FOR THE EXPERTS !

And the job was presented to you as a "Can you just look at this"?

Never really did get my head round the PT system, and it got worse as it became more complicated to meet /beat emissions legislation.

Everything would be SO much easier if the engine was out and you had room to work on it, and not have to fish in the bilges for a dropped nut!

You really do need Good Luck!

Howard

The story so far ! valves OK ! head pressure tested ok ! Head gasket seems OK, no obvious sign of blowing and blow down showed no signs. The engine is to be removed, sump taken off, head refitted and whole engine pressure tested ! Liner seals or cracked/pin holed liner, along with bad or broken rings seems the next thing. Pressure testing the block/head will show up any other cylinders on the point of failing ! Oh what fun. Noel.

At one time Cummins and Rolls Royce were troubled by waterside attack so that liners pin holed. R _ R went some way towards a solution by offsetting the gudgeon pin slightly. to reduce piston slap.

I think that Cummins chrome plated the outside of the liner, and used a special additive for the coolant.

Never heard of any problems with the Perkins 4.99 or 4.107, strangely., although superseded by the 4.108, which was a dry liner version of the 4.107, using a slightly different con rod length.

Wet liner engines were always difficult to keep coolant where it should be. The Bristol BV had two tell tale holes, in the block, between the lower liner seals, to indicate whether it was coolant or oil that had passed the seal.

Howard;

Did you check / compare the heights of each piston at TDC?

If top end is OK then as you say a cracked/holed liner seems possible although I'd also be expecting some water in the sump should this be case - one clue to this is if the dipstick oil level rises of its own accord after engine has been sitting. Could be luck depending on whether the piston stops with the leak above or below rings.

Gentlemen, first thank you to all who have commented ! The engine filled a cylinder or more with water over 2 days and hydrauliced, there was also 1/2 a gallon of water in the sump. The head was sound (pressure tested ) the head gasket did not appear to have blown, leaving only a fault connected with the liners. The facilities were a muddy yard, rough grass/ ground, a garage with no lights and the engine weighs about a ton ! I considered this situation to be inconsistant with the standards I would aspire to achieve, so the engine has been taken out and sent to a cummins specialist for overhaul ! This action will save me being blamed for the over run of the deadline !!!!!!! I will in due course report the findings. Many thanks again. Noel.

Gentlemen, further to the above, the engine went away ! One liner was pinholed ! The rest were not good ! The engine had it seems ingested sand which had caused damage to the top ring and groove. All in all a sorry state - and now at 50 years old there are problems getting parts ! Ah well. Noel.

Well that would explain it. The googling I did when you did posted this implied that a poorly 903 was best swapped out for something more modern. It's a bigger beast than I've ever tackled so no idea if there is enough space or how much of a job this is but if the owners want it to run reliably for the future then may be worth considering. Fuel consumption and emissions will likely improve as well.

Now I remember why I refused long ago to work on anything with four wheels, tracks or a rudder. Motorcycles and diesel generators are fine. Stand or sit right next to them and work on them in comfort. Nothing like lying in the mud under a dozer or truck with oil dripping all over you while trying to drop a transmission out with your bare teeth and fingernails. Nice flick pass to the Cummins dealers there. Way to go!

If it did hydraulic it would be a good idea to check the lengths of the relevant head studs/bolts, and the condition of the threads in the various bits affected. And even if the relevant rod 'looks ok' check its length.

The idea of offsetting gudgeon-pins (wrist-pins) is quite common, as is the idea of offsetting the cylinder bore to the centre line of the crank. This latter is called a desaxé design, and the word has three syllables, not two.

Those of a mathematical bent might care to think how such a design affects the calculation of capacity. And how the valve timing can be set when the two dead-centres are not 180 degrees apart ...

Cheers, Tim

Well I am certainly not of a mathematical bent but I am thinking TDC would be when the crank mainshaft, crankpin and gudgeon pin were in a straight line. Which of course would be slightly off from the traditional TDC by a degree or two maybe. You'd have to calculate it, maybe, as the triangle between the crank mainshaft and traditional TDC position and the new gudgeon position when the main, crankpin and gudgeon are aligned. But it make my head hurt to think about it. And practically, there is so very little piston travel that few degrees either side of TDC, I wonder if they even bother to adjust cam timing at all? I suppose they do but it probably doesnt make much difference.

The offset bore could be more so as they use quite a bit offset. Yamaha started using that on their race engines some years back I recollect dimly and now on their street sportbike engines. That kind of mega high performance engine, they would certainly adjust cam and ignition timing to match. Same principle though, I imagine, TDC would be with the main, crankpin and gudgeon in a straight line. .

Hello Hopper

Yes, when they are in a straight line makes sense, in theory. But how do you tell, from the engine in front of you, when they are indeed in line? You can certainly measure the piston position, but where is the crankpin when the piston is furthest up? Or, when the most significant bits of timing (ignition or valves) are around TDC rather than BDC, is that the most relevant place to measure from?

Of course, if you knew what the factory did, easy-peasy, but when the engine was made in a factory bombed in WW2, what chance?

cheers, Tim

Edited By Tim Stevens on 15/03/2022 10:54:19

For timing purposes, I guess it does not matter where the crankpin is. It is piston position that is all important. You would still find TDC and then set ignition timing either number of degrees or distance of piston travel BTDC.

To calculate exact crankpin position you would need to know, I think, the full geometry of the amount of gudgeon offset and the exact crankpin throw and the exact con rod length. Then work out the triangle geometry, or these days draw it up in CAD.

Makes my head hurt just thinking about it. Or as Curly of the 3 Stooges said, I tried thinkin' about it but nothin' happened.