BMC 1500 revs up when hot??

[Chas78]

Hi All,

My BMC has started to rev up when hot its ok when cold but when up to temperature when i move throttle a bit it revs up and takes a while for the revs to drop this is quite worrying when trying to manoeuvre slowly in tight spots  i also notice the forward gear takes a while to engage where as the reverse seems instant could this just be a fault in the Morse control ie adjustment? any help or suggestions very much appreciated 

[RLWP]

What gearbox have you got?

[Chas78]

54 minutes ago, RLWP said:

What gearbox have you got?

I was told it was a prm 100 but a friend told me its not its either a 120 or 150 here are some pics 

[Bee]

I think I would try disconnecting the morse control from the g/box and the engine when the engine is hot then see if it still does funny things when you operate the gear lever and engine speed control by hand, then you will know whether its something to do with the cables etc.

[Chas78]

7 minutes ago, Bee said:

I think I would try disconnecting the morse control from the g/box and the engine when the engine is hot then see if it still does funny things when you operate the gear lever and engine speed control by hand, then you will know whether its something to do with the cables etc.

Christ why didn't i think of that  but having said that it only happens when the engine is warm not cold??

[Bee]

Maybe everything is a bit different when the oil is hot and thin?

[RLWP]

44 minutes ago, Bee said:

Maybe everything is a bit different when the oil is hot and thin?

Yes, probably what the gearbox is doing. The oil in there will be hot too

It sounds to me like either the Morse is not properly adjusted or more likely the forward clutch is slipping

Richard 

MORE. It isn't a 120 or 150. 100 sounds more likely 

Edited February 28, 2018 by RLWP

[Chas78]

1 minute ago, RLWP said:

Yes, probably what the gearbox is doing. The oil in there will be hot too

It sounds to me like either the Morse is not properly adjusted or more likely the forward clutch is slipping

Richard 

That sounds expensive 

[RLWP]

55 minutes ago, Chas78 said:

That sounds expensive 

Moderately, not massively. Certainly less than the cost of a new gearbox

So - first make sure there is oil in the gearbox, otherwise it slips through lack of pressure. Then see if the morse control is putting the lever on the gearbox right forward. And when it is right forward does the gearbox seem to slip in gear when warm?

Richard

[Tony Brooks]

I go with the low oil then think about a slipping clutch but first what oil is in there. It should be engine oil. It should NOT be ATF/Dexron.

Disconnect the cable on the gearbox lever and try it by hand just in case its a cable/adjustment problem.

I reckon its a 1970s boat so the box is probably pushing 40 or 50 years old. It is probably worth checking the hot gearbox oil pressure. If its low then its just possible the spring in the oil pressure relief valve may have weakened so adjustment may sort it - on the other hand it may not, especially if the oil pump is worn.

[RLWP]

4 minutes ago, Tony Brooks said:

I go with the low oil then think about a slipping clutch but first what oil is in there. It should be engine oil. It should NOT be ATF/Dexron.

I forgot that one! Thanks Tony

[Chas78]

Thanks for the info i will try what you have suggested i did check the oil level which was just below the line on the dip stick my boat was built in 1980 a Hancock and Lane 

[cereal tiller]

6 hours ago, Chas78 said:

Hi All,

My BMC has started to rev up when hot its ok when cold but when up to temperature when i move throttle a bit it revs up and takes a while for the revs to drop this is quite worrying when trying to manoeuvre slowly in tight spots  i also notice the forward gear takes a while to engage where as the reverse seems instant could this just be a fault in the Morse control ie adjustment? any help or suggestions very much appreciated 

An Oil change may improve things ,would be on my list of things to Eliminate before considering Overhaul.

[Tony Brooks]

1 hour ago, Chas78 said:

Thanks for the info i will try what you have suggested i did check the oil level which was just below the line on the dip stick my boat was built in 1980 a Hancock and Lane 

I might be wrong but I thought JG Meakes had gone broke by 1980. If so your engine may be second-hand.

[Chas78]

58 minutes ago, Tony Brooks said:

I might be wrong but I thought JG Meakes had gone broke by 1980. If so your engine may be second-hand.

[Chas78]

No more revving up after replacing the fuel filter and tightening the various loose and leaking hose clips thanks again all for the advice 

[LEO]

On 2/28/2018 at 19:31, Tony Brooks said:

I might be wrong but I thought JG Meakes had gone broke by 1980. If so your engine may be second-hand.

The first boat I bought had a J G Meakes Raw Water 1.5 conversion, and the invoice for that was dated 1980, coupled with an odd TMP? gearbox (Produced by a guy from Thames Ditton), it was forever stripping the grooves on the input drive.

[Tony Brooks]

4 minutes ago, LEO said:

The first boat I bought had a J G Meakes Raw Water 1.5 conversion, and the invoice for that was dated 1980, coupled with an odd TMP? gearbox (Produced by a guy from Thames Ditton), it was forever stripping the grooves on the input drive.

Those boxes also had fun with aluminium rivets on the clutch plates I recall. That's why we never touched them for the hire fleet. PRM were far more robust. I also think they used a  cooling water gallery cast into the joint between two parts of the housing instead of an oil cooler. Being an alloy case these tended to block up ove winter with white aluminium corrosion. TMP = Tideway Marine Products and a few years ago I think they were still in being.

 

[LEO]

14 minutes ago, Tony Brooks said:

Those boxes also had fun with aluminium rivets on the clutch plates I recall. That's why we never touched them for the hire fleet. PRM were far more robust. I also think they used a  cooling water gallery cast into the joint between two parts of the housing instead of an oil cooler. Being an alloy case these tended to block up ove winter with white aluminium corrosion. TMP = Tideway Marine Products and a few years ago I think they were still in being.

 

Yep. 'Orrible bits of kit, used a clutch from a BMC mini, I replaced it with a Hurth and sold the old bell-housing, gearbox and spare main shaft to a hire fleet operator on the River Avon in 1989. The BMC is as far as I know still in service.