Topic: New build - cylinder scoring concern

[gp_st3]

Is the shiny spot really a problem? It look like a reflection of the valve pocket.

My old 836 cylinder has shiny spots at front. Probably due to way too much total clearance, 0.2mm.  No oil smoking nor drinking..
(Cyl bore diam - piston diam at skirts (front rear).

That's an interesting picture of your worn 836 bore as it shows similar vertical scoring in the same skirt area as I mine (agree that the shiny area on mine is just pocket reflection due to the bright lighting) - I cannot photograph the front face but am assuming it's the same as the rear.

The machinist had not seen CI 836 pistons before and was initially puzzled that they did not have offset valve pockets as he normally works with Wiseco pistons; we agreed on 0.025mm but it seems that should have been nearer to 0.04mm judging my  experience and the comments on this thread.

[PeWe]

Interesting thread here about bore-piston clearance. CI 836 mentioned
http://forums.sohc4.net/index.php/topic,148467.0.html

Lets see if my coated grey CycleX 65.5mm pistons will get tighter than 0.0015" (0.038 mm). I like to run hard from start for best ring seal

[trigger]

0.02mm to 0.025mm is a little too tight for CI pistons, OK for OEM ones, 1 thou to 1.2 thou is a good clearance on these pistons. Your guy that did the rebore seems to know what he was doing but, did he match each piston to its own bore?
 I have used CI pistons for many years but, have found that they can be out by half a thou and sometimes more.

yes, the pistons were matched - I numbered them before handing them over and similar to your experience, on collection about 3 months ago the machinist mentioned that three of the pistons were very close to spec but one was 'a bit out' (don't recall if he said by how much).. remember trying to measure the them with a micrometer but struggled to get a consistent reading due to my lack of experience/skill and just made sure to fit each in the correct bore!

If it is not burning oil i would put a thimble full of oil down each bore and take it for a good run to get it hot and bed in. You have nothing to lose