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John-T
John-T

Posted: Fri Sep 17, 2010 8:58pm

Post Subject: Lister LH150 gearbox problem

We have a Lister SR2 engine driving our boat through an LH150 gearbox. As we increase the engine speed the propeller shaft speeds up as expected up to a certain speed. If we increase the engine speed beyond that the propeller shaft slows down as if the clutch was slipping. This happens when driving in both forward and reverse. Do you have any ideas what is causing this? John

Tony-B
Tony-B

Posted: Sat Sep 18, 2010 8:15am

Post Subject: Lister LH150 gearbox problem

I think it is a slipping ahead clutch and on that box it may be a simple matter to resolve. There is an adjustment for both the ahead clutch and the reverse brake band. The instructions are in the manual which you can download from a Dutch site that has copies of manuals. Go onto my website and scroll down the first page. There is a link to the Dutch site close to the bottom. (www.TB-Training.co.uk). The manual may say use a special gauge for a gap but I think a 10p piece will do (I know a florin was about right!)

John-T
John-T

Posted: Sun Sep 19, 2010 11:48am

Post Subject: Lister LH150 gearbox problem

Thanks, Tony, that seems to have sorted the problem. I just hope that the 10p piece stays stays harmlessly out of the way in the bottom of the gearbox. Why is it that it was difficult to pull out upwards (it seemed to catch on the rim of the coin) but happily dropped out downwards when it slipped out of my grip?! I am a bit puzzled about why this worked as the gap was considerably too large. I would have thought that this would result in difficulty getting out of forward drive rather than the clutch slipping. Maybe it was also to do with removing the gunge that we found in the oil-ways. I think I was wrong about the problem happening when in reverse, it is just that the output is geared down in reverse anyway. Any ideas where I could get more information from about this gearbox, like a hydraulic circuit or a diagram of the gears? It is difficult to make out from the information and section in the manual. John

Tony-B
Tony-B

Posted: Sun Sep 19, 2010 5:38pm

Post Subject: Lister LH150 gearbox problem

don't shout too loud because slack ahead clutch springs and also a worn/lose circlip on the ahead cone can cause slipping in ahead. Marine Engine Services of Uxbridge should be able to sell you an up to date manual and any parts you need BUT I doubt the diagrams will be any better than the one I pointed you to. Your box is "strange" in that it uses oil pressure to give you neutral and reverse. No oil pressure locks the box into ahead so unless the gunge was preventing the ahead piston dumping oil pressure I can not see why either the adjustment or cleaning the oil ways would help. As the ahead clutch wears the gap reduces - not get larger and I was expecting you to find no gap. From distant memory there is a strainer over the oil pump which is low down in the box so if you did find a lot of gunge it might be an idea to add some engine flush additive to the box (not flushing oil) and run it in ahead, neutral & astern for 10 minutes each time for (say) an hour and the drain the box and refill with EP80 gear oil. The same goes into the reduction box that is probably mounted on the end of the gearbox. When you looked down into the box you should have seen a big drum with a brake band around it and a cone clutch at the back end. The shaft that appears to run right through the box is, in fact, split so the input end can rotate independently to the output end. In ahead the cone clutch springs jambs the drum and the two halves of the shaft together giving ahead. In neutral oil pressure releases the cone clutch so the input can revolves without the output turning. In astern oil pressure applied the brake band to the drum, locking it. There is a sun gear attached to the input shaft and planet gears fitted to the drum. The action of these gears with the drum locked gives you astern. The oil pump supplies oil to a rotary spool valve. In ahead the oil is directed back into the case so the springs engage the cone clutch. In neutral the valve directs oil to the ahead piston which disengages the cone clutch leaving the drum etc. free to spin. In astern the valve also supplies oil to lock the drum as well a should the ahead clutch disengaged. Tony Brooks. PS thanks for letting us know how you got on.

John-T
John-T

Posted: Sun Sep 19, 2010 7:26pm

Post Subject: Lister LH150 gearbox problem

Thanks, Tony, that makes a lot of sense. I thought it was an epicyclic but I could not get my head round it until I had your explanation. So the sun wheel and the drive cone are on the input shaft and the planet carrier is on the drum. The driven cone and the annulus are, presumably, on the output shaft though I cannot see the annulus on the section in the manual. In forward drive effectively the whole epicyclic is locked and all of it, including the planet carrier/drum, rotates at input shaft speed because the cone clutch locks the annulus to the sun wheel. I found www.mekanizmalar.com/transmission.html which has a nice animation of an epicyclic gear. I am wondering if the problem that we were having might have been due to the clutch not disengaging sufficiently in neutral and allowing some sort of contamination to remain between the surfaces. With regard to the hydraulics, I presume that the pump is a constant displacement one. Do you know if the system has some sort of unloading valve to dump the output of the pump at low pressure when the rest of the system is up to pressure and no flow is required (i.e. most of the time)? Or does it rely on pressure relief valves with, presumably, a low output flow to avoid overheating?

Tony-B
Tony-B

Posted: Mon Sep 20, 2010 7:57am

Post Subject: Lister LH150 gearbox problem

The oil pump is, I think, a bi-rotor/Holbern Eaton type oil pump as used in many engines. I see no reason why a gear type pump should not be used instead. I think there must be a PRV but I can not remember much about it because the hydraulics are so reliable. This is why I referred you to the company in Uxbridge to see if they can supply a manual. The gears are NOT epicyclics as such, there is no annulus. The input shaft is more accurately described as an input gear with a spigot bearing in the centre to support the front of the output shaft. The input gear is the sun gear with two or three pairs of sun gears (one gear in each pair being a reverse idler type gear)mounted in the drum. One of each pair meshes with the input gear and the other with an output gear on the output shaft. The ahead cone clutch is splined to the output shaft (I think from 40 years ago). The ahead cone clutch locks the output shaft to the drum which in effect locks everything else up so the whole of the inside revolves as a single unit. In astern the cone clutch is released (by oil pressure) and the drum locked. This allows the input gear to turn the planet wheels that in turn, via the idlers pairs, turn the output gear and shaft in the reverse direction. Neutral has the brake band released and oil pressure holding the cone clutch released. When in ahead the spool valve simply dumps all the pump output back into the body of the box with springs only applying the ahead clutch. If there is a clearance on the ahead piston rod then any slipping in ahead is normally worn springs, a circlip fallen off, or worn clutch linings. If the spool valve leaked allowing oil to the ahead clutch piston or if a blockage prevented oil returning from the piston then that could also cause slipping in ahead, but I have never come across either. Slipping in astern could be maladjustment of the brake band,low oil pressure or a worn/broken brake band. As all the friction surfaces work covered in oil I can not see your thoughts about contamination being correct, but I am always willing to learn. Tony Brooks. PS This is getting far too technical for the forum so either contact Marine Engine Services for a manual or email me directly but I do not at present have time to draw diagram for you.

John-T
John-T

Posted: Mon Sep 20, 2010 9:04pm

Post Subject: Lister LH150 gearbox problem

OK, thanks a lot, this has been very helpful. I think I have as much information as I need now. I am in touch with Marine Engine Services. John

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