15 replies to this topic

[ryan22_lgm]

Hi all ! Recently finished my mini project and have now done a few shake down runs! The car has a 1340 engine in running 10" wheels. Head is standard exhaust is full maniflow 1.75 system with hif44 carb.
The issue I'm having is it's screaming it's tits off at 60/70mph so I guessed I have the wrong final drive fitted. I have had the plugs out and marked wheel / flywheel to try and work out the final drive but something seems very wrong. Engine turns only 1.5ish times for 1 rotation of the wheel.
I bought the engine as a built up unit and have only done the top end and various oil seals. Only thing I'm thinking is the previous owner was involved in grasstrack racing so gear ratios been altered??? Engine pulls nice and strong and dosent burn oil or slip the clutch. Transmission is quite 'winey' but don't think it's enough to be straight cut drop gears causing the problem.
I have a 3.1 ratio diff final drive set I can put in but just wanted to know if it sounds like the final drive that's the problem or the gearbox. Thanks in advance guys! Got to get it sorted before castle Combe as motorway driving would kill me !

[Midas Mk1]

Any idea of revs at 70? Be able to work out the current diff ratio using guessworks calc and some playing about. 

 

My orange cooper on tens runs just over 4k at 70 with a 3.2 diff, though i've found a 3.1 to be a nicer cruiser. 

[Swift_General]

In top gear drive from the engine is 1:1 to final drive pinion (assuming standard drop gears), so if the engine is screaming away it can only be the final drive. Engone turning 1.5 times for 1 revolution of wheels doesn't sound right (and if it was possible would give the opposite to what you are experiencing!). You should be able to measure this pretty accuratly. Put the gearbox in top gear and jack 1 of the front wheels off the ground. Put a marker on the wheel, and rotate the engine by hand to turn the wheel, exactly 5 times (for example). If you had to turn the engine 10 times then the final drive ratio would be 4:1 (10 divided by 5 then doubled as only 1 wheel is turning).

Edited by Swift_General, 29 August 2017 - 08:13 PM.

[ryan22_lgm]

I can temporarily wire up a rev counter maybe..... I will try that tomorrow night !

[ryan22_lgm]

In top gear drive from the engine is 1:1 to final drive pinion (assuming standard drop gears), so if the engine is screaming away it can only be the final drive. You should be able to measure this pretty accuratly. Put the gearbox in top gear and jack 1 of the front wheels off the ground. Put a marker on the wheel, and rotate the engine by hand to turn the wheel, exactly 5 times (for example). If you had to turn the engine 10 times then the final drive ratio would be 4:1 (10 divided by 5 then doubled as only 1 wheel is turning).

This is what we did I think. Put car in 4th gear. Removed plugs and clutch inspection cover marked wheel and flywheel through cover. Turned wheel 1 full rotation and counted amount of times flywheel went over. Only took 1 and around 1/2 turns of engine for full rotation of the wheel? Seems very wrong

[Spider]

Had this discussion elsewhere just recently.

 

Most of the noise you can hear - or should be able to hear - is the cooling fan.

 

These engines rev in the range 2000 - 4500 RPM happily and are made to do so.

[ryan22_lgm]

Had this discussion elsewhere just recently.
 
Most of the noise you can hear - or should be able to hear - is the cooling fan.
 
These engines rev in the range 2000 - 4500 RPM happily and are made to do so.

This is my 3rd mini and just seems very different from the others. :/ Want to make it usable on the motorway and link roads for shows! I have a metal export fan fitted if this makes a difference. Could it be bent???

[nicklouse]

measure again with say 10 engine revs how many wheel revs do you get. will remove errors. as your numbers are off.

[ryan22_lgm]

measure again with say 10 engine revs how many wheel revs do you get. will remove errors. as your numbers are off.

Ok mate will do tomorrow after work!

[Spider]

 I have a metal export fan fitted if this makes a difference. Could it be bent???

 

 

They do make a lot more noise than the plastic fans. I like them, but I'm in a warmer / hotter climate too.

Of all the new ones I've bought in recent years, they usually, but not always run 'straight' but every one has been well off centre.

 

Swap it out for a plastic one.

[timmy850]

Mine has a 3.76 diff and at 60mph it's doing 4000rpm.

 

You can get an idea of rpm/speed/diff ratio here:

http://guess-works.com/Tech/ratio.htm

[absx2]

It`s unlikely your speedo is calibrated to your gearbox which won`t help in deciding what`s good or bad.

 

I fitted an MG Metro unit to a mid 80`s car with twin clocks behind the steering wheel it would rev a bit at 70 mph which happened to be 90 mph as the speedo was progressively 8 mph out.

 

As above Guessworks ratio calculator is excellent and he sells the worm drive and pinion gears as well. 

[Wim Fournier]

"This is what we did I think. Put car in 4th gear. Removed plugs and clutch inspection cover marked wheel and flywheel through cover. Turned wheel 1 full rotation and counted amount of times flywheel went over. Only took 1 and around 1/2 turns of engine for full rotation of the wheel? Seems very wrong"

 

Oké. And;because one wheel is turning and the other one is standing still, you have to multiply the outcome by 2 = three turns of the wheel against one turn of the crankshaft.

This means the diff is about 3 : 1.

Try ten 'full'  turns of the crankshaft and count the turns of one wheel (other wheel on the ground). Multiply by 2 and yuo get nearer the actual diff  figures.

[ryan22_lgm]

Right got the engine out today and stripped the diff out! Final drive is 3.1 19/59 teeth. Now we don't know what to check next! Is it worth checking flywheel/ clutch? Also what final drive ratio is recommended for a fast road 1340 running 10' wheels ?

[nicklouse]

perfect ratio for what you want.

 

stupid not to check the clutch as it is out.  might have been slipping.