Author Topic: Mk piston  (Read 466 times)

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Offline Andy Smith

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Mk piston
« on: 20 Jul 2017 at 23:35 »
Hi all I have stripped the mk V looking at the pistons the two bottom rings are very tight in the groove so much that they appear to be pointless I think they are replacements for a oil ring (I think pre-war Velo Mss had something similar) is it wise to see if I can successfully widen the gap to see if they will "spring"out and improve compression or oil scraping (AE +60) I don't know if it burned much oil I it appears that it has not been OTR for many years judging by the condition inside Best wishes Andy

Offline Hampshirebiker

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Re: Mk piston
« Reply #1 on: 21 Jul 2017 at 05:48 »
If you can remove the rings, it's better to just clean up the groove. They've probably just got stuck over the years. Make sure you've got the correct ring gap, before reassembly.
More informed opinion may follow.

Offline eddie

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Re: Mk piston
« Reply #2 on: 21 Jul 2017 at 07:10 »
Hi Andy,
             A stepped scraper is the correct ring for the bottom groove on Mark 5 pistons. After giving the ring a dose of WD40, warm the piston with a hot air gun. If the ring is still stuck, start from the gap and try tapping it with a piece of hard wood until it frees up. Eventually, the ring should spin freely in the groove.
  Regards,
               Eddie.

Offline douglas1947

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Re: Mk piston
« Reply #3 on: 21 Jul 2017 at 13:06 »
Hi Andy,

what Eddie have written, thatīs the way you should try.
Be very carefull. I had the same problem with pistons and soak them in diesel for several days, free only a bit and soak again, until the ring is completely free.
If your piston is a +.060":
I have a MK4 engine in work, fitted with +.060, but 1 oilsraper is only a Standard (60,8mm). I have tried to get a +.060" ring to fit,but no success.
So be carefull with your ring!

Michael

Offline cardan

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Re: Mk piston
« Reply #4 on: 21 Jul 2017 at 23:36 »

Surprisingly, rings can be (easily?) machined in the lathe. With a sharp high speed steel tool it would be possible to modify a full ring to make a stepped scraper, although I'm not sure exactly what the idea is behind such a thing!

These days I find that modern rings have a lot of tension against the cylinder wall - too much for my old 1920s-and-earlier bikes, so I often remove some depth from the ring in the lathe (by machining the inside) before I fit it, particularly if I'm putting two rings in a single wide groove.

Leon

Offline Andy Smith

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Re: Mk piston
« Reply #5 on: 22 Jul 2017 at 08:03 »
Following Eddies advise and carefull use of a old junior hacksaw blade out they came :D Cleaned up refitted (with ring compressor there's not much lead on these barrels!) "Stepped rings whatever will they think of next" Seriously thanks very much for the steer Andy

 

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