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| tolis |
 Posted: Wed Aug 30, 2006 6:42 pm |
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Rookie
Joined: 28 Aug 2006
Posts: 1
Location: Athens, Greece
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Hi all,
new to this forum, you guys have an excellent and very informative site. When i get my own space to rebulid my cb750 cafe racer i will surely take advice from this site.
But for now i have a bit of a silly question.
I am replacing my cylinder block with one that has high domed pistons marked with 392. I think 392 makes this an F model right? What year though i don't know, i don't have an engine number. Can anyone plese tell me what is the right part number for a set of standard piston rings? Is it 13011-392-004 or is it 13011-300-024. Partsfish have the former number for the 1977-78 models and the latter for the 76 model. Which one had the high domed pistons please?
Also, i would like to replace the cylinder gasket with maybe a copper or aluminium one (anything stronger and better than the original one). Does anyone know where to find one?
Thanks
Chris |
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| Satanic Mechanic |
| Posted: Fri Sep 01, 2006 4:30 pm |
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Moderator
Joined: 04 Sep 2005
Posts: 309
Location: Munich, Germany
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Hi Chris,
392 is the model number for the CB750F, CB750F'76, i.e. the early Supersport model, aka F1. (see http://www.satanicmechanic.de/partnos.shtml for part numbers and models).
That said, 13011-392-004 should be the correct part number. OTOH, the high domed pistons were only used in the 77/78 Supersport models, the F2 and F3.
Can you identify your pistons in that picture:
http://www.satanicmechanic.de/board/viewtopic.php?t=93
The right piston is from an '78 F2 model. If you can identify your pistons there, i can look up the exact numer for you.
Copper head gaskts are available from Cometic:
http://www.cometic.com/
Hope that helps! |
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| RxmanGriff |
| Posted: Sun Sep 03, 2006 4:08 pm |
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Junior member
Joined: 28 Jul 2006
Posts: 26
Location: Colorado Springs, CO, USA
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A 392 piston came out first on the 75 CB750F which is identical to the 76 CB750F1. The 77 & 78 CB750K use virtually the same base engine as the first F's (as opposed to the earlier K's) with a few differences. The pistons for these are also listed as 392. I have a 75 F bike and a 78K engine. The part numbers for the pistons are:
13102-392-000 for engines up to 2551567
13102-392-020 for engines 2551568 and up
The rings are listed as
13011-300-024 for the earlier 392 engines up to 2551567
13011-392-004 for engines 2551568 and up.
I can not determine how to attach an image or I could show you the differences.
The earlier part number piston is virtually flat compared to the shape of the later part number but slightly rounded upward with larger valve pockets. The later part number piston has very small valve pockets with a dome covering most of the piston top except a circular area around the piston for the valve pockets. The piston height appears to be the same on both. I measured both to be 56mm. My assumption would be the earlier pistons have higher compression. If someone can explain how to attach a picture I will post it. Otherwise get me your email address and I will send it. The F2 & F3 have 410 pistons with 13011-392-004 rings. I MIGHT be able to measure rings if necessary.
I looked at Axl's piston pictures. His K picture appears to be identical to my 78K pistons. My 75F 392 piston looks like neither.
Hope this helps more than it confuses.
Jerry |
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