4 synchro remote change g/box with new Rover baulk rings - using Penrite 20w60 HPR30 Mineral oil


I have noticed recently that after driving for 20mins+ that i have trouble selecting gears. When the engine is cold or first driven there is zero issue, it selects gears nicely but once hot I struggle to select gears (mostly 2nd & 4th)

I have recently flushed/changed the clutch fluid as i thought it may have had moisture in it. - issue is still there.

It is most noticeable when attempting to change gear while the engine is under load, but if I am paying more attn to the RPM and when i select gears, it is somewhat better..

I'm really hoping not to have to pull the engine again as the engine is only 12months old, the gearbox was pulled apart, cleaned, baulk rings replaced and reassembled by my step father (retired mechanic) but this is starting to make long trips unbearable and extremely frustrating.

Any thoughts or suggestions on what the issue is?

Thanks in advance.

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1964 MORRIS 850 - POST ZOMBIE APOCALYPSE CAFE RACER INSPIRED.

https://spotify.link/D0P4KtIP2yb

1098 +0.40
266 Kent Cam
GR Flat top pistons
HS6
1.3:1 Roller tip rockers
Stupid high CR

Oil might be too thick for a tight box. As it heats up the tolerances get tighter. Thinner oil is best for a new box and thick oil for a worn box

Have you tried adjusting the clutch up to rule that out as a potential cause?

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-----Better is the enemy of good-----
-1976 Yellow Devil Leyland Clubman-
-1970 Morris Mini Van - Work in progress-

its very odd only thing i could think of is possible crank end float set incorrectly when clutch is pressed when hot does engine die down/stall as the end float is listen wrong in the book

Make sure the clutch lever components are in good condition. Had similar problem and found clutch lever had a crack in the ball head so as the motor got warm, the crack widened and the geometry of the level changed and thus made gear change clunky. Had the problem for about 6 months slowly getting worse as the crack got bigger. Fitted a new lever arm and adjusted as per manual and it is now perfect.

Bazzz

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Mini Cooper S Mk 2, 1970,
Mini van 1970 with side windows now converted to 4 seater traveller

Since its after a rebuild, and gearbox work, I'm gonna be the one to say it... idler gear clearance... thinner gasket with the same washers = oh dear...

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did I tell you that I won a trophy?

Having built one once with too little clearance and got this, I agree.
2 thou clearance was not enough. Gap reduces when hot.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thanks mate, na no issue with the engine wanting to die down or stall when clutch is pressed when hot, just the gear selecting issue.

_________________
1964 MORRIS 850 - POST ZOMBIE APOCALYPSE CAFE RACER INSPIRED.

https://spotify.link/D0P4KtIP2yb

1098 +0.40
266 Kent Cam
GR Flat top pistons
HS6
1.3:1 Roller tip rockers
Stupid high CR

Thanks Simon,

Unfortunately, I am unaware of how the gearbox ran prior to the rebuild as I had purchased it along with another 1098 that had been sitting around for awhile.


Excuse my daft response, but can you please explain how the idler gear having incorrect gap would cause the gearbox to not want to select gear when hot? I would be grateful for your help in understanding this.

_________________
1964 MORRIS 850 - POST ZOMBIE APOCALYPSE CAFE RACER INSPIRED.

https://spotify.link/D0P4KtIP2yb

1098 +0.40
266 Kent Cam
GR Flat top pistons
HS6
1.3:1 Roller tip rockers
Stupid high CR

As I said above if too little idler clearance the idler gear binds when hot. Then the synchro can't give enough torque to spin the drop gears up to allow gear engagement.

Yes there are different gasket thicknesses most red ones around 33 thou and a blue one is 22 thou I bought recently. Measure old one before fitting new.

I have a heap of good sh thrust washers if you need a thinner one. New ones are expensive now.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Is it the primary gear clearance that is getting tighter when hot?
When changing gears with clutch pedal down, the primary gear isn't able to slow down but is still turning with the crankshaft.
Effectively, the clutch is not able to do its job of separating motor from gearbox.

It's usually the idler gear gets tighter as the alloy gear case expands.
Primary gear doesn't because it's steel and crank is too.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Hi, well if people are leaning towards primary gear or idler gear problems, or primary gear being touched by end of a flywheel gone on too far, then easiest way to get an idea is : Drive it to get it hot when problem happens, remove starter, get someone to depress clutch pedal, get a long shaft screwdriver and push the side edge of the clutch plate, between the flywheel and back plate. You should be able to rotate it reasonably easily. Answer ruled in or out. cheers Lindsay

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1959 Austin A40 Farina fun car
1965 Mk1 Cooper S restored
1970 Colt 1100F SS restored
2014 Mitsubishi Imiev fully electric daily driver
1948 Allard M coupe Olds 215 v8 project
1971 Twin cam Escort ex Uk championship winning rally car project