T90 - BMC 1.5 engine problems, advice please.....

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dickh

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Moody 33 mk2 fitted with the Thornycroft T90 (BMC 1.5) diesel with a 1:1 g/box driving a 3 blade 12x9 prop. Takes a long time to start, two or three bursts of 20 seconds on the starter, clouds of blue and white smoke when started, gentle haze of smoke after about 5 minutes running. Won't rev above about 2000 RPM(a guess as the tacho isn't working) without black smoke.
Recent work done:-
1) Head removed to repair broken heater plug, new plugs fitted, head decoked, valves ground in, new valve stem oil seals fitted. All new gaskets fitted etc.
2) Fitted new thermostat rated at 82ºC - engine ran at 120ºC. Replaced with old thermostat rated at 72ºC - engine ran at 100ºC - I suspect the gauge/sender as the header tank water is not that hot - you can hold your finger in it for a few seconds. Both thermostats tested in water with Jam thermometer(don't tell SWMBO) and started to open at figures stated. Plenty of sea water thro' the heat exchanger.
3) Getting blowback from the oil filler cap.
4) Did a compression test at the weekend - 425; 330; 330 & 315 PSI - don't know what the correct figure should be, Thornycroft not answering the phone this morning.
5) Injectors tested OK before refitting head.
6) Engine reconditioned in 1997 but had minimal/no maintenance since(my view).

What is the forumites views? I think the engine is knackered and it's either another rebuild, a good secondhand engine or a new engine. The problem with a new engine is I can only swing a maximum of 12 or 13" diameter prop or I will have a groove in the hull!
 
Hi

Process of elimination:
Are you sure all wireing is correct as it sounds as though the heaters are't working when you start and the tacho should read whatever the colour of the exhaust smoke.

Do you have an air leak in an injector feed? Would account for lack of power and exhaust smoke.

Was the timing set up correctly after the head removal?

Don't throw it away...cost you £4k to get a modern equivelant.


Phil
 
Check the air inlet is not clogged first. Check the injectors are seated properly and not leaking compression. Make sure there is no air getting into the diesel system as said.

Failing that, try a another new head gasket?
 
Hi Phil, the heaters are working, the ammeter goes to 25-30 amps when in the 'heat' position. No air leak as far as I know, new injector pipes fitted. I didn't touch the timing after the head removal so assume it's OK. I do appear to have fuel seep(can't really call it a leak) from the engine mounted fuel filter, fitted new filter + gaskets, renewed all sealing washers and now assume I have a porous Mazak casting. Fuel just gathers around the base.
I do realise a new engine will cost in the region of £4½k as I will have to have a new RH prop, shaft + exhaust system.
 
I did fit a new head gasket! - the first one I fitted upside down and no oil got to the rocker shaft. No difference before and after - apart from fitting original thermostat as temp. gauge wasn't working then. Injectors should be OK - I fitted new washers etc. (but I will check) Air inlet clear(no filter fitted!)
 
what was the engine like before you had the head done ?

im curious to know its condition before you started so as i might make some suggestions as to the fault now.


steve
 
If the engine was running with no oil to the rocker shaft for any length of time, it and/or the rockers may be badly worn, which could easily account for poor performance and smoke. Wouldn't help with starting either.
 
Steve. History on the engine is sparse - I bought it in the autumn and it had been ashore for at least a year. One of the first jobs I did when ashore soon after I bought it was to start it, again it took a long time to start with lots of smoke, but did settle down after a few minuts(I did have water pumping through from a bucket & hose) - but obviously I couldn't run it under load. I changed the oil and filter, the oil was very thick and sludgy. New oil certainly appeared to help in starting. Then I discovered the broken heater plug and so I took the head off to repair.
I'v just spoken to Thornycroft who were very helpful, and suggested I use "Millers Glaze Busting Oil" and run under load for about 15hrs. Apparently this can work, with reduced oil mist and crankcase back pressure. Has anyone ever used this oil? It's the first time I've ever heard of such an oil.
 
The compression test figures look reasonably well balanced and about right aside from one which is excessively high.

This may be due to an error in taking the reading ? or oil/water in the cylinder from somewhere ?

That you haven't adjusted the timing does not of course mean that it is right. Just check it. The short run without rocker oil is not good but should not have created a problem - presumably you oiled everything as you assembled it which should have kept the rockers right for that length of time.

Check the oil pressure. If that's ok the only question left really is the state of the injectors and injector pump - do they need testing/cleaning ?

The engine having stood for a length of time would suggest piston rings being gunged up but running may have improved the situation. Air leak on the fuel supply has already been mentioned above. Indirect injection engines like these require higher compression pressures and therefore are more prone to low compresion problems causing poor combustion and a smokey exhaust.
 
I've spoken to Thornycroft since posting this query and compression on a new/reconditioned engine should be around 475 PSI. So it looks like I have low compression on three cylinders. They reckon they should start in hot weather without heat plugs. Thought the problem may be the bores need glaze busting and suggested 'Millers Glaze Busting Oil' and run it for 15 hrs under load - should improve. Oil pressure appears OK - 50 PSI when at about 1500RPM.
 
I just wonder whether you have a small air leak possibly on the lift pump side? When you reassembled everything did you use new copper washers on banjo unions etc? I suggest that you at least crack each injector pipe crank the engine a few times, tighten up, and then crank for real without glow plugs. If it starts straight away. then there is the problem.
Most "real engineers" will tell you that rebuilding the top end on a high hours engine, may result in pressure past the piston rings, resulting in the readings you are giving. Aagain the glaze busting oil must be worth a try, as it is cheaper than a replacement engine.
I replaced a 1.5 BMC with a 1.8 Ford, by getting the marinisation kit, and the bell housing adaptor, for the existing Hurth gearbox, so that the only costs were the engine, as the shaft, gearbox and prop remained the same. However the boat does 4 knots on tickover and I rarely rev above 1800 rpm - I think we can assume it is slightly "over engined"
 
sorry to see you are still having problems. you seem to have covered most things. a call/email to tony on the Reading diesel course may yield some new ideas. google reading diesel to find address
 
Hi,
I have been playing with these engines for many years, Rebuilt loads of them etc etc. From your description on the general running of the engine and the compression readings i would say that:
Iether the rings are broken or damaged
The bores are badly glazed ( Which is in my view unlikely)
Or they are gummed up.
This would acccount for the chuffing at the filler cap.
The compression gases are getting by the rings and compressing the sump. Which then has to escape via the engine breathers.
The compession readings are to low on three of the cylinders only which would generally rule out the glazing, Which would usually be on all four.
If you do use a de-glazing oil or a flushing oil be aware that it may wreck the rest of the engine which sounds o.k from your oil pressure readings.
I have used flushing oils and a number of other products and never really had a good result.
In fact some of them did more damage than good.
Hope this helps but it may be that it needs a re-bore and new pistons, Or a short block re-build.
Not an expensive job on the 1.5 bmc which is a great little engine and in my view the best one that BMC ever made.
Looked after they will last for years, But you must change the oil regular. If you don't then things turn ugly.
Joe
 
Joe,
Thanks for your input. I will probably run it for the rest of the season and see how I get on. I'm in two minds about the Glaze Busting Oil. I also agree with your view about three poor compressions not pointing to glazed bores. It looks like either a rebuild, a short engine, a good s/h engine or a new engine with all the associated new bits and pieces. I'm going to do a lot of thinking over the next few weeks.
 
from what you have added i would think that the bores are glazed up, it might be possible that previous owners have used the easystart option to aid an exsisting problem. Try what has been suggested with the oil but i feel that it wont have much effect and you may be better off just getting it honed or even rebored.


steve
 
I would just try running it for several hours, keeping an eye on water temp and oil pressure. I have had a variety of problems with mine but all seem to disappear after a good long run. I did have a black smoke problem once which took a long time to solve and was only cured when I blew out the diesel return pipe to the tank, which was blocked.
 
Re: T90 - BC 1.5 engine problems, advice please.....

Disconnected it from the fuel system and blew down it. Could not unblock whatever was in it so got an old tyre valve, put it in the end of a flexible pipe. secured with a jubiklee clip, put the other end of the pipe over the return pipe, secured with another jubilee clip and pumped with a foot pump. Cleared very quickly. Reconnected, started up and no black smoke!
 
Re: T90 - BC 1.5 engine problems, advice please.....

Any tips for getting rid of white smoke.
 
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