Help with gearbox

petehitch

petehitch

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I posted this on Practical Boat and received no replies, can anyone help.
It is a classic boat.
I have a Self Changing Gears gearbox driven by a Gardner 6lxb. Has anyone any advice as to how to adjust so that it does not turn when in neutral.
It always used to turn but a quick blast in astern would stop it. Now it is turning constantly.
Any advice would be appreciated.
 
petehitch said:
I posted this on Practical Boat and received no replies, can anyone help.
It is a classic boat.
I have a Self Changing Gears gearbox driven by a Gardner 6lxb. Has anyone any advice as to how to adjust so that it does not turn when in neutral.
It always used to turn but a quick blast in astern would stop it. Now it is turning constantly.
Any advice would be appreciated.
Click to expand...


Whose gearbox?????? Is it Wilson type epicyclic??? If so have you been fiddling with the band adjusters or anything else as usually things loosen off with wear.


Is it like this one???

http://lh6.ggpht.com/_07Yx7CLTxuA/Sy4BbmE9ZsI/AAAAAAAAA-U/NPafRMw0Gt8/s640/DSCF2543.JPG

This looks like hydraulic selection... Leaking control valves could cause a problem like yours.
 
Last edited:
Bilgediver,

SCG marine boxes owed nothing to to Wilson stuff, very similar to Twin Disc in operation.

Sadly supprt has evaporated like most things manufactured in UK.
 
If it is an epicyclic gearbox, and it looks as though it may be, the brake band theat holds the epicylic gear housing in neutral has worn. This allows the planetary gear housing to rotate and provide forward drive. I had a Parsons that did this, straight from forward to reverse with no neutral. Made manoevering quite interesting! If you used the wrong oil, or a friction modifier has been used, the brake band will slip too. It may be possible to adjust it but usually repalcement is the only option.
 
I appreciate the advice given, but what exactly can I do. If it is hydraulic valves leaking, how does one fix it. If it is the band need adjusting how do you do it.

Many thanks
 
Please do not take my comments as too negative, however this is the price you pay for running a boat with 40 year old transmission, no manuals, service contacts, or even a clue as to transmission model.

Rant over, likely you have SCG MRF 350.

Principal of hydraulic epicyclic gear box is that they are self adjusting, so you need somebody with the knowledge.

#1 Get a manual, several for sale on the internet (Agrispares?).
#2 Google SCG MRF, there was an outfit in Warwick who overhauled MRF's, ex SCG people I think.
#3 Twin Disc ended up with the pass the parcel, Leyland to Cummins, then to Alvis, then on to Twin Disc. Marine & Industrial Transmissions Ltd Queenborough Shipyard Queenborough Kent, ME11 5EE United Kingdom Tel: 44 (0)1795 580808 are UK Agents for Twin Disc. I do not hold MIT in high regard, however IF you get though to the right person (Martin), they may be able to point you in the direction of the guys in Warwick who are also TD service agents, or they may have other suggestions.
#4 Just a wild card Volvo Penta MAY be an option. Volvo offered SCG MRF as option alongside TD on the back of the Volvo TD122 at one time, I know that they still had good parts support until not too long ago. Never know you may find a local VP dealer who has a service guy with long memory and some old manuals.

Once you have the infomation add it to the ships papers, may make a big difference when trying to sell boat in the future.
 
Last edited:
petehitch said:
I appreciate the advice given, but what exactly can I do. If it is hydraulic valves leaking, how does one fix it. If it is the band need adjusting how do you do it.

Many thanks
Click to expand...

I suspect as said earlier it could be control valves. I did also suggestr Wilson derivative LoL.... In the Wilson marine box there are two planetary gear assemeblies . Ahead and Astern. These are selected by hydraulic actuation of the brake bands on the OD of the planetary drums. I am welsh so we do things backwards....In my Wilson the brake bands go ON to select and when released the box is in neutral. Think London ROutemaster and you might find a knowledgable fella .Same type of box but 3 forward. plus reverse.

What I suspect is happeneing is that the control valve has a wee leak in the port for ahead selection and it is allowing enough oil to pass to lightly apply the planetary brake for turning ahead. I suspect the control valve is close to or connected to the link you move with your gear selector.

A good hydraulic engineer should be able to get it out and maybe sort it . I suspect the oil feed to the selector valve is the pipe at the top of the box however I would need more info on where the oil supply comes from and what else is in the path of those hoses....IE is the supply from the engine oil pressure and is there a return to the engine or is it just gearbox supply and circulating via a heat exchanger on the engine.

Does the oil look clear and good????

There was another thread on this type of box some time back..I think the link is earlier in this thread and there were contact details given .
 
Last edited:
Bilgediver,

I agree, but what you and I are saying is RTFM (Read the F%"*&$G Manual) exept he does not have one....Yet

You repair Wilson boxes in Routemasters, I oversaw ripping them out and fitting Allison.
 
If you didn't know what type it was how did you decide what oil it needs?
Before doing anything expensive I would try simply draining the oil and putting in new, of the correct kind if you can find out what that is.

I know nothing about this box, but I do know from experience with car overdrives (similar hydraulic epicyclic operation) that they behave completely differently with different oils.
I had one that was sluggish and slipped under power running on ATF, but became like new when I changed to 80/90 gear oil.

FWIW I recall a brand new Parsons box in about 1964 which always rotated slowly ahead in neutral. "They all do that".
 
There should be a small adjuster vise (purge valve) on (beneath) the selector
(the cylindrical valve with the selector on it) screw this in or out .
This regulates the oil pressure on the 2 clutches. Not sure but when in neutral there has to be some back pressure on the clutch preventing it from dragging. Always check Engage and then go to neutral .Make the adjustment when oil is warm and engine is not idling to fast. Do not now if it depends on the type of scg but think this has to be SAE 30

regards ,
Werner
 
Thank you all for your replies. The gearbox is an MRF500HD and is a reconditioned box about 10yrs old. The oil is clean and I have always used engine oil as reccommended by the supplier.
I will investigate the cause further following your advice.
Many thanks
 
Thank you all for your replies. The gearbox is an MRF500HDMk3 and is a reconditioned box about 10yrs old. The oil is clean and I have always used engine oil as reccommended by the supplier.
I will investigate the cause further following your advice.
Many thanks
 
forgot the most obvious to check first ...there must be a smal notch on the selector valve marking the neutral position.
regards
Werner
 
wernhuy said:
There should be a small adjuster vise (purge valve) on (beneath) the selector
(the cylindrical valve with the selector on it) screw this in or out .
This regulates the oil pressure on the 2 clutches. Not sure but when in neutral there has to be some back pressure on the clutch preventing it from dragging. Always check Engage and then go to neutral .Make the adjustment when oil is warm and engine is not idling to fast. Do not now if it depends on the type of scg but think this has to be SAE 30

regards ,
Werner
Click to expand...

This is certainly worth the OP checking if he can....Are there pressure readout points to connect gauges or is it a case of tweek and see???


British rail could never get these adjustments right in the AEC engines and transmissions on multiple unit trains which sounded drastic when going from 1st to 2 nd.
 
Thanks again. I will try tweaking as werner suggests. The oil is self contained in the box and has its own cooler. The pipe on top, at the end of the control selection goes to the oil cooler. The pipe from the cooler goes back to a junction with another pipe that returns to the bottom of the box. Bilge diver thank you for your advice.
 
petehitch said:
Thanks again. I will try tweaking as werner suggests. The oil is self contained in the box and has its own cooler. The pipe on top, at the end of the control selection goes to the oil cooler. The pipe from the cooler goes back to a junction with another pipe that returns to the bottom of the box. Bilge diver thank you for your advice.
Click to expand...

Im sure that it is something minor such as an adjustment..This old equipment was designed for the rough and tumble of work boats and small naval vessels so in your care it is leading a sedentary life and should last for ages.
 
Outcome of gearbox

Could not find adjustment, maybe different type. But found address of supplier in ships docs.
Phoned Graham Knight of GB Marine 01827 718350 who was most helpful and could identify the box from unit no. He says it is the neutral brake band worn and the box needs to be dismantled to replace. But does the box no harm to use. I will run it until the end of the season then take it back to him.
Many thanks for all your help and advice, will now source a manual.
Regards
 
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