JCB 3CII Engine seized- rebuild

[Dave-OLW]

JCB 3C II 1973 serial No. 3C 100788 Tractor serial No. 384B 172471
Engine serial No. 6797 Leyland 4/98NT I have had and used this machine since 1998.

Engine overheated, then after allowing to cool and refilling cooling system it overheated again and seized. Found there was no thermostat. Have removed engine and stripped down, it was number 2 piston big end that had seized to crank shaft.
I found the balance shaft gear was not engaged due to the allen screws had come out of the balance gear, and shaft had moved along, allen screws in sump.
I thought first of all this was part of the drive to the oil pump and this was why it had seized, but I don't think it does effect the oil pump. So did it seize due to overheating? or is there a problem to the oil supply to the shells at the N0. 2? It looked very dry and burnt, see picture, there was plenty of oil in the other big ends.
With all the pistons now removed, timing gears and injector pump still connected, I can rotate crank shaft which appears to have a stiffer part at one point, is there a problem or is this due timing gears or injector pump?
Attached photo's:-
Shells from No. 2 Big end
Dry No. 2 Big end
Balance drive shaft gear
Allen screw
N0. 2 big end after removal of con rod

[Mrsmackpaul]

welcome Dave
Sorry I cant help with answer but if it was mine I would strip it down completely youve come this far and that way you make sure nothing else is wrong
I dont think the thermostat missing would cause this but may well be wrong
Most times a thermostat is removed it is an attempt to fix a over heating problem and rarely works to solve the problem I would be looking further before being confident I had fixed it

Paul

[Jeremy Rowland]

Hi Dave and welcome to CMN like Paul has said you are best stripping the engine down after such an issue; I would think the overheating issue could be several different things if you read though similar pages on this site the problems with these engines overheating tends to stem from clogged radiator cores to missing thermostats etc.
Whatever I would have thought that the crank would at least require a polish after such a failure or more than likely a regrind, it may also be cracked which you would not so easily pick up with it in situ; just some thoughts to try and help you.

Jeremy

[Dave-OLW]

Thanks for the replies. In turning the crank over the No. 1 main bearing (which I had removed to remove oil pump to get access to big ends) upper shell and upper thrust washers have come out. It does turn now with no resistance anywhere so it was them causing stiffer part. There is no way I can get them back in, and as you suggest it would be best to strip it all down, so I have started to remove crank shaft.

David

[Dave-OLW]

Hi,
I am unable to undo the Crankshaft Nut, have 1 1/2" socket, have tried locking starter ring on flywheel, heating nut, wood blocks in block and finally tried using starter motor. Have broken two socket bars and bent another, but it still will not undo. Any suggestions how to move it?

Thanks David

[Jeremy Rowland]

Hi,
I am unable to undo the Crankshaft Nut, have 1 1/2" socket, have tried locking starter ring on flywheel, heating nut, wood blocks in block and finally tried using starter motor. Have broken two socket bars and bent another, but it still will not undo. Any suggestions how to move it?

Thanks David

David I don't know this engine so I am assuming that you are referring to the nut on the damper end of the crank as the flywheel is normally held on by several small bolts?
If the sump is off the engine you could carefully jamb the crank using a large block of wood; don't use metal you could damage the crank, then use a 1" drive bar with a hex socket (not bi-hex) and while you have the pressure on the bar get another pair of hands to give the end of the 1" bar a smack with a decent sized hammer.
My only other advice is to check the hand of the thread before you have a go in case it is a left hand thread or you would be trying to tighten it even more!

Jeremy

[philwheelton]

Its a right hand thread and sometimes very tight so a block of wood in the crank should do , when rebuilding make sure you time the balance gears up the oil pump gear has two dot's on it one to the crank gear and one to the balance gear !

[Mrsmackpaul]

big rattle gun and some heat on the bolt head
gotta use at least 3/4 drive sockets for a bolt that big you can put six feet of pipe on them and the wont break

Paul

[Dave-OLW]

Thanks, yes have ordered a 1" drive socket and bar and will try that.
Assumed it was right hand thread as manual does not say otherwise.
As regards setting the balance gears the manual shows the balance gears one with one dot and the other with two dots, but I cannot see any dots on my Balance gears. As the alien screws had come out on the one on the drive shaft I do not know how they should line up.

Thanks David

[Dave-OLW]

Hi,
I managed to undo the crankshaft nut with the 1" Drive socket and bar, plus a 8' scaffold pole, had to bolt down engine to workshop floor to stop it turning over.
It appears only the number 2 rod journal is damage from loss of oil, the rest look ok, can you just regrind one or do they all have to be done?

David