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Piston and ring size markings

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Laverda Dave:
Hi Everyone,
The rebuild of the 400/4 I bought in boxes is progressing well with the engine cases now back from aqua blasting and various essential parts purchased from Mr Silver's parts emporium.  I have also collected the head from J D Autoworx following a 7 thou skim, valve seat cuts for the four new inlet valves and two brass inserts being installed following the removal of the broken exhaust studs on No.3 cylinder.
I dropped the frame off today to have it checked, its just a shame the previous owner had it blasted and powder coated without checking the alignment first.  I am hoping a hot torch isn't going to be required to straighten it if it is bent otherwise it will get a bit messy! A lesson here is that any frame should be checked before stripping and painting especially considering the age of bikes we ride and the probability of the bike having at least one excursion down the road! A Morini I restored a couple of years ago had a perfect looking frame and I was going ahead to paint it but though a check would be a good idea. I'm glad I did, it was 2 degrees out at the steering head!
Anyway, the reason I'm here.........I have been checking the pistons and rings today, plan is to fit a new set of rings only as the previous owner measured the bores and found very little wear and virtually no oval wear at all.  My question is, how do I know what size pistons and rings I have without having access to specialist measuring equipment? I thought the pistons or the rings would be stamped with either 'STD' markings or 0.25 etc for any oversize.  I cannot find either on the pistons or the rings?
Any advice would be appreciated.
I will post a few pics on the site of the rebuild as it progresses when I a chance and have clean hands!
Dave

Bryanj:
Unmarked pistons are normally, but not always, standard. The rings are marked on the top face by the join again no markings are standard BUT I have seen rings worn so much that the markings have disapeared

paulbaker1954:
Have you measured the bores? This is best way to check but FYI I just rebuilt my 4 engine and the Pistons had no markings except the forward arrow and these were standard size

By the way I have a set of std rings if you need and want to make me a sensible offer

They are NOS rings by the way

Laverda Dave:
Thank you both for the advise.

Very helpful, I thought they might be standard as my old 400/4 had 0.25 stamped on the rings when I had that re-bored.

The guy who began the project measured the bores (he's an engineer and has top spec measuring equipment).  He told me the bores and pistons are well within tolerance and sent me a copy of the measurements (attached). I am not an engineer on that level and to be honest I had some difficulty reading the attachment. From what I can see all appears well, the pistons show no sign of blow by although they do have evidence of some scuffing but nothing to be worried about (maybe a photo would help?).
I was just going to put a new set of rings in but............ If anyone reading this thinks the measurements given indicate a re-bore is needed I will take this route. I would like to say the bike has done 47000 miles but......it had a CB250 speedo fitted so any true mileage is guesswork and the engine was in bits and stored in several carboard boxes (I love a challenge........!)
Paul, If all is well and the general opinion is to stay with what I have I will buy those rings from you.  Let me know how much and your details, mail me at davejotaellis@talktalk.net with your price and we can go from there.
Regards
Dave

Bryanj:
If standard bore is 51mm (sorry havn't got that book to hand) you are good to go with new rings and a glaze bust on the bores

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