Graham_Wright
Well-Known Member
I've bought the tester and done the tests.
What figures should I expect. All cylinders seem about the same.
What figures should I expect. All cylinders seem about the same.
Last edited:
Compression testing BMC 1.5 diesel
- Thread starter Graham_Wright
- Start date
PetiteFleur
Well-Known Member
I would talk to Thornycroft who were the original sellers of these marinised BMC diesels. If they are all the same the engine is probably OK - when I did this years ago, 2 cylinders were well down which probably explained the poor starting(as well as only 2 heater plugs working) and the clouds of smoke when motoring off!
Graham_Wright
Well-Known Member
It looks like Thornycroft have (finally) disappeared. I have contacted ASAP.
Jcorstorphine
Well-Known Member
Compression ratio on 1.5 is 23:1 so ignoring the pressure rise due to heat of compression, you are looking at about 325 psi.
Graham_Wright
Well-Known Member
RichardS
N/A
I don't understand why there would be a correlation between engine size in metric units and compression pressure in imperial units?
If the compression ration is 23:1 and it starts off at atmospheric pressure, 14-odd psi, then after compression 23 times the pressure would be 14 x 23 = 322 psi.
Richard
Graham_Wright
Well-Known Member
I don't understand why there would be a correlation between engine size in metric units and compression pressure in imperial units?
If the compression ration is 23:1 and it starts off at atmospheric pressure, 14-odd psi, then after compression 23 times the pressure would be 14 x 23 = 322 psi.
Richard
I checked again last night. Maximum reading was about 240. The engine was cold and the cylinders maybe not thoroughly oiled or am I clutching at straws? The reason for checking was that it fires after a good bit of cranking on one cylinder, then slowly picks up on the others. When warm, it starts immediately.
Jcorstorphine
Well-Known Member
Did you carry out the test withh all of the injectors removed as engine has to spin pretty fast. I have tried to find the actual figure but failed. You should contact Calcut who rebuild 1.5s
Jim@sea
Well-Known Member
Even when these BMC 1.5l Diesels were new they were bad starters. In the early 1970's I was buying Austin J4 Diesel Vans which had this engine fitted and when the engines got worn (200,000 miles) they would not start without Easystart or a tow, so much so with with every J4 van I sold (perhaps 50) I gave each buyer a can of Easystart saying "You may need this" knowing that they would.
However they are reliable, when I bought my last boat it had a 2.5 BMC Diesel, I had intended to take the engine out and renew the piston rings, etc etc. but parts are virtually unobtainable. so I sold the boat.
As regards your engine if all the cylinders are the same compression that's as good as it gets. I would send the injectors off for a service and fit new Glow Plugs.
However they are reliable, when I bought my last boat it had a 2.5 BMC Diesel, I had intended to take the engine out and renew the piston rings, etc etc. but parts are virtually unobtainable. so I sold the boat.
As regards your engine if all the cylinders are the same compression that's as good as it gets. I would send the injectors off for a service and fit new Glow Plugs.
Last edited:
RichardS
N/A
That sounds very healthy for the petrol engines I'm used to .... but I suspect that for a diesel engine a reading of 240 on all cylinders is on the low side provided the engine is spinning freely and there is no compression on the other cylinders. You could add a teaspoon of oil to a cylinder and try again. If the figure goes up to 300 psi or above on all cylinders then I suspect that the bores/rings are worn. If the psi does not increase on any cylinder with the oil then it could be leaking valves but it would be more unlikely that they would all be leaking to exactly the same degree.
Richard
Jim@sea
Well-Known Member
If you are unhappy with the compressions you could do what engine tuners do, take the head off and have it skimmed, that would increase compression, you could also do a de-coke and re-grind the valves in.
Graham_Wright
Well-Known Member
Yes. Battery's good. I'll try Calcut.
essexboy
Well-Known Member
the usual 1,5 fix was to remove the heater plugs, crank the engine and see if you feel windy poo coming from each heater hole. they had a bad habit of blocking, so all the heters were doing was trying to heat a plug of carbon ! If they are blocked, a 3mm (IIRC) welded to a length of rod with a T handle to ream them out worked wonders. remember to check the heater plugs work before refitting them. I never bothered to grease the drill as the small amount of carbom going down the hole never seemed to do any harm.
Graham_Wright
Well-Known Member
I didn't know if I was happy or not as I didn't know what the readings should be which is why I asked the question.
I contacted Calcutt (who do reconditioning) who advise that a reading around 400 should be achieved with a cold engine and 280 when hot.
It seems my engine figures are down.
Jcorstorphine
Well-Known Member
I had a 1.5 many years ago which came out of a J4 van so was pretty long in the tooth when I got it but I just put on the Marinizing bits and was ok to start with but a bit slow to start.. Eventually I pulled the engine out of the boat and did a partial overhaul which was to regrind the valves, new bearings and new rings with a quick hone of the bores. Was better but still a bit slow to start as needed over 30 sec on the glow plugs.
One thing which puzzles me about your engine is that it starts on one cylinder. As all your pressures are similar, it would suggest you may have faulty glow plugs or a couple of gunged up injectors or both. One point about the glow plugs is that (I was told but not experienced) glow plugs can look ok in terms of continuity but have actually an internal short so they look ok on a meter but don't actually get hot. Best test is to pull them and see if they actually glow. Better still bang in a new set at £25 of ebay.
One other way of getting an old engine to start is to fit a "Thermostart" as fitted to Perkins 4108 etc. This is a unit fitted into the intake manifold which vaporises a small guantity of diesel to help the engine fire. Needs a bit of plumbing and possibly a small tank of about a litre to gravity feed the Thermostart.
Best of luck.
Graham_Wright
Well-Known Member
This was the original advice from Calcutt;-
Start with a good cranking speed,(good battery and Starter Motor), Have injectors Checked as CAV 5333102 with correct nozzles, and probably most important,examin each glow plug for brightish orange glow and clean glow plug port out with 11/64" twist drill so that each channel is carbon free, check voltage at glow plugs (last plug) is over 11V whilst in operation i9f not improve the wiring quality allow for up to a full minute in sub-zero temps and 30 secs even on warm days for first start."
I guess that has been derived from years of experience.
The glow plugs are new (but I will clean the holes) and so is the wiring to them. There are correct voltage readings on all of them but it doesn't prove they are working. A current monitor would be good but where do you stop!
I'll re-assemble everything, give it 30 seconds pre-heat and full throttle (which I haven't been doing).
Then report back.
The first trip in the water will be a short hop across one of the "more interesting" upper stretches of the Bristol Channel.
Not a good place to lose power!
Last edited:
Pasarell
Well-Known Member
I sold my boat with a 41 year old T90 last year and deleted all the manuals only a couple of weeks ago. Mine was very reliable but always needed lots of pre heat to start. Even in the summer 30 seconds and full throttle, but it always started after that since I replaced the glow plugs about 5 years ago.
ASAP are very good for most things but Lancing Marine are real experts on this engine and have a good stock of parts. Mike (the owner?) was invaluable to talk to.
Engine was running sweetly and pretty much smoke free when she disappeared with new owners last year.
ASAP are very good for most things but Lancing Marine are real experts on this engine and have a good stock of parts. Mike (the owner?) was invaluable to talk to.
Engine was running sweetly and pretty much smoke free when she disappeared with new owners last year.
maxi77
Well-Known Member
The best tonic I found for a 1.5 was 24 hours at 70-80% power starting became much better and after a few runs like that it started with a touch of throttle and no preheat if it had been used recently otherwise 10 seconds heat and half throttle. A good starter battery makes a big difference and regular dosing with radflush keeps the temperature comfortable.