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WANTED JP big end shells


tommylad
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I've just noticed the dreaded white metal in my oil tank filters and on further inspection I've found that the repro big end shells I fitted only 500 hours ago have given up the ghost :( They weren't tight when fitted, lubrication is good and it hasn't been knocking, so my only thought is that it's a quality issue with the shells. Any chance someone has a pair (for one big end) of undersize shells they'd be willing to sell? I need 10 thou undersize or smaller such that I can get them machined out - thank you!!

20220925_085500.jpg

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It won't be cheap but why not get those remetalled? Im sure a internet search or maybe even looking in the vintage engine/car mags might provide  a lead....unless you can find some proper NOS....but the Indian stuff as you have found is crap!

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Yes, I think that could be the best option for a more long term solution. When I rebuilt it I was only able to find one NOS big end bearing, which is still fine - but the repro one is really dissapointing. I guess these parts are principally intended for engines which run at the occaisional steam rally, not clocking up proper hours under load in a boat! Coventry boring remetalled my main bearings and although not cheap I was really pleased with the work they did - I'll give them a call.

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11 hours ago, tommylad said:

Yes, I think that could be the best option for a more long term solution. When I rebuilt it I was only able to find one NOS big end bearing, which is still fine - but the repro one is really dissapointing. I guess these parts are principally intended for engines which run at the occaisional steam rally, not clocking up proper hours under load in a boat! Coventry boring remetalled my main bearings and although not cheap I was really pleased with the work they did - I'll give them a call.

 

If that was some time ago, their whitemetalling man has moved to Coventry Classics.

 

Richard

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Hamlins in Bridgewater did a lovely regrind and re metalling job on two sets of mains and big ends  for me.  Kelvins-  a J3 and a J2.

 Cox and Turner will also remetal a big end and bore to a size without needing the crank.

N

 

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3 hours ago, RLWP said:

 

Did you enjoy Cov Classics?

 

Richard

Yes thanks! Lots of lovely engines lying around! I particularly liked the NEW 6 cyl Riley blocks they're machining up!

I've left the big end with them - Martin was very relaxed about the job, apparently the smaller the bearing the harder it is to remetal, so a JP one should be a doddle!

1 hour ago, BEngo said:

Hamlins in Bridgewater did a lovely regrind and re metalling job on two sets of mains and big ends  for me.  Kelvins-  a J3 and a J2.

 Cox and Turner will also remetal a big end and bore to a size without needing the crank.

N

 

Many thanks BEngo, but as above I've taken it to CCE,

 

Cheers,

 

Tom

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Did you check the crush when you fitted the shells?  There appears to be some minor evidence of white metal fusion, and an odd dirt scratch which may be whitemetal bits going round again,  but the majority of the damage looks like failure of the bond between whitemetal and the shell.   This can be caused by poor tinning of the shells or by shell flexion when there is insufficient crush to keep the shell firmly in contact with the rod and cap.

 

Also worth checking that the bearing seating in the rod and cap is still  properly a cylindrical.  CCE will probably do this automatically.  C&T and Hamlins do.

 

N

 

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14 hours ago, tommylad said:

Yes thanks! Lots of lovely engines lying around! I particularly liked the NEW 6 cyl Riley blocks they're machining up!

I've left the big end with them - Martin was very relaxed about the job, apparently the smaller the bearing the harder it is to remetal, so a JP one should be a doddle!

 

 

They're impressive, those blocks. I didn't get them to unpack the crankshafts they had in a box

 

Richard

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  • 2 weeks later...
On 04/10/2022 at 20:22, BEngo said:

Did you check the crush when you fitted the shells?  There appears to be some minor evidence of white metal fusion, and an odd dirt scratch which may be whitemetal bits going round again,  but the majority of the damage looks like failure of the bond between whitemetal and the shell.   This can be caused by poor tinning of the shells or by shell flexion when there is insufficient crush to keep the shell firmly in contact with the rod and cap.

 

Also worth checking that the bearing seating in the rod and cap is still  properly a cylindrical.  CCE will probably do this automatically.  C&T and Hamlins do.

 

N

 

Many thanks for this BEngo - I did check and had (and still have) the 2 thou nip stated in the manual. Would be good to have cylindricity checked wouldn't it - although I guess it must be very close anyway else the bearing would've been tight when fitted.

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15 hours ago, tommylad said:

Many thanks for this BEngo - I did check and had (and still have) the 2 thou nip stated in the manual. Would be good to have cylindricity checked wouldn't it - although I guess it must be very close anyway else the bearing would've been tight when fitted.

 

 

OFF-TOPIC

 

When working on experimental Stirling engines, we used to get the pistons checked by the metrology department, including cylindricity. They always pointed out, cylindricity is something they couldn't measure. 

 

They can measure straightness, they can measure roundness, they can measure concentricity - but they had no 'cylindricity' measuring tool

 

Richard

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39 minutes ago, RLWP said:

 

 

OFF-TOPIC

 

When working on experimental Stirling engines, we used to get the pistons checked by the metrology department, including cylindricity. They always pointed out, cylindricity is something they couldn't measure. 

 

They can measure straightness, they can measure roundness, they can measure concentricity - but they had no 'cylindricity' measuring tool

 

Richard

 

Also slightly off-topic and following on. While the pistons on a Stirling engine, being an external combustion engine, probably are cylindrical those on a modern petrol or diesel engine should be slightly oval and slightly tapered. This is so they end up cylindrical when hot. Particularly true of aluminium pistons. Posted just in case someone reads this and wonders why their pistons are oval.

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1 hour ago, RLWP said:

 

They can measure straightness, they can measure roundness, they can measure concentricity - but they had no 'cylindricity' measuring tool

 

Still OT,

 

When I was involved with making turbo charger bits we used to measure cylindricity of the shafts frequently.  It was easiest with a co-ordinate measuring machine, but could also be done in a bench centres with a bank of dial  indicators.  Setting the gauge was not easy, I admit, but once it it only needed to be checked against a reference piece.

 

  A standard three point bore gauge will also measure bore cylindricity.

 

 

The other reason  for ICE pistons being oval by design is to accept the side thrust when the engine fires. The long side is at right angles to the gudgeon pin, so the piston is forced into a round shape as the pressure rises.

 

N

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2 hours ago, RLWP said:

 

 

OFF-TOPIC

 

When working on experimental Stirling engines, we used to get the pistons checked by the metrology department, including cylindricity. They always pointed out, cylindricity is something they couldn't measure. 

 

They can measure straightness, they can measure roundness, they can measure concentricity - but they had no 'cylindricity' measuring tool

 

Richard

 

A photo of one of the Stirling engines that I installed as part of a failed project for the supermarket chain  Waitrose, partially dismantled.

 

IMG00164-20130108-1354.jpg

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On 15/10/2022 at 10:01, BEngo said:

A standard three point bore gauge will also measure bore cylindricity.

 

Technically, it doesn't. It measures straightness, roundness and concentricity. You can infer cylindricity from those figures, not measure it

 

Richard

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1 hour ago, RLWP said:

 

Technically, it doesn't. It measures straightness, roundness and concentricity. You can infer cylindricity from those figures, not measure it

 

Richard

Would it detect that the hole was leaning?  A bit like a stack of coins each staggered a little in the same direction?  Put another way, a cylinder with a little wedged shape bit top and bottom. 

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Hand held, probably not. I think you would need to constrain it to vertical movement to hope to àdetect a leaning hole. Even then the results might be difficult to interpret.

 

That said a leaning hole could still be acceptable in cylindricity, but it might fail on squareness, or parallelism, or both.

 

N

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On 15/10/2022 at 08:34, RLWP said:

 

 

OFF-TOPIC

 

When working on experimental Stirling engines, we used to get the pistons checked by the metrology department, including cylindricity. They always pointed out, cylindricity is something they couldn't measure. 

 

They can measure straightness, they can measure roundness, they can measure concentricity - but they had no 'cylindricity' measuring tool

 

Richard

No, I guess you really need a CMM for properly checking it

On 15/10/2022 at 09:18, Tony Brooks said:

 

Also slightly off-topic and following on. While the pistons on a Stirling engine, being an external combustion engine, probably are cylindrical those on a modern petrol or diesel engine should be slightly oval and slightly tapered. This is so they end up cylindrical when hot. Particularly true of aluminium pistons. Posted just in case someone reads this and wonders why their pistons are oval.

Yes, I'm baffled as to how they machined pistons before CNC machines?

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2 minutes ago, tommylad said:

No, I guess you really need a CMM for properly checking it

Yes, I'm baffled as to how they machined pistons before CNC machines?

 

When I did my time pistons were referred to as taper turned and oval ground. I can see taper turning should be easy enough and I suspect a grinding wheel brought in and out by a cam on the lathe would do the oval grinding.

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2 minutes ago, Tony Brooks said:

 

When I did my time pistons were referred to as taper turned and oval ground. I can see taper turning should be easy enough and I suspect a grinding wheel brought in and out by a cam on the lathe would do the oval grinding.

Ah I see - sounds obvious when you explain it! Interesting how one CNC machine can do the work of so many customized ones

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1 minute ago, tommylad said:

Ah I see - sounds obvious when you explain it! Interesting how one CNC machine can do the work of so many customized ones

 

Actually I am far from sure that pistons are not die-cast these days so need little machining. Just reaming for the gudgeon pin and turning for the ring grooves. Anyway, I have no direct knowledge of how they are made.

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3 minutes ago, Tony Brooks said:

 

Actually I am far from sure that pistons are not die-cast these days so need little machining. Just reaming for the gudgeon pin and turning for the ring grooves. Anyway, I have no direct knowledge of how they are made.

Impressive that the as-cast surface is that good, both wrt surface finish and geometrical accuracy

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Depends on your piston.  Many, particularly high-performance ones,  are forged then CNC turned.  Others are pressure die-cast  but since the ring grooves still  have to be turned, the oil drain holes drilled and the  circlip grooves and the gudgeon pin bearings machined I think that die cast pistons are still CNC machined to put the taper etc. on.  Modern casting dies can be very accurate, but they do wear and distort with use.  Molten Al alloy is  pretty hot and the automatic casting cycle is not gentle on the dies so there is usually some flash somewhere where you do not want it.

 

That said, I have never been involved in piston making.  Turbo charger compressor wheels, which I have been involved with, are also pressure die cast, and they too have to be turned to get the outside shape and size right, though the blade faces are not machined.

 

  Incidentally, piston turning is one of those jobs where a real diamond is the tool of choice for turning, but diamonds won't take big cuts, hence near net shape dies are needed to save machining time.

 

N

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