Bent Conrod!

[sociable_hermit]

Yep, I get that. It was the bend in the piston rod on 73096 that concerned me. At the moment the water causes the piston head to stop, the top end of the con rod will have nowhere to go, while the bottom end is still moving. This will bend the rod but wouldn't it also try to push the small end sideways? If the con rod is no longer absolutely central to the piston head then Gibbo's logic no longer applies because there will be forces in other directions too! But yes, I see what he is saying and strictly speaking this wouldn't be the result of the con rod itself being bent. Must get me terminology right!

[Proper Job]

You say the pistons are different. Have you checked that the height from gudgeon pin pore to piston crown is the same on all three? A discrepancy could be a contributing factor to the reduced compression.

 

Tim

I like your thinking Tim. Difference in the swept volume to the clear volume will give a totally different compression ratio on that cylinder. That, compounded with the bent conrod could/would have a major impact on slow running/light load performance.

 

By the way guy's - don't start personal insults. The mods will close the thread down and this has the makings of a good proper engineering thread. I sure its just a case of quick posting and miss construed comments

 

edited to add:

Take in to account my last sentence: Whilst I note that the forces are going in the same direction, irrespective of how bent out of true the conrod is; I would be seriously impressed by a three foot distortion of a 3VRO conrod

Edited April 2, 2009 by Proper Job

[Proper Job]

It isn't entirely irrelevant - although the connecting rod of an internal combustion engine may have a small-end gudgeon pin in place of an external crosshead and guide it is still important for the force to be transmitted evenly. A connecting rod or piston rod (internal combustion or steam) is carefully designed to withstand and transmit the force of ignition/expansion to the crankshaft and the relative positions of the gudgeon pin and big end bearing are taken into consideration during the design process. If this was one of my connecting rods I would want to get it back to the exact dimensions, specifications and tolerances that the designer intended.

 

The damage illustrated with a steam locomotive piston on the Mid Hants Railway is an indication of what can happen (on any engine) if water gets into a cylinder and cannot escape.

Not entirely true Graham. Large marine diesels are of a similar configuration to your beloved steam locomotives. The piston is connected to a piston rod, and the top of the connecting rod is run in a crosshead bearing.

 

Link

 

I have to say this one a bit bigger that the ones I've worked on (max 36,000hp)

 

Ain't she a beauty

[Gibbo]

........so I'd appreciate it if you didn't speak to me like a complete idiot, Gibbo!

 

I did no such thing. I was confused by the lack of relevance between a steam engine that has a fixed rod coming out of a cylinder end (which can bend and affect the direction of forces) and an IC engine con rod which can bend and make no difference to the direction of forces.

 

If you think that's treating someone like a complete idiot wait till someone says something really stupid

 

Gibbo

[sociable_hermit]

Sorry, was being a bit hyper-sensitive there!

[MoominPapa]

The way I see it, the crucial measurement for compression ratio is from the centre of the big-end journal to the deck of the piston. If that is reduced, then the compression ratio will be reduced because the cylinder volume at TDC is increased but the swept volume stays the same. That could occur either because the con-rod bent in-plane or the piston was squashed and distorted by the hydraulic lock or the wrong piston was fitted on repair.

 

If the con-rod bent so that the big-end and little end bushes are no longer parallel, then lots of nasty forces would be generated. I suppose that possible, the rod won't be completely symetrical or homogenous, so to could squash more on one side that the other.

 

MP.

[billh]

The ruston VRO engines are bomb proof- they had to be , they were used for generators on WW2 searchlights. You could probably straighten the con-rod with a lump hammer . I have been using a similar 3VRH on and off for 30 years in a crane, sometimes it lies unused for 12months but it always starts on the enormous handle , with the help of easystart or by lighting a fire in the wick thing in the inlet manifold. Once started she runs on 2 cylinders until you get some load on then all 3 .The compressions are all over the place , maybe the rods are bent , who knows? She 's always been like that. I understand why you might not be able to live with it in a boat in that state, so I hope your engineering solution proves to be ok. If not , you could try the nice people at the Internal Fire Museum ( diesel engine museum in South Wales) . They may be able to find you a rod or a even a complete engine in exchange for a suitable donation to funds.

As an aside , the last time we needed the Ruston, 3 mice ( possibly blind ones ) ran out of the radiator filler , as we put water in- not sure if they were living in the rad. or the engine.

Bill

[NB Alnwick]

Not entirely true Graham. Large marine diesels are of a similar configuration to your beloved steam locomotives. The piston is connected to a piston rod, and the top of the connecting rod is run in a crosshead bearing.

 

Link

 

I have to say this one a bit bigger that the ones I've worked on (max 36,000hp)

 

Ain't she a beauty

 

We built some big engines at English Electric when I was there in the 1960s but nothing anywhere near that scale.

[Arnot]

I did no such thing. I was confused by the lack of relevance between a steam engine that has a fixed rod coming out of a cylinder end (which can bend and affect the direction of forces) and an IC engine con rod which can bend and make no difference to the direction of forces.

 

If you think that's treating someone like a complete idiot wait till someone says something really stupid

 

Gibbo

 

something really stupid

 

 

Arnot

[Arnot]

The ruston VRO engines are bomb proof- they had to be , they were used for generators on WW2 searchlights. You could probably straighten the con-rod with a lump hammer . I have been using a similar 3VRH on and off for 30 years in a crane, sometimes it lies unused for 12months but it always starts on the enormous handle , with the help of easystart or by lighting a fire in the wick thing in the inlet manifold. Once started she runs on 2 cylinders until you get some load on then all 3 .The compressions are all over the place , maybe the rods are bent , who knows? She 's always been like that. I understand why you might not be able to live with it in a boat in that state, so I hope your engineering solution proves to be ok. If not , you could try the nice people at the Internal Fire Museum ( diesel engine museum in South Wales) . They may be able to find you a rod or a even a complete engine in exchange for a suitable donation to funds.

As an aside , the last time we needed the Ruston, 3 mice ( possibly blind ones ) ran out of the radiator filler , as we put water in- not sure if they were living in the rad. or the engine.

Bill

Sounds like a similar problem...

 

My engine would run on all three under load and on accelleration it just wouldn't fire number three on tickover when warm or hardly ever when cold. It wouldn't be a problem as far as propelling the boat goes, but the clouds of white unburned diesel obliterated a 100 yard downwind swathe and it would have made steering pretty arbitrary if the wind was in the wrong direction.

 

I have to say that when you consider the size of the conrod it beggars the imagination to work out how much force it took to bend it, it would need some class of lump hammer to make it good. The VRO is certainly built to be bombproof, I don't think I have ever seen such a solid or well engineered engine of this capacity. I will try to post some piccies eventually.

 

Anyway, my visit to the engineers was productive. It seems that the ends of the conrod are still in line and the bending is only across the axis of the engine. After some discussion it was agreed that apart from another hydraulic lock, it would be unlikely to give problems in service and since there was a risk of breakage or further damage to the rod by trying to straighten it we were best leaving well alone. If it broke, the engine would probably be beyond economical repair.

 

So... we are going the route of fitting a new bush and boring it off centre to raise the piston crown height. We did check the pistons and although number three is clearly a different make, the gudgeon pin to crown dimension is identical, only the two slight depressions in the rim to give valve clearance are slightly different and this will only amount to a difference of about 1% of the compressed volume, probably one of the lesser variables given the age and conditon of the engine so we are not going to worry about this one.

 

The engineers (who do seem to know their stuff and are really very helpful) tell me that due to the credit crunch, lots more people are having engines rebuilt rather than changing them so they are unusually busy, as a consequence it will be a couple of weeks before my rod is ready. I just hope I can still remember how to reassemble the engine by then (or who I am for that matter or what the boxes of bits were in the first place).

 

Better examination of the bores indicates that there is no eccentric wear evident which bears out the results of the conrod examination. Interestingly number one bore and piston show signs of having "picked up" at the bottom of the skirt at some time in the past but the damage is fairly minor and well clear of the area swept by the rings.

 

I do have a slight concern here though, if number three piston is raised by 50 thou to bring it in line with the other two and balance the compressions, the slight lip at the top of the bore where the rings stopped previously might do some damage to the top compression ring. I am wondering if it would be a good idea to hone the top land of the bore to elimiate the step - ideas?

 

Regards

 

Arnot

[Timleech]

I do have a slight concern here though, if number three piston is raised by 50 thou to bring it in line with the other two and balance the compressions, the slight lip at the top of the bore where the rings stopped previously might do some damage to the top compression ring. I am wondering if it would be a good idea to hone the top land of the bore to elimiate the step - ideas?

 

Regards

 

Arnot

 

There used to be things called 'ridge reamers' available to do exactly that job. Maybe you could find one somewhere in the size you need if you looked long and hard enough. Stepped piston rings were another traditional answer, where the top ring has a reduced diameter at the top, but finding those for your engine 'off the shelf' seems pretty unlikely.

 

Otherwise you have two options, as I see it -

1. take the block to your friendly engineering shop & have them do it

2. If you reckon you're good with a die grinder, do it yourself very carefully freehand, finish with a flap wheel or similar.

Much depends on how much wear there is.

 

Tim

[Arnot]

There used to be things called 'ridge reamers' available to do exactly that job. Maybe you could find one somewhere in the size you need if you looked long and hard enough. Stepped piston rings were another traditional answer, where the top ring has a reduced diameter at the top, but finding those for your engine 'off the shelf' seems pretty unlikely.

 

Otherwise you have two options, as I see it -

1. take the block to your friendly engineering shop & have them do it

2. If you reckon you're good with a die grinder, do it yourself very carefully freehand, finish with a flap wheel or similar.

Much depends on how much wear there is.

 

Tim

At great expense, I now have my conrod back from the machinists with an offset small end bush, it was decided that it was too risky to try straightening it. Of course, sod's law kicked in over the weekend and a contact came up with a brand new conrod at less than half the price! Such is life...

 

I will have a go at rebuilding the engine over the next few days and report back. I intend to relieve the ridge in the cylinder with a honing tool which should bring about the desired result, stripping the block and taking it to the machine shop would take for ever and cost a fortune..

 

Regards

 

Arnot

[Gibbo]

I intend to relieve the ridge in the cylinder with a honing tool.................

 

 

 

Gibbo

[Yoda]

Half round bastard!

[paulcatchpole]

Half round bastard!

 

That's really, really amused me.

 

I'm sad.

 

PC

[Arnot]

Half round bastard!

Actually I'm very round!

 

Progress update...

 

The repaired conrod is now firmly bolted in place (along with the other two as well) and all looks good. The piston crowns are now within a thou or two of each other and the bump clearances are within spec. Everything that should move does and everything that shouldn't doesn't.

 

Hopefully tomorrow, after a couple of boat repairs, I should have time to finish off assembling all the fiddly bits and bobs and see if the old gal fires up sweetly.

 

If I can work out how to include and image in a posting, I will show some picces of the conrod repair.

 

Regards

 

Arnot

[ditchcrawler]

Actually I'm very round!

 

Progress update...

 

The repaired conrod is now firmly bolted in place (along with the other two as well) and all looks good. The piston crowns are now within a thou or two of each other and the bump clearances are within spec. Everything that should move does and everything that shouldn't doesn't.

 

Hopefully tomorrow, after a couple of boat repairs, I should have time to finish off assembling all the fiddly bits and bobs and see if the old gal fires up sweetly.

 

If I can work out how to include and image in a posting, I will show some picces of the conrod repair.

 

Regards

 

Arnot

Good luck for the test run

[Arnot]

Good luck for the test run

 

Ta!

 

Well.... IT WORKED!

 

I fired it up about an hour ago and once the injectors had all purged the air in them it now ticks over nice and smoothly and responds to the go faster lever quickly and all without clouds of white smoke and flames.

 

There are still a few minor niggles such as leaking filter housings, a mysterious knock from something connected to the camshaft (half engine speed) and a leaking water pump. Once these are sorted out, I can get it painted and set about making the mountings, completing the hydraulic drive system and shoehorning it into my boat. I will be soooooooo glad to get rid of the Petter PJ4 I have at the moment, it rattles like a bunch of skeletons having an orgy on a tin roof.

 

Regards

 

Arnot

[Bob the welder]

Ta!

 

Well.... IT WORKED!

 

I fired it up about an hour ago and once the injectors had all purged the air in them it now ticks over nice and smoothly and responds to the go faster lever quickly and all without clouds of white smoke and flames.

 

There are still a few minor niggles such as leaking filter housings, a mysterious knock from something connected to the camshaft (half engine speed) and a leaking water pump. Once these are sorted out, I can get it painted and set about making the mountings, completing the hydraulic drive system and shoehorning it into my boat. I will be soooooooo glad to get rid of the Petter PJ4 I have at the moment, it rattles like a bunch of skeletons having an orgy on a tin roof.

 

Regards

 

Arnot

well done

[Gibbo]

There are still a few minor niggles such as leaking filter housings, a mysterious knock from something connected to the camshaft (half engine speed)

 

I've got one of those on my Gardner. I was told it sounded like the injector pump. My reaction was "ahh, be reet" and I left it. A few thousand hours later and it still works fine.

 

Gibbo

[Proper Job]

If it was a JP Lister, it's definitely the fuel pump coupling I spent many wasted hours trying to shim it to silence. Gave up

 

They all make that noise

[Timleech]

If it was a JP Lister, it's definitely the fuel pump coupling I spent many wasted hours trying to shim it to silence. Gave up

 

They all make that noise

 

They don't if you fit a new one, made to fit.

For at least a couple of weeks

 

Tim

[Arnot]

If it was a JP Lister, it's definitely the fuel pump coupling I spent many wasted hours trying to shim it to silence. Gave up

 

They all make that noise

As it happens the Ruston 3VRO is a close cousin of the JP3 and there are quite a few parts in common, one being the fuel pump and it's drive system...

 

I have spent all afternoon trying to identify the cause of the knocking. Once I know what it is I may well decide to live with it but I do want to know that it isn't the portent of nastier things.

 

The problem I have is that the noise is related to the camshaft movement and is more pronounced at lower speeds and the injector pump drive clacking away and the injectors popping do tend to obscure the sound a bit.

 

This afternoon, I have disconnected the fuel pump and taken the cover off the camshaft drive gears to see if I can get the noise to occur whilst turning the engine by hand - but I can't. I suspect that the noise is at it's worst at about 100 to 200RPM and I just can't crank it that fast by hand. So... tomorrow (or sometime over the next few days) I am going to rig up a motor to drive the flywheel via a rubber belt to spin the crankshaft/camshaft at a respectable speed and see if this allows me to discover the cause.

 

At the moment I suspect that it might be a combination of the valve springs forcing the camshaft to speed up until the next cam lobe starts to require power to lift the next valve spring. There is a bit of backlash on the camshaft gears that are straight cut and it may just be them banging about a bit. It didn't seem to make the noise when the engine was turned quite fast without the conrods in and without the heads or fuel pump on. We will see...

 

Perhaps I just shouldn't be so fussy!

 

Regards

 

Arnot

 

 

They don't if you fit a new one, made to fit.

For at least a couple of weeks

 

Tim

 

Been there, got the t-shirt

 

Regards

 

Arnot

[Hairy-Neil]

As it happens the Ruston 3VRO is a close cousin of the JP3 and there are quite a few parts in common, one being the fuel pump and it's drive system...

 

The JP in the Lister name stands for Joint Project. Ruston were the other party involved I believe.

[Arnot]

The JP in the Lister name stands for Joint Project. Ruston were the other party involved I believe.

If it hadn't been another era, I would be tempted to think that it was more "joint" than "project"

 

Regards

 

Arnot

Edited May 5, 2009 by Arnot