Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: eight0 on November 04, 2020, 03:06:44 PM
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I just went to pick up the Cylinder Block from the machine shop having instructed them to bore to 1x oversize to .25mm.
I bought a piston which arrived from DSS yesterday and asked if he could just double check the measurements. He said the piston was actually '1thou' bigger than it should be.
He suggested I send the rest of the pistons over so he could bore to the correct size for each cylinder.
Are these pistons known to be a bit rubbish? They did have Chinese lettering on the box. Not sure what do do, do I sent the DSS ones back and buy a different set or just send all the pistons to the machine shop?
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Trigger is your man for the best way forward.
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I always had rebores done to suit already purchased piston sets, with each bore machined to match a chosen/numbered piston, even a matched new piston set each piston can vary in size to each other, micrometer wise
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Cruzinimage on ebay (they are Japan based) have a good reputation - I have used 2 sets with no problem - Trig will be along shortly I imagine with appropriate recommendation!
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I always had rebores done to suit already purchased piston sets, with each bore machined to match a chosen/numbered piston, even a matched new piston set each piston can vary in size to each other, micrometer wise
Exactly. That's the only way to do it.
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I always had rebores done to suit already purchased piston sets, with each bore machined to match a chosen/numbered piston, even a matched new piston set each piston can vary in size to each other, micrometer wise
Yeah the guy at the machine shop said he was happy to go back and do this if I sent him the rest of the pistons. As long as all the pistons are larger than they should be and not smaller!
Learnt a lesson here for next time I guess.
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I always had rebores done to suit already purchased piston sets, with each bore machined to match a chosen/numbered piston, even a matched new piston set each piston can vary in size to each other, micrometer wise
Yeah the guy at the machine shop said he was happy to go back and do this if I sent him the rest of the pistons. As long as all the pistons are larger than they should be and not smaller!
Learnt a lesson here for next time I guess.
Fingers crossed 😉
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There's a need to be careful here particularly around the tolerances they bore too.
Many places just will not accept the Honda specification for clearance and leave them with excess. Have they told you what they are aiming for clearance wise?
It's generally good practice when boring to first measure the pistons that are going to be used, rather than bore without checking.
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I agree with the advice of others here, each piston should be measured and the barrel bored to suit. As Nigel states, you need to be careful of who does the rebore and the tolerance they use. Did you supply them with the Honda tolerance for piston to bore size? Do they do motorcycle rebores and do they have a good reputation?
Having been on the recieving end of an engineer who thought he knew best regards CB250RSA clearances and who ignored the Honda specs without telling me making the clearance far bigger than it should have been (in case it seized with it being air cooled!) and having the bike subsequently blow up on the motorway at 70mph (the wife was riding it and had only just passed her test), I learnt my lesson the hard way!
I can recommend SRS in Sutton, Surrey. Make sure you advise them of the correct Honda specs though.
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Thanks for the replies and advice. They do seem to have a good reputation (SRS engineering engineering in Sutton) and the guy said he went off the Honda workshop manual. He said really to be accurate he prefers to have the pistons. so it's my fault they don't fit . As I said, SRS said if I supplied them he would bore each cylinder individually to the manual specs .
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Pistons and rebores can be a problem with some engineers when it comes to these old girls.
If the pistion is 20% silicone and you rebore to Honda clearances, it will be a tad too tight once the engine is up to temp . The clearance in the Honda Manuel is only for Honda OEM pistons. A lot of the aftermarket ones are out of weight with each other so, they have to be weight matched and matched to the bore ;)
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I think you have the answers. SRS are good especially Michael the owner (tall young guy with a beard). If he works to be the Honda specs (he rebored my CB250RS after its blow up and it now runs absolutely great) and uses Triggers advice you should be fine.
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Always amazed by the combined knowledge of this forum. Thanks again for the advice.
Glad to hear SRS are known here too, thanks Dave.
Lesson learnt for next time.