Engine blow by - Mitsubishi K4D

[Jentreefication]

Would love some advice on this issue please. Am considering buying a 37ft 1990 Colecraft cruiser narrowboat. Price is £26k. 

 

The engine is running fine at the moment, travelled from Northamptonshire to London with no issues and starts daily, running for an hour or two with no probs. 

 

What I've been told is "the engine has blow by - it breathes..which means when the pistons come up on the compression stroke if piston rings and bores are worn it blows down past rings putting pressure on the crank case and producing smoke.the worst case scenario therefore is that the engine needs to come out, be stripped down pistons re-bored and oversized pistons fitted and new gaskets and back in. Parts are available at the costs I've shown. This is not necessary right now with careful maintenance but is the worst case scenario of what may need to happen" 

 

The advice estimated from the seller is that it will cost around £3k but doesn't need to happen immediately and maybe not for some time. 

 

Various mechanics advice has been to get reconditioned engine and replace with a price range from £5k upwards. They have also said that without viewing its very difficult to know what is really going on and quote accurately. 

 

What next steps would you take if you wanted to buy a boat with this potential issue? 

 

I anticipate getting confused by conflicting advice but would appreciate input ? Thanks 

Edited February 2, 2021 by Jentreefication
Additional info

[nicknorman]

Blow by is much as you describe - combustion gasses getting past the pistons rings and pressurising the crank case, leading to excessive oil consumption and smoking.

 

But the cause might not be excessive wear, it could also be bore glazing. This is where combustion residue builds up as a kind of gum or varnish on the bores, maybe the piston rings get a bit sticky in the piston ring grooves too, all resulting in poor sealing between the pistons and the bores. This can be caused by low combustion temperature ie running the engine at a very light load (idle) for long periods and or using oil that is too “fancy” for the engine.

 

So it might just be that the bore glazing needs to be removed - this still requires the cylinder block off, but the process is just one of honing (pretty much scraping the gunge off the inside of the cylinders, rather than a rebore. Depending on how bad it is, things might even be improved just by running the engine hard (on a river, not on a canal!) for a while to get the cylinder insides really hot. I think it is called the “Italian tuneup”.

 

But of course with all that said, maybe the engine is indeed badly worn.

[roland elsdon]

The running daily for an hour may be the issue. If its to charge then the engine will never get to temperature. The rings will never fully expand and excess fuel may  even build up in the sump.

Idling a diesel under no load for periods is so bad for them.

First thing would be an oil change , air filter change and fuel filter. Then italian  decoke when it is good and hot. 
If it still smokes compression test.

Just now, nicknorman said:

Blow by is much as you describe - combustion gasses getting past the pistons rings and pressurising the crank case, leading to excessive oil consumption and smoking.

 

But the cause might not be excessive wear, it could also be bore glazing. This is where combustion residue builds up as a kind of gum or varnish on the bores, maybe the piston rings get a bit sticky in the piston ring grooves too, all resulting in poor sealing between the pistons and the bores. This can be caused by low combustion temperature ie running the engine at a very light load (idle) for long periods and or using oil that is too “fancy” for the engine.

 

So it might just be that the bore glazing needs to be removed - this still requires the cylinder block off, but the process is just one of honing (pretty much scraping the gunge off the inside of the cylinders, rather than a rebore. Depending on how bad it is, things might even be improved just by running the engine hard (on a river, not on a canal!) for a while to get the cylinder insides really hot. I think it is called the “Italian tuneup”.

 

But of course with all that said, maybe the engine is indeed badly worn.

Ha cross post he is more technical than me!

[dmr]

It might even be sticky rings and so a "boaters tune up" might fix it (Italians do not have narrowboats).

How many hours has the engine done?.

The fact that the current owners have priced up over sized pistons suggests that they likely know/strongly suspect that the bores have gone.

 

The op needs to make a decision on this boat now and working out what the problem is will likely take some time. The head needs to come off for a definitive answer and if the bores are gone its sad to pay for a gasket set to put the head back on a sick engine.

 

We were in a very similar situation 13 years ago. We negotiated a bit off the price to cover an engine overhaul but on investigation a brand new like for like engine made more sense.

 

If the bores have failed due to wear in the turn-around area then I think (not sure) that things can go downhill quite quickly.

 

My advice would be to negotiate the price down on the assumption that a new engine is needed and if this is not the case then its a bonus.

I don't think rebores and resulting total rebuild are cost effective on an engine like this.

 

Note that the "tune up" can be done roped up in a suitably remote lock ?.

 

................Dave

[Bee]

Can't tell without spending some time looking it over but an engine does need to do a lot of hours to actually wear enough to genuinely need a rebore etc. As others have said spending hours running just to charge batteries is not good practice. Of course it could have been a second hand engine put in a new boat, who knows. Thing is that you have done 100 miles or so with no problems so there might not even be a problem at all. A handy geezer with a compression tester who needs a case of supermarket beer would tell you all you need to know in an hour or two. A quick test is to take the oil filler cap off with the engine ticking over, it will puff some fumes out but if it puffs like an ancient steam engine pulling a couple of hundred tons of coal up a hill then it needs looking at properly.

[Tony Brooks]

I would check the crankcase breather system has not got gunged up before doing much more. I am with Bee, if its starting easily from cold, not consuming much oil and there is not excess exhaust smoke then as you have done several day's boating it could go on for years.

[cuthound]

How many hours has the engine done?

 

Some of the early Ownerships fleet had these engines fitted and they seemed to last 8-10,000 hours before needing replacement, caused by excessive bore wear.