diesel bore wear test?

[homer]

I am wondering whether the following test is of any significance. Having had to remove the head af my VP2002 anyway, I thought I might check the piston/bore seal by pouring a small amount of diesel on top of the pistons and seeing how quickly it drained through to the sump (the oil is due to be changed anyway!). One cylinder dropped about 2 millimetres in 10 minutes, the other showed no noticeable difference. (24 hours later, both had drained completely.) Is this likely to be of any significance?

 

[ccscott49]

Not really a good test, I would expect the diesel to run away, there are gaps in the piston rings, the only real way, now you have the head off, is to measure the bores, with an internal micrometer and an ovality gauge, this will show whether the bores are worn, but not the rings, unless you want to pull the pistons, the only real way is by a compression test, ensuring the valves are in good fettle. You can also check the top of the bores, where the piston rings never get to, and see if theres a discernable "lip" or "Step" worn in the bores, your finger nail will show you this, however, were you burning oil before you pulled the head and was it a bugger to start, no power or any other lack of compression issues?

 

[homer]

Yes, I expected it to run away but thought that the big difference in the rate between the 2 cylinders might be significant. There is a noticeable step using the finger nail test - I guess I will have to get it measured. Recently (and quite suddenly) it has been using oil and starting has been difficult (and it tends to start on one cylinder only).

 

[oldharry]

If there is a noticeable wear step at the top of the bores, then they are worn! Note that the bores will have worn oval because of the way the pistons run, and this is entirely normal. measuring the wear needs a degree of skill to get the exact diameters, but if the step is big enough to click your nail on, then dont waste time - it near enough to needing a rebore to be not worth the time and cost of re-assembly without it!

The oil test you did tells you one thing: oil runs away quicker on one piston than the other! Far more significant is the fact that the engine was difficult to start and then fired on one cylinder while cold. This coupled with the sudden increase in oil consumption suggests you have a broken ring, and they will alomst certainly be certainly badly worn. Rings wear quicker than bores anyway, and you should remove the rings, place one down its bore, and measure the gap between the ends. the makers specify a maximum here, which if exceeded will result in reduced compression , and increased oil consumption. If it is worn, then the rest have to go anyway, so again dont waste time measuring each one!

Better still is to get it to an engine builder who can check the bores and crank at the same time, fit new bearing shells, rebore the block and set up the new pistons so that you know the bottom end is all OK. Costs several hundred - but a LOT less than a new engine! In the meantime you can be checking out the rest of the engine, service up the head, removing the valves and re-seating them, putting new stem seals in etc. If a ring has broken you need to find out why - they dont often break without cause - blocked waterways in the cooling jacket being a possibility for example.

Or you can just junk the lot and install a new engine! A whole lot quicker and saves a lot of mesing about with old ancillary parts that may or may not be on their last legs - alternator, fuel pumps, starter motor, internal oil pump, camshaft etc etc. Remember all these parts will have had the same use as the parts you are replacing and will probably be nearing the end of their service lives too. There has to be a pretty good reason for rebuilding an older engine rather than replacing it - cost being the usual one!

 

[ccscott49]

It's what is technically termed, knackered! I would probaly just go for a new engine, as all the other bits are probably well worn by now!