Thornycroft engine stalls when f'wd or reverse gear engaged.

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rwterry

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Thornycroft engine stalls when f\'wd or reverse gear engaged.

Everything worked fine on the 40 min. motor trip to the yard for a lift out. The cutlass bearing and stuffing in the stuffing box were replaced. Prior to re-launch everything was checked over and the propshaft turned easily by hand. When back in the water the engine was started, first time as normal, f'wd engaged and the engine stalled. It stalls in reverse as well.
A mechanic in the light of no other plausible explanation diagnosed a seized gearbox. The gearbox was replaced at no small cost but the engine still stalls. The engine can be turned over in gear on the starter motor with everything revolving OK but will not start. I did manage to get it to run for a short while by starting it in reverse but with the throttle fully open it only ran at tickover speed, there were not clouds of black smoke but just some unburnt fuel on the water surface.
I replaced the mechanical fuel lift pump about a month ago and it worked fine on the trip to the lift out. I have dissasembled the pump to check the diagphram etc. which is all OK. I have checked the fuel on/off tap and that is OK.
I have loosened the bleed screw on the injection pump whilst cranking the engine and got a squirt of diesel. The air filter is clean. I have replaced the fine fuel filter.
The engine is a Thornycroft 80D ( With mechanical stop lever.)
driving a ZF Hurth HWB100-2R gearbox and Darglow feathering prop.
I have run out of ideas now so any help is greatfully received.
Regards to all,
rwt
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

If you can turn the shaft by hand, in neutral, there's nothing wrong with the stern gear. If you can turn the engine over with the gear engaged (by hand if necessary), there's nothing seized in the gearbox. This only leaves the engine. If it ticks over but stalls as soon as you engage gear, it sounds like a fuelling problem, possibly injector related, it it still ticks over but stalls as soon as you try to move off, it could be the throttle linkage......
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

check that the stop control lever is in the correct positon,moving enough on the pump,its possible the cables moved and not allowing it to open properly,i guess the same goes for the throttle,
check your glow plugs, first that they are getting power and also that they are working ,thornycrofts do not like to start unless all glowplugs are working,
if all that ok,loosen injector nuts at the injector and turn the engine over,this should bleed air out of the pump,you should get good clean dribbles/spurts, as it spurts tighten the nuts back up and engine should fire,
if you have fuel coming through and it still won't fire/run it then means digging a bit deeper,poss pump timing although if the pump has not been removed it should not have altered, before going down that route check the above as they are easy.
i can't see how starting it in gear can help,i find on mine that the increased drag of the gearbox,prop moving slows down the starter due to incresed drag,
it seems to me to be 2 seperate problems first the engine won't start , second when engaging the gearbox it stalls,my first thought on the stalling is you are overpropped and the engine has not got enough power to overcome the prop resistance,was anything changed once the boat was in the yard,specifically the propeller,if it was that is probabally your stalling problem.
good luck mike
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

I had a similar problem a couple of times with my Thornycroft ... Do you have oil in the 2nd oil compartment of your transmission - gear box? I did not even know there was a 2nd compartment - its astern of the one on the top with the dip stick..
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

Go back to basics instead of listening to well intentioned scatter gun advice, it worked then it didnt, what changed? the stuffing box etc, concentrate on this, if it stalls it is because of load on the engine, if the expensive gearbox change didnt fix what else is loading that has been changed? by the way, they did change the gearbox for sure?
Stu
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

did i misread the post skipper stu i thought it said that the engine would not start,i would assume that to remove the gearbox you have to move the engine,pipes and cables then refit themwhich leads to,rebleeding fuel systems etc etc,if the engine layout is similar to mine it has a fuel filter on the engine above the pump which would hold enough fuel for the engine to start and run for a short while. until the engine is running its hard to sort out the stalling part,i agree tho as i said in my reply that something else seems to have changed to cause extra loading
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

Just to expand a little on my post about the 2nd oil compartment in the gear box of a Thornycroft... Mine was working fine and I was on a 4 day passage across the Med. Wind dropped and I started the motor - put it in ahead and it stalled - repeated the process several times - stalled. dived on the prop - clear and sailed into a Tunisian harbour where the engineer 'fixed' the problem _ took the gearbox out quite easily and put it in the workshop - hit me for £200 put it back in and all AOK.
5-6 years later in Cambridge Maryland was re-launched - started engine - put it in ahead - stalled - repeated process - stalled. US engineer took it out and 'played' with it - no go -- tried 3 times to find fault then suggested I buy a new transmission. At this point I had a go myself with the aid of a booklet from a UK Thornycroft engineer and found the 2nd oil compartment was empty - filled it with oil - started engine - put in gear and it all worked....

The 'stalling' symptoms sound exactly same as mine... It is an easy and cheap fix if you can locate the two screw bolts to the 2nd compartment - low down on starboard side of the transmission.. you need a tube to get the oil in... worth a try I think.
Michael
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

Following on from the posts regarding a second chamber on the gear box I am baffled. The gearbox is a ZF Hurth HBW 100-2R. As I said the gearbox was replaced, by me, and topped up with ATM fluid as detailed in the owners handbook. I have the old gearbox at home and have dismantled it and can assure you there is no second chamber. It must be a different type of gearbox referred to in the other posts.
By the way there was nothing wrong with the old gearbox.
Regards to all,
rwt
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

i think michael b may have had a tmp box with the optional reduction drive fitted,the reductin drive is as he says a seperate unit with its own oil chamber.only guessing but tmp's were fitted to alot of thornycroft/bmc's i proudly have one myself
 
Re: Thornycroft engine stalls when f\'wd or reverse gear engaged.

Just a thought.A faulty (seized) regulator will allow the engine to idle but as soon as any load is applied making the revs drop ,the weights won't collapse as they should .This will prevent the increase in fuel delivery wich will in turn increase power.
 
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