Curious engine, low compression


Re: Curious engine, low compression

Postby Crazy Canuck » Thu Nov 28, 2019 7:58 pm

Any updates to this?
Forrest Miller :thumupp:

Honda CBX 1000- "A cosmic haymaker of a motorcycle"
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Re: Curious engine, low compression

Postby CBX1000chris » Mon Dec 02, 2019 6:20 am

Hello Herdygerdy and Crazy Cannuck,

To be honest I didn't look at the ring orientation on all of the pistons but the ones I did check were correct although the gap alignment was way off the recommendation from Weisco. As I think I mentioned early on this isn't my bike, it belongs to a friend who has built a special using a Metisse rolling chassis, not one of the early motocross chassis, (Steve McQueen said "THIS RIG IS THE BEST HANDLING BIKE I'VE EVER OWNED"), but the later MK5, see link below. On the subject of Steve McQueen, it might be worth watching Guy Martin's Great Escape next Sunday (8th December).

https://www.motorcycleclassics.com/clas ... cz12mazbea

Imagine the above with a CBX motor fitted, very nice. I wish I could insert a picture or two (not sure how to do it anymore). The exhaust goes 3 into 1 then 2 into 1 under the seat and out through a hole in the tailpiece. I think Lord Flashheart would have said "Well, well, well, if it isn't little Bobby Parkhurst...saucier than a direct hit on a Heinz factory!"

Anyway, I'm waffling. I took the head and barrels to the work shop. Both the head and the barrel have some warpage and the number three and four cylinders are scored, enough to present a problem. So I'm weighing up the options and decided we could:

1. Get a replacement barrel and bore it to suit the new pistons that were fitted to the bike
2. Over bore to the next size and get new pistons
3. Fit new liners to the number 3 and 4 cylinders

At this point I though it best for the owner the talk the workshop and and discuss the options (money). They have decided to fit new liners and use the existing (as new) pistons. They agreed to lightly hone the other cylinders and I must check to see what they decided to do about the warpage. I did ask a question earlier about how much could be skimmed from the head and barrel before squish became an issue. I did have one reply from daves79x, thank you Dave.

If you have to skim a lot from both head and barrel can you skim enough for the reduction in squish to be taken up by a second base gasket? Until recently I was racing late model TZ250s and had a wide range of Yamaha base gaskets to vary head volume. Sometimes I'd run two gaskets to get the volume I wanted without issue and TZ base gasket sealing is slightly more critical than CBX!

The bits are still in the workshop, as soon as they're ready I'll build it back up and let you know the outcome.
Have a great day everyone,
Chris.
p.s. I probably ought to learn how to post an audio.........
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