Author Topic: JP Pistons for Mk4  (Read 2717 times)

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Offline dragonmk5

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JP Pistons for Mk4
« on: 10 Feb 2012 at 10:02 »
Am currently sitting on a pair of standard JP's purchased from the club spares dept and waiting with baited breath, for news of the new barrels which are out for machining.  Regarding the JP's, I have read a few adverse comments about them, the most serious of which relates to poor machining by the manufacturer, consequently I would be pleased ( and grateful ) to receive any tips/advice as to what to look for on the piston so that I can take any remedial action before fitting.

Offline eddie

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Re: JP Pistons for Mk4
« Reply #1 on: 10 Feb 2012 at 11:08 »
Hi,
     From our experience, when involved with LDMCC post war spares, there were a few instances where members reported smokey engines, but these were mostly attributed to incorrect clearances on the bore. Providing you have the bores machined to the correct clearance as stated on the leaflet that came with the pistons, you shouldn't experience any problems. Mr Douglas always made his bores to size (60.8mm = 2.394") with the clearance allowed for on the piston. Some reborers have been known to allow the clearance on the bores (which results in excessive oil consumption).
    The reports you have heard of poor machining probably date back quite a few years when JP suffered a change of management and quality seemed to suffer somewhat. From our experience, the problems seemed to be with the rings rather than the pistons themselves.
     Regards,
              Eddie.

Offline dragonmk5

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Re: JP Pistons for Mk4
« Reply #2 on: 10 Feb 2012 at 15:43 »
Thanks for the super-fast response Eddie.  Regarding the rings, is the problem relative to the grooves or the rings themselves?

Offline eddie

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Re: JP Pistons for Mk4
« Reply #3 on: 10 Feb 2012 at 16:53 »
It was the rings themselves - the width was not constant - usually tapering off at the ends. As I said previously - this was several years ago - and only affected one batch. Later batches were back to the expected standard.

      Eddie.

Offline dragonmk5

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Re: JP Pistons for Mk4
« Reply #4 on: 11 Feb 2012 at 08:24 »
That's good to know - I can go back to sleep now!
Thanks and regards

George