ausmini
https://www.ausmini.com/forums/

Changing idler gear
https://www.ausmini.com/forums/viewtopic.php?f=2&t=100092		 Page 1 of 1
Author:  Morbo28 [ Sun Jun 14, 2020 7:24 pm ]
Post subject:  Changing idler gear
Hi all,

I'm building up a spare 998 on a super-tight budget, 1967, remote change. I'm just looking at doing rebore, crank grind, bearings, pistons + rings, then get gearbox up to scratch.

During strip-down I identified the failure mode (interesting side-note, this engine was from a car last registered in 1980, meaning this engine was on the road for 13 years, then it has sat in its current state for 40 years. weird thinking this failure I'm looking at occurred when I was a 1 year old).

Idler gear is completely munted, flogged out the housing like so:

Image

I'm not worried about the housing, I have spares. What I need to figure out is how to salvage the gearbox casing, as I believe running it as-is isn't possible due to damage. Correct me if Im wrong - if you think I can just chuck a bearing in there and call it a day.

Image
.
Image

This is a low-cost build, so I'm after a cost-efficient solution. I am thinking I could either:
* Chuck a new bearing in it and get on with life
* Enlarge the hole to fit an a-plus idler gear (most likely this option)
* Enlarge the hole and press in a steel insert to run std idler gear
* Or even enlarge the hole to fit this as part of a straight cut conversion

Image

And how successful do you think I'd be using a drill press at home rather than machine shop...?
I would also need to know the exact ID for whatever solution I choose.

Thoughts?
Author:  Phil 850 [ Sun Jun 14, 2020 9:00 pm ]
Post subject:  Re: Changing idler gear
Looking at those photos, I suspect it might be the bearing only.
Pull the bearing out and see if the housing really is scored.
Author:  Morbo28 [ Sun Jun 14, 2020 9:45 pm ]
Post subject:  Re: Changing idler gear
Phil 850 wrote:
Looking at those photos, I suspect it might be the bearing only.
Pull the bearing out and see if the housing really is scored.


I'll be pulling it out during the week to confirm, but yeah good point. Maybe it isn't damaged enough to need enlarging. This close up does suggest to me the race has worn through to the housing, and it felt that way when I inspected it. But I guess it's not like the housing itself is a race for the needle rollers, the needle roller bearing does have its own outer race included.

Image
Author:  drmini in aust [ Sun Jun 14, 2020 10:19 pm ]
Post subject:  Re: Changing idler gear
The needle bearing case is thin, it will distort if the housing bore is worn oval.
Assuming it's not, the other problem will be the thrust face will now be worn more on one side. Can be fixed by milling it flat, face an equal amount from the housing flange also.
I've done a few due to wear, not had that trashed bearing problem though.

Be aware not all flywheel housings align properly on other cases. They are not identical relative to the dowel positions. No CNC machining back then.
Author:  IndigoBlueCooperS [ Mon Jun 15, 2020 8:21 pm ]
Post subject:  Re: Changing idler gear
Is this a three synchro box from a Deluxe? Should be able to find a second hand housing somewhere at a reasonable price.
Author:  Morbo28 [ Mon Jun 15, 2020 8:49 pm ]
Post subject:  Re: Changing idler gear
Thanks very much guys, info is appreciated.

Indigo, yes it is :) My philosophical approach for this build is to use whatever I already have wherever possible. So preferably I will find a way to make this current box work.

If it doesn't work out, I'll get another box.

The whole car is being built from left over parts :D

I was just given the lead for a shop nearby who has experience fixing this very problem, so I think I'll get him to do the machining.

I should be able to split engine and gearbox tomorrow to confirm what I'm dealing with.


Sent from my Pixel 3 XL using Tapatalk
Author:  Oscar [ Tue Jun 16, 2020 10:56 am ]
Post subject:  Re: Changing idler gear
We had the same issue in the same year believe-it-or-not!!

I had a spare clutch housing so that was good, but some of the gearbox casing bore had been carved out as well.

As the car was the wife's daily it had to be back on the road asap, so I filled the damaged area with Devcon Aluminium Putty, very carefully recut the bore with an adjustable hand reamer and put the car back in service.

Three years later I took the car off the road for a year and gave it a ground-up-bare-shell rebuild. During that process I checked the repaired bore in the gearbox and found that all was good, so I left it alone and just fitted some more new bearings and a new idler shimmed to minimum spec.

36 years on we still have the car and there's never been an issue with my "temporary quickfix" to the gearbox.
Author:  Morbo28 [ Fri Jun 19, 2020 7:14 am ]
Post subject:  Re: Changing idler gear
Only just saw this reply, wow that's great that it stood up so long!

I'll contact a local guy to machine it if needed. Life got in the way this week, so I'll be splitting the box and block in the next few days so I can have a better look with the remains of the bearing out.

Sent from my Pixel 3 XL using Tapatalk
Page 1 of 1 All times are UTC + 10 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/