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Some of you may recall I had an issue with a Jack knight straight cut box a few years ago.
As an update the car is now on the road and I'm currently about 260 miles into my running in.
Everything was going well until the last 20 odd miles when I got a gradually worsening issue with 3rd gear crunching changing down from 4th.
The gearbox had been stripped and rebuilt before installation and bearings ect replaced that showed any wear.
I cannot recall if the baulk rings, springs and ball bearings had been replaced or not ( the box was supposedly unused but an issue was found with a gear tooth so was stripped for inspection).
So the question is, what do you guys think the problem is AND if I dont downshift to 3rd will I be safe for another 200 miles as I plan to remove engine and box for inspection once I get to 500 miles.
For reference the car never exceeded 3000 revs in the first 200 miles and has only been raised to an occasional 3500 revs in 4th only.

If you double clutch on the downshifts it won't grind.

Thanks Larry but on a very short drive I did try this and it was still crunching.

Double clutching on downshifts does nothing, unless you blip the throttle to bring the revs up to match the third gear speed.......

If the only issue is one of Synchronisation of 3rd Gear and it's not making any noises, then yes, it will be fine to continue driving with, but I would suggest avoiding any further grinding of 3rd gear.

Because the cause is unknown at this point, you risk the probability of it getting worse and potentially causing metal filings going through the fresh engine. I wouldn't gamble.
Paul

At the very least, I would drop the oil right now, and, see if there are any crunchy bits in there.......

Sounds to me like it’s either a worn baulk ring and/or the gear itself.

If its a JK gear kit, then it's probably the sychro face of the gear at fault, JK were legendary for poor quality & minimal QC for the last few years of their production.

Any crunched bits of metal "may" find their way through the oil pump, but won't get round the bearings as there is an oil filter between the two.

Thank you all.
I currently have the oil draining and will leave all day before i refill.
The oil certainly had no "large" chunks in it as used a sieve just to check.
There was a few filings on the sump plug magnet but I certainly have seen worse.
The gear box seems to be a metro challenge box so I dont know if that falls into the area of timescales of poor quality control?

The gear box seems to be a metro challenge box so I dont know if that falls into the area of timescales of poor quality control?

Probably NOT

Well after leaving it to drain the oil over night, this morning I filled up with Halfords 20/50 classic oil and took for a drive.
It now wants to crunch going from 2nd to 3rd assell as the 4th to 3rd so I am now forgetting about 3rd gear completely and have decided that I will remove the engine and split the box next weekend.
I am now on 280 miles and should get a few more on it over the next week and then just be a little gentle once its sorted and back in.
I fear Mark is correct about an iffy 3rd gear.

As a further update, I discovered that this morning after a 10 mile drive that I could go from 2nd to 3rd ok so not sure if it's an oil tempreture or a gear /metal heat expansion that is making the difference.
Has anyone else experienced this before?

underkut wrote: ↑Sun Aug 30, 2020 9:29 am As a further update, I discovered that this morning after a 10 mile drive that I could go from 2nd to 3rd ok so not sure if it's an oil tempreture or a gear /metal heat expansion that is making the difference.
Has anyone else experienced this before?

The Baulk Rings don't cope too well with cold Oil, especially when it's fresh.

Maybe a silly question, but is the clutch disengaging correctly? Seems a bit odd to have spread to other gears...