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lister jp3 rebuild

station tug

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station tug Proficient

station tug

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iv started to strip one of my jp engines today. the big end bearings dont look great to me, they seem dull and have a few grooves in them when you run your finger over them......what are my options as regards replacing them, are they availible as new old stock or is it better to have them re metalled??will i need to take the crank out if im going down the re nmetling route??any idea of cost?

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Timleech Veteran II

Timleech

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Don't worry too much about the odd groove, most well-used bearings will collect those. It's all a matter of degree. Can you post a picture?

More important are bearing clearances, and whether the crankpins are round.

No point putting new bearings on worn crankpins, though you'll get away with a thou or so of ovality on the crankpin if everything else is good.

A JP3 in a narrowboat is never going to be heavily stressed. What are you aiming for, a 'new' engine or one which will do a decent job for a few years?

 

Tim

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station tug Proficient

station tug

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i want to put the engine into a boat and be able to run it...im not really after a new engine just something that will start and run reliably....

 

IMAG0508_zpsd8d78c23.jpg

 

IMAG0504_zps242307c1.jpg

 

IMAG0503_zpscf1a19be.jpg

 

IMAG0501_zpscf003001.jpg

 

these pics are all of the same bearing...iv only got number 3 out so far ill go to the workshop tommorow and remove the other two.......

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martyn 1 Community Regular

martyn 1

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Wear in the big ends only affects starting and reliability when it is so severe as to reduce compression and oil pressure.

 

If they don't rattle when you shake them, I'd say they are fine!

 

 

MtB

Or you could do the job properly once and know its right by measuring the journals and internal diameter of the bearings frusty.gif . If not to badly scored and if within the tolerences refit, and if outside of it replace.

 

Big ends should have 0.003 to 0.004" clearance when new with over 0.006" being a fail and in need of replacement.

 

Mains should have 0.004" to 0.0055" clearance when new with over 0.008" being a fail and in need of replacement.

 

Maximum taper on the journals should be nil to 0.0003" when new with over 0.001" being a fail and in need of regrinding.

 

Crankshaft endfloat should be 0.00275" to 0.0065" clearance when new with over 0.012" being being a fail and in need of replacement.

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Timleech Veteran II

Timleech

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The best way to measure the clearances on worn bearings is to use plastigage. (qg).

 

N

 

I considered suggesting that, but to use it the bearing really needs to be assembled onto the crankpin without rotation, and that might be difficult with a JP.

Might be easier with the rod projecting out through one side door, rather than into the cylinder.

 

Those bearings superficially don't look too bad, no evidence of hammering through excess clearances.

There's a defect near the edge of the top shell, could have been faulty metalling when new or maybe assembled onto some foreign matter, worth checking that the surrounding white metal is secure.

 

Tim

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RLWP Veteran II

RLWP

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Big ends should have 0.003 to 0.004" clearance when new with over 0.006" being a fail and in need of replacement.

 

So, 0.060" on the big end of the Lister-Petter AC1W I recently examined is probably a fail then...

 

Richard

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Timleech Veteran II

Timleech

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So, 0.060" on the big end of the Lister-Petter AC1W I recently examined is probably a fail then...

 

Richard

 

Nah, those things rattle anyway, you probably wouldn't notice the difference....

 

 

Many moons ago, we had a JP2 fail on a camping barge at the start of the season, fractured oil pipe, & the captain kept it going until it stopped. What a mess, all the oil spread around the engine room.

The show had to be kept on the road, I pinched some shells from another engine, luckily a smaller size, and scraped & shimmed them so that they would turn freely on the bu**ered crankpin, which I seem to remember was around 50 thou oval. Kept it going right through the season, by treating it gently and removing shims as the white metal wore, then did a proper job with crank grind and 1/16" undersize shells at the end of the season.

 

Tim

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martyn 1 Community Regular

martyn 1

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So, 0.060" on the big end of the Lister-Petter AC1W I recently examined is probably a fail then...

 

Richard

clapping.gif Well Richard, different engine, different tolerances. but as a guess without looking in the manual for the AC's I would say that is pretty well shot.

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RLWP Veteran II

RLWP

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:clapping: Well Richard, different engine, different tolerances. but as a guess without looking in the manual for the AC's I would say that is pretty well shot.

Indeed. I don't like condemning engines, that one is dead

 

Richard

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MtB Veteran II

MtBDonate to Canal World

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Indeed. I don't like condemning engines, that one is dead

 

Richard

 

Is it really? Back in the day I thought crankshaft regrinds were -0.020", -0.040" and -0.060", with new shells available to match.

 

Or is that rebores and new pistons?

 

 

MtB

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RLWP Veteran II

RLWP

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Is it really? Back in the day I thought crankshaft regrinds were -0.020", -0.040" and -0.060", with new shells available to match.

 

Or is that rebores and new pistons?

 

 

MtB

 

That's 0.060" of excess piston travel. Heaven knows what the crank will be like, plus the cost of bearings, the bore was shot and a piston over £150, plus machining and on and on and on

 

Richard

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