Gearbox Problems

[Guest]

I have an PRM 140 gearbox that does not drive the prop properly when it gets hot. I'm getting 2 knots no matter what engine revs. Its ok when cold ( 4 knots) so I can still get in and out of the harbour. I'm told it will soon die so time to do the hard yards and replace.

Engine is Isuzu 23 hp and it runs really well.

I also have a Isuzu spare engine in the shed and it has a kanzaki kokyukoki kbw10 gearbox which seems to be ok , well at least not noisy when I rotate it and gear selects easily. Its also about the same ratio, that is 2:1.14.

I don't know much about this brand so wondering if they are ok to replace the prm or am I better off fixing the old box. I tried a google search and seems Yanmar use these on some models which is encouraging but not a lot of info on these.

[broadoak 0]

The Isuzu 23hp runs well with the TMC 30 Techno drive gearbox. That set-up was on our Cav 36' when the previous owners did a circumnavigation. Try Moon Engineering in Auckland, they were really helpful. We up-graded to a TMC 40 when we re-powered to a 32hp Isuzu. The TMC 40 cost us around $2000.

Hope that's some help.

[wheels 543]

Yes they are a good box. Very reliable. The big question is will it fit in place of the PRM with not to many issues of matting up to the shaft. Measure the distance from backplate to Shaft coupling and check it is the same as the PRM. Longer could be solved by cutting the shaft to suit. Shorter could be solved by an adaptor. But the real biggy would be if the centres are the same and the angle of the shaft.

Sounds like the PRM's clutch plates are worn. You could get away with just replacing them, but it would have clocked up some hrs and a complete do up would be better if you are thinking of tiki Touring with it and want it real reliable.

[Guest]

Thanks Broadoak, I talked to James at Moon Engineering and he has PRM reconditioned gearboxes for about $2500. Just a bit more than I want to spend on her at this stage.

Thanks Allan, yeh I'll check that tomorrow. Good to know they are a good box. Angles look the same, just rear ends 90 degrees off the horizontal plane. It looks somewhat smaller than the PRM.

Does the Kanzaki need water cooling? Do you know if they need to be put in reverse when sailing or left in neutral? I'm guessing these are mechanical gearboxes.

[B00B00 310]

While we are on the subject of gearboxes, my one seems to take a while to engage, in other words you need to give it a bit of revs to get the prop spining then you can throttle back. Any ideas if this is a major problem or just something that can be adjusted. I don't know what gear box it is but its a yanmar 2GM20 engine.

[ab1974 1]

It isn't a slipping gear selector cable is it B00B00? Mine was doing exactly that and turned out to be the cable that needed adjusting.

 

I would rev the motor and it would eventually select forward or reverse. Once it got interesting putting the boat back into the berth I finally got someone with their head next to the gearbox and it was clear the cable was the issue.

[B00B00 310]

Ah yes, it could well be. That's good advice thanks.

[wheels 543]

Does the Kanzaki need water cooling? Do you know if they need to be put in reverse when sailing or left in neutral? I'm guessing these are mechanical gearboxes.

Water cooling is really only needed for large HP and hard work. If underway, you can not hold your hand on the box, then you need to fit cooling. I doubt your engine would be big enough to worry it. As for free wheeliong, that is for any box that has friction plates that need to be bathed in oil. Most modern boxes are OK and I really only know of a one that has to be left running all the time. Most of the few that need to be spun, only need it every few hrs. I have a list of which need what burried somewhere, but I listed in on Cruisers Forum several years ago in the tech Forum.

[Guest]

Thanks Alan, i'll try to dig it up at cruisers forums. I can't see any fittings on the kbw10 for cooling so must be ok as is.

[PaulR 3]

40+ years ago, when using a spinning prop shaft to generate power & refrigeration, gearbox lubrication was a big issue.

 

Most gearboxes are lubricated by the input shaft from the engine moving oil around, working on the basis that most gearboxes are engaged when the motor is running, seldom idle and generally turn off when not required. This applies to most situations, trucks etc EXCEPT for buses stopped outside cafes with street seating

 

The PRM gearbox (I think but you will need to carefully check models and possibly other brands) had the oil moved around by the OUTPUT shaft, so that when the shaft was spinning under sail, the gearbox was still being lubricated and cooled. Just what we wanted in this situation.

 

A lot of yachts put the gearbox into reverse when sailing to stop the shaft spinning, and racing yachts also align the shaft so folding blades stay together to minimise drag. Once upon a time, it was a job to dive overboard and put a rubber band around the folding blades before racing.

 

Remember that it is often hard to start an engine with the gearbox in reverse. I have tried many times and sometimes succeeded

 

Some people have used shaft breaks to stop a shaft spinning. Electromechanical that unlock when the ignition is on are better, but sometimes fail when a diesel ignition is turned off but the motor is still running.

 

A physical shaft lock works well, as long as you remember to remove it EVERY time. We had one customer with a 46ft yacht that made a lock using two blocks of teak with a wing nut tightening system. We warned him against this. One day he forgot and the heat generated by the spinning shaft in the teak, wore down / melted away the shaft from 1.5" (or 2" I forget) down to about the size of a HB pencil. We had to sail the "motorless" yacht along the South Coast of the UK back to Emsworth where we replaced the shaft.

 

Yes, the above is an aside but some of the above may be helpful.

[Guest]

Thanks PaulR, good to get any info on these as I'm a bit of a novice with gearboxes. They always used to be unnoticed but this PRM is about 30 years old so might just be time to overhaul it. We have a Peugeot 405 diesel and the box on that is making noises too.

I measured the "gap" and the kbw10 is 65mm shorter than the PRM. I guess the best way to find out if the alignment is correct is to check the figures on the manuals but I've only the PRM manual, can't find one for the kbw10 online.

I could pull the prm out and then see if the kbw10 aligns by the suck it and see method.

The kbw10 seems a much simpler setup though and that appeals to me.

[Guest]

I've been studying the manual and I think I can change the reverse clutch for the forward version. That will solve my problem as i prefer to go forwards Around $500 for a new clutch kit. The driven shaft and the layshaft, with a clutch on each, can be removed with the box in place. I just hope the smoke don't get out when I remove the top.

[wheels 543]

Well really, you should fit the Kit. But if you don't have the dish, then you don't have the dosh. Can you get the clutch plates on their own?? That would save a little.

But you do really need to have a reliable box and a Kit would be the best.

[Guest]

Just had her out on the hard for a paint job both bottom and topsides plus a few other things so the boat budget is shot at the moment. My brother is an hydraulic fitter and he's going to recondition the whole box for me early next year. Thought this "swap" would at least give me good forward drive and stop the box overheating. Reverse only slows me down anyway. The "reverse " clutch should be almost new as its not often used. I will see if I can get the forward clutch plates reconditioned. I'm more the sailer than a motorist, mainly just use the motor to get in and out of the harbour but it would be good to be able to motor for a bit more than half an hour before it gives up the ghost. Balaena Bay sails sweetly even at 2 knots and I enjoy the challenge of light air sailing.

[wheels 543]

What oil is in it and is it at the absolute correct level??

The correct way of checking the oil level by using the dipstick is:

Ensure that the gearbox is in neutral.

Run the engine and gearbox to ensure that there is oil in the cooling circuit.

Switch off, then remove and wipe the dipstick.

Screw the dipstick fully down, then remove it and read the oil level.

Top up with an oil to the maximum mark on the dipstick.

A 30W or 40W oil will be good, byut make sure it is a good oil, not something cheap.

Another thing to check is that the box is getting no hotter than 80deg, 90deg max. And also check that the shift lever is being pushed right forward and not just part way.

I found all my info on the box, so if there are any more questions, fire away.

[Guest]

I've just changed the oil twice, using 30w. levels are correct. It changes gears really well so the hydraulics are ok. I talked to James at Moon Engineering and he was very helpful. He seemed to think the change of clutches would help with forward motivation but suss on reverse. I'll try the change of clutches and maybe replace some bearings and seals as needed. Does not sound too difficult to remove the shafts, happily the box can stay in place.

I don't have a temp guage for the gearbox but I'm pretty sure its overheating due to the clutch slipping. Water flow to the heat exhanger is ok. I checked the throw of the lever and seems good. I wonder if the clutch plates can get new stuff bonded onto them.

I guess reversing for a while to see if the clutch starts slipping may be one way to test it. Luckily she's a double ender so won't look funny at all

[wheels 543]

Or just pull against the lines on the dock.

Yeah it's the slipping that creats the heat and the plates will be worn.

Overfilling these boxes can cause heat and of course the heat also can cause problems. Poor oil can cause slipping as well. But I think the box is beyond all that and is just simply worn out. You could replace the forward plates and nothing else and take a risk all the other stuff is OK of course. If you don't have oil leaks and don't have bearing noises, then it could be worth a shot. The main reason why a "Kit" is usually done is that the parts are usually cheaper than the labour of pulling it down and so on. And they are damn heavy boxes, so removing froma boat is not always easy and only wants to be done once when you are paying for somone to do it.

You maybe able to save sustantial money by just getting the plates and then buying the Bearings and seals from a Bearing distributor and not as part of a "Kit", which can sometimes be far more expensive. Although the difference being that a "Kit" has everything you need, where as sometimes when doing it yourself, you may skip something not realising you need it.

[Guest]

Thanks kindly Alan, really appreciate the advice. I'll give it a try even though a bit nervous of the inner workings of a gearbox. These weigh about 54kg so nearly as heavy as the Admiral. She'll never be able to lift it so no way I could.

 

Good to hear that the bearings and seals are standard sizes. Not like Jap motorcycles that use bearings an half mil different so one has to use their brand at enormous cost. My Ducati uses standard bearings also.

Taken a while just to find out which model box it is. Nothing indicated on the box but after reading the manual over and over I found one cover that has 3 bolts on one model and 2 on the prm140!