cooked BMC1500D

[Strela]

Following overheating incidents (failing sea water pump) have skimmed head &done valves but comp still v.poor. Bores are+.060 & very good.
Have set new rings but comps are all same & oil rings all same There is no
"top" mark on any.Can your experienced rebuilders tell me are my comp rings more likely stuck or broken & will these "no differ" rings be OK?
Oil control is good. Regards Strela

 

[NickRobinson]

We need more information- have you been able to run it since the skim was done?

If not, why should the rings in vg bores be stuck/damaged?

If its never run since the skim- was the grade of head gasket too thick?

When your comp test was done, did you try injecting oil to temporarily seal the rings and if so was the second set of readings higher? (if trying this, turn the engine by hand/bar first to avoid damaging hydraulic lock)

 

[Strela]

Yes have run it since head skim. There was v.poor comp so I put oil into
2 bores & started/ran it. After warming up stopped it & found comp.
gone again. Restarted several times using same method & either quickstart or flame. Between runs & over several days injected copious
WD40 in hope of "unstick" but to no avail. Now much later have decided to meet he vast effort of engine removal & have acquired rings & gaskets. Now worried about my replacement rings & whether I will find piston damage (look OK on top) This is where previous examples can help. Regards Strela

 

[Mrnotming]

What about the bores themselves?,have they been re-honed,as distinct from re- bored?

 

[macnorton]

The rings could be gummed in or broken after overheating, you could wipe oil on the inside of the bores and turn the engine over to see what happens but I think they have to come out and be replaced.

Clean the bore with wet-n-dry using engine oil to give the new rings a bite, I would avoid using a de-glaze tool as at + 60 you have no " plan B" if you go too far with it.

I have done a couple of B series engines with the same problem and had good results..

 

[Mrnotming]

Following overheating incidents (failing sea water pump) have skimmed head &done valves but comp still v.poor. Bores are+.060 & very good.
Have set new rings but comps are all same & oil rings all same There is no
"top" mark on any.Can your experienced rebuilders tell me are my comp rings more likely stuck or broken & will these "no differ" rings be OK?
Oil control is good. Regards Strela

Compression has to escape either through bypassing the rings,bypassing the valves,or via a crack in the head,or lastly,via the head gasket.
note valves are done? Yourself or machine shop?
Lastly,the block can also have a warp,unusual but possible.

 

[macnorton]

Compression has to escape either through bypassing the rings,bypassing the valves,or via a crack in the head,or lastly,via the head gasket.
note valves are done? Yourself or machine shop?
Lastly,the block can also have a warp,unusual but possible.

As I read it oil in the bores raises the compression so its the rings. See my comment on page three of the other bmc 1500 problem topic..

 

[Strela]

My thanks to all you guys.This had a rebore not many engine hours previously. Have tried Redex while running but no joy. It looks like an inevitable rering job which leaves the question of whether my new rings are really kosher there being no "differs" I know that my old oil rings are performing well so could limit replacement to compression rings only. Valves & head skim done in same workshop.Regards Strela

 

[Bobobolinsky]

Not a nice thought, but if the engine is coming out, stepped sleeving maybe inevitable

 

[30boat]

I don't understand.I wish you didn't abreviate the words.Did you fit new rings prior to the overheating incidents or after?Are you saying the compression rings don't have the usual top mark?Have you honed the bores and set the rings end gap?Have you checked that the compression rings are straight and not tapered?Were the bores still within usable specification after honing?.Have you checked the bore roundness Ie.are they ovalized?
Since you've skimmed the head and done the valves the problem must lie with the pistons/rings/bores.

 

[Strela]

Hi 30boat. To clarify engine bored +.060 and fitted new rings & pistons before I purchased. For me it ran perfectly & at less than 100 hours began overheating at full throttle. This was start of sea pump progressive failure. Backed off from full throttle it was OK for continuous use.Unfortunately a disobient crew then cooked it on a long delivery trip. After that I removed the head,had it ground & valves done. Checked bores (no wear & no scores) & replaced head. Still no compression despite various efforts to rectify. Now decided to replace rings hopefully in late summer. New rings have no top marks& there are no tapered ones.Queries at this point in time. Regards Strela

 

[maxi77]

Some thoughts from an ex bmc1500 owner. Overheating could well be as much caused by blocking of the engine waterways. Many engines of that period needed an annual application of radflush to keep the waterways clear. Also before doing anything more I would have the valves and valve seats checked, there may well be ne valves fitted but were the valve seats checked properly and the new valves properly ground in. Unless the engine seized I would not have expected a piston and ring problem to occur.

My gut feeling is that something to do with the head work is the cause. Also was it a diesel head gasket or a petrol one that was fitted, as they are different.

For sources of parts or info there are some good canal and tractor sites as this engine in various guises was quite widely used.

 

[30boat]

Hi 30boat. To clarify engine bored +.060 and fitted new rings & pistons before I purchased. For me it ran perfectly & at less than 100 hours began overheating at full throttle. This was start of sea pump progressive failure. Backed off from full throttle it was OK for continuous use.Unfortunately a disobient crew then cooked it on a long delivery trip. After that I removed the head,had it ground & valves done. Checked bores (no wear & no scores) & replaced head. Still no compression despite various efforts to rectify. Now decided to replace rings hopefully in late summer. New rings have no top marks& there are no tapered ones.Queries at this point in time. Regards Strela

Ok.as I see it if you give the bores a light honing and the rings can be set with in spec end gaps and the ovality of the bores is also in spec that bit should be good.On to the head.have you tested the valve seats to valve gastightness?The interference fit between valve seats and the head? Were the seats recut or lapped in?This is very important because the valves must sit absolutely square in the seats.In cases when the seats have been severely undercut (or the valves overly lapped in)the correct valve clearances may beome impossible to obtain making them not sit properly and thus making compression impossible.the solution in these cases is new seats and valves,not too expensive.Apart from that I can only think of a badly warped head (which I think is not the case here) or cracks in the casting at the combustion chambers that would be evident by the pressurisation of the cooling system.It is not impossible that the block itself is out of true but being a massive casting it usually resists warping so I wouldn't worry to much about that.But check it anyway with a straight edge.The rings,having no marks are normal paralel ones.I believe you can find tapered ones which help the bedding process making it faster and more efficient.
All in all this should be very easy to solve.These are simple engines.

 

[Strela]

Hi Maxi77&30ft boat Thanks for the input. Overheating was cured by sea pump replacement & ring failure was "proved" by
lube oil injection into cylinders so I am as certain as I can be about cause & failure so thats why I am facing the dreaded engine lift out to fit new rings. I was hoping for some wisdom on stuck rings also ring patterns in this engine and recommended ring gaps. All the rest is good information but this is the area where my future effort lies. Regards Strela

 

[Aardee]

Given these are common engines with a thousand different applications, at what point is it better to replace rather than repair?

 

[30boat]

I don't think you have gummed up rings ,that usually happens when the engine has been working with loose tolerances(wear) for a long time.
You can download the manual here.It'll have all the information you need.
http://pt.scribd.com/archive/plans?...ad_promo","logged_in":false,"platform":"web"}

 

[CAPTAIN FANTASTIC]

Also, if the engine was badly overheated, and the rings have been broken, there is a big possibility that the grooves for the piston rings have been damaged/enlarged. Check for the correct clearance or, the new rings will have too much play and likely to break.