ricardo]

A picture paints a thousand words, so here they are:


3 synchro on the left. 4 synchro on the right.




This is more or less how a 4 synchro idler fits in a 4 synchro box (22G1128)




And this is how my friends engine should be right now. 3 synchro idler in a 4 synchro box. If it was mine, I would strip it and replace the gear.




Just for curiosity, this is the referred problem with the 4 synchro idler in a 3 synchro box (22G333). It is hitting the circlip, so you need to use a different one.




Still regarding circlips, if I have them, I will use them. At least on the laygear side, I think it should always be fitted.

[Vegard]

Still regarding circlips, if I have them, I will use them. At least on the laygear side, I think it should always be fitted.

I don't understand why, but I guess it's horses for courses. If you remove the cicrlip you can easily fit the 4sync idler.
Job done.
As mentioned previously, if the bearings starts wandering, then the lack of circlip is the least of your problems.
Has anyone ever had a idler bearing move?