New Pistons

[Jenya79]

Hi all,

I am doing a top end on my 1976 CB750k and am looking for a set of stock pistons. I have seen a set for as cheap as $109 from the parts dealers like 4into1, for $209 from IMD (imdpistons.com/products/honda-cb750-sohc-300-piston-kits-4), and ones in the $500 and above range. Are the cheap ones a "run the other way" kinda thing? Is the IMD set sufficient in quality? Not aiming to change the bore or compression.

P.S. Before anyone asks, I had intended to only do the head gasket and the whole top end came off when I started removing the head. Furthermore the original pistons have a whole bunch of carbon built up so I thought I might as well do that job as well.

Cheers and thanks in advance

 

[dirtdigger]

If the pistons measure fine and no wear you can just clean the carbon off with a wire wheel or soda blasting or similar means. But the stuff from 4into1 is okish for stock setup but I would prefer actual honda parts if it was mine doing a stock rebuild. You will need to at least have the cylinders deglazed if they measure straight. If there is some wear you should bore the cylinders and at that point the 836 kits are just as reasonable as stock bore pistons. Cyclex does piston and cylinder kits ready to bolt on which is a good option.

 

[Jenya79]

If the pistons measure fine and no wear you can just clean the carbon off with a wire wheel or soda blasting or similar means. But the stuff from 4into1 is okish for stock setup but I would prefer actual honda parts if it was mine doing a stock rebuild. You will need to at least have the cylinders deglazed if they measure straight. If there is some wear you should bore the cylinders and at that point the 836 kits are just as reasonable as stock bore pistons. Cyclex does piston and cylinder kits ready to bolt on which is a good option.

Thank you, that helps!

 

[hinksy]

jenya if all measures up good and you decide to keep and clean the old pistons , just go a new set of rings with a rehone and gaskets

 

[Jenya79]

jenya if all measures up good and you decide to keep and clean the old pistons , just go a new set of rings with a rehone and gaskets

Thanks, I am now thinking this is the way to go.

As far as re-honing, I assume this is a machine shop job? Or is this doable at home?

 

[dirtdigger]

Your best result will come from a machine shop but you can do it at home with a hone but if you dont get the crosshatch close to correct angles you can get oil usage. Maybe post some pictures of your pistons to see what we think about the condition.

 

[Jenya79]

So, the pistons actually look pretty decent now that I have the cylinder block fully off.
They’ll just need a good cleaning. The cylinder sleeves themselves actually don’t look too bad. They’re smooth and I don’t feel any inconsistencies. Should I still give them a hone since I’m going to put in new rings?

 

[dirtdigger]

Yes you have to hone with new rings. What do the skirts of the pistons look like? I would measure the piston to cylinder clearance. Looks good means nothing if the clearance is to wide. The top of the piston can look perfect but the skirts are trash. same with piston pin bore and even ring land wear and clearance. you can check the old ring end gap and get a good idea of wear.