Setting Piston Ring Gaps for my Honda CB750 Cafe Racer Project Bike + Painting Engine Barrels | 17
Although excited to find that I had a set of Yoshimura pistons for my Honda CB750 Cafe Racer project, I had the problem of finding a different set of barrels and getting them rebored and I also needed new piston rings. It took quite a time, sourcing a barrel having it machined. But I found a better supplier for the piston rings than I ever expected.
Now I have the barrels back I need to get the pistons ready to fit to the engine.
What I used:
IMD Piston and Ring shop: ebay.us/HmdH7r
BLACK E-Tech 400ML Extremely High Temperature Paint: ebay.us/DrPPSA
I got the piston rings from a company called IMD in Cheshire. They supply lots of pistons and rings for all sorts of vehicles. It turned out that they had bought a job lot of NOS pistons, rings and other things from Yoshimura R&D inc back in the eighties. This included piston rings for the 823cc size pistons. I had a great chat with one of the guys from IMD about all of the stuff they had bought, apparently it all came loaded in an old American car which they had shipped to the UK.
Although the pistons are a little larger than the originals, but 3.5mm I don’t think the end gaps would be very different. My research lead me to believe that the pistons were made in the same factory that made the original Honda pistons, and they were made out of the same material. Although they are Yoshimura, these are cast pistons, not exotic forged ones like you might have thought.
When I came to set the end gaps most were just above the minimum clearance, or just needed a little adjusting. You adjust the end gaps with a file, taking a little of each side until you get them to be just above the minimum gap specified. When the engine is running the rings will expand slightly, if the gap is too small they could bind and seize the engine. If the gap is too large the engine will lose compression. And if the gap is way too large the ends of the rings will scratch the bores like mine did.
I did notice that my file was looking a little past its best. In my defence all of my better files are at the other garage where we are working on the E30. I only had to take a little off the rings that needed adjusting, most were just fine.
Mechanically the barrels are fine, and I have already spent a fair amount of time cleaning off the corrosion and old paint. Now I needed to give them a final clean and paint them. I had previously used paint stripper, degreaser and even soda blasted them, but they have been to a machine shop and back so I expect they will have a bit of muck and grease here or there.
I gave them a good wire brushing to scuff up the surface then I used brake cleaner to remove any grease, before masking them up for spraying. I use Xtreme Heat Paint to coat the barrels. When I was happy with the coverage I baked them for an hour in an oven at 160c. This cures the paint properly and should give it a much longer life on the bike.
Overall I am very pleased with the barrels, pistons and rings. Now I just need to get the engine together. I can’t wait.
For more helpful how-to guides and restoration project logs, visit our blog: www.spannerrash.com/
As an Amazon Associate, Ebay Partner and Awin Affiliate, we earn a small commission from qualifying purchases. Some of our links are affiliate links, and if you decide to purchase things through them, we earn a small commission. It costs you nothing but helps us to keep the content coming. Thanks for your support!
#cb750 #hondacaferacer #cb750caferacer