Author Topic: 1978 CB750F - Piston Rings (Read 4693 times)

cgarbe · « **on:** April 21, 2015, 01:20:58 PM »

Hey guys...I need some help.

Having the top end of my 1978 CB750F rebuilt due to low compression. My mechanic ordered a set of rings from a bike parts website and when they arrived they didn't fit the domed pistons and he said after further research the rings are no longer made. Has anyone else run into this problem? Does anyone know where to buy new standard bore piston rings (Part #13011-410-601) for a 1978 CB750F? If I can't find them my only other option is upgrading to the big bore 836 kit. Thoughts?

Thanks guys!

flybox1 · « **Reply #1 on:** April 21, 2015, 01:52:03 PM »

i bought some a while back for my F3. let me look it up...

flybox1 · « **Reply #2 on:** April 21, 2015, 02:02:31 PM »

I bought my sets from cb750supply.

doesnt look like they have any, but i did find them here...

http://parts.southernhonda.com/p/Honda__/RING-SET--PISTON-STD/54981922/13011-410-601.html

Wobbly · « **Reply #3 on:** April 21, 2015, 02:10:14 PM »

Only one left--which won't do you any good:
http://www.cmsnl.com/honda-cb750f-750-super-sport-1978-usa_model7240/ring-set-piston_13011410601/

Wobbly · « **Reply #4 on:** April 21, 2015, 02:13:21 PM »

Wait, there is more:

http://www.ebay.de/itm/Satz-Kolbenringe-STD-CB-750-F2-CB750-F2-Bj-1977-1978-13011-410-601-/191490103286?pt=LH_DefaultDomain_77&hash=item2c95b317f6

70CB750 · « **Reply #5 on:** April 22, 2015, 03:34:16 AM »

I bought mine from this guy:

http://www.ebay.com/sch/honda-cb350/m.html?_nkw=&_armrs=1&_ipg=&_from=

I think it is an ebay shop of this guy:

http://metric-cycle-parts.com/index.php?main_page=index&cPath=1&zenid=5c9ae4e318cd5eeebbe1671823489555

BUt seems like he is all out now

cgarbe · « **Reply #6 on:** April 22, 2015, 06:10:53 AM »

Thanks for the help guys! I actually ordered 4 sets from the southern honda place flybox1 found! Thank you all very much...hopefully they fit this time. : )

koendd · « **Reply #7 on:** April 22, 2015, 11:17:50 AM »

any more there? And how much did they cost?

Looking for a set of 4 for my F2 as wel...

cgarbe · « **Reply #8 on:** April 22, 2015, 12:07:28 PM »

Funny you should ask...I just got an email from the supplier i ordered them from saying they actually don't have any and gave me a refund. So...i guess I'm back to searching for other suppliers.

martin_uk · « **Reply #9 on:** April 22, 2015, 12:59:41 PM »

Found this info from a few years back.

http://forums.sohc4.net/index.php?topic=98890.0

cgarbe · « **Reply #10 on:** April 22, 2015, 02:10:06 PM »

cb750supply has them on order but said it would take 2-3 months to receive them...so now I'm leaning towards an 836 kit. Any suggestions on where to get this kit and which kits are good? I know there is one floating around on ebay. Thanks all!

flybox1 · « **Reply #11 on:** April 22, 2015, 03:40:05 PM »

Quote from: cgarbe on April 22, 2015, 02:10:06 PM

cb750supply has them on order but said it would take 2-3 months to receive them...so now I'm leaning towards an 836 kit. Any suggestions on where to get this kit and which kits are good? I know there is one floating around on ebay. Thanks all!

there is a thread for cheap ebay 836 kits. several have used them, with good results. ill see if i can find it.
i believe the ebay seller name is cruisin image

here it is...http://forums.sohc4.net/index.php/topic,89779.0.html

koendd · « **Reply #12 on:** April 23, 2015, 06:37:25 AM »

U can go for that 836cc kit but then you loose compression (flat top piston vs. domed top...) in an K7-F3 engine

Davidov · « **Reply #13 on:** April 23, 2015, 07:39:11 AM »

I used the set from CB750supply.com, but it looks like VintageCB750.com has them as well. Not sure if they are in stock, just email. Their customer service is outstanding.

Ring Set OEM Ref. #13011-392-004 (Std.)
http://www.vintagecb750.com/products/4/engine/75/pistons-ring-sets

flybox1 · « **Reply #14 on:** April 23, 2015, 07:45:15 AM »

Quote from: koendd on April 23, 2015, 06:37:25 AM

U can go for that 836cc kit but then you loose compression (flat top piston vs. domed top...) in an K7-F3 engine

easily rectified when getting your head decked

flybox1 · « **Reply #15 on:** April 23, 2015, 07:48:39 AM »

Quote from: Davidov on April 23, 2015, 07:39:11 AM

I used the set from CB750supply.com, but it looks like VintageCB750.com has them as well. Not sure if they are in stock, just email. Their customer service is outstanding.

Ring Set OEM Ref. #13011-392-004 (Std.)
http://www.vintagecb750.com/products/4/engine/75/pistons-ring-sets

so the 392 piston rings fit the 410 pistons? I thought the ring gaps were different $:-\$

cgarbe · « **Reply #16 on:** April 23, 2015, 08:55:28 AM »

It looks like the Dynoman pistons are dome shaped.

http://www.dynoman.net/engine/pistons/custom.html#F2

Btw, I keep running into the F2 and F3 question. Is my 1978 cb750f an f2 or f3?

70CB750 · « **Reply #17 on:** April 23, 2015, 09:04:24 AM »

F3 officially does not exist, right? Just a way to distinguish year 1978 from 77 F2.

http://www.motorcyclespecs.co.za/model/Honda/honda_cb750f_78.htm

flybox1 · « **Reply #18 on:** April 23, 2015, 09:07:08 AM »

As I understand it....
75 F0
76 F1
77 F2
78 F3
The F0/1, 392 heads/pistons, round top carbs
The F2/3 typically have the 410 heads/pistons, PD carbs, cam and valve changes as well.
Engine VIN verification is advised. engine swaps and production overlaps are common.

flybox1 · « **Reply #19 on:** April 23, 2015, 09:08:29 AM »

Quote from: 70CB750 on April 23, 2015, 09:04:24 AM

F3 officially does not exist, right? Just a way to distinguish year 1978 from 77 F2.

http://www.motorcyclespecs.co.za/model/Honda/honda_cb750f_78.htm

it is referenced in your link, but i dont know if it has any mechanical or design differences from the F2

"Pottering along at a steady 30 mph (33 indicated) the F3 returned a best figure of 80 mpg"

70CB750 · « **Reply #20 on:** April 23, 2015, 09:10:09 AM »

Quote from: flybox1 on April 23, 2015, 09:08:29 AM

Quote from: 70CB750 on April 23, 2015, 09:04:24 AM
F3 officially does not exist, right? Just a way to distinguish year 1978 from 77 F2.

http://www.motorcyclespecs.co.za/model/Honda/honda_cb750f_78.htm
it is referenced in your link, but i dont know if it has any mechanical or design differences from the F2

"Pottering along at a steady 30 mph (33 indicated) the F3 returned a best figure of 80 mpg"

I see, thanks! Is 410 unique F3 head?

flybox1 · « **Reply #21 on:** April 23, 2015, 10:01:39 AM »

Quote from: 70CB750 on April 23, 2015, 09:10:09 AM

Quote from: flybox1 on April 23, 2015, 09:08:29 AM
Quote from: 70CB750 on April 23, 2015, 09:04:24 AM
F3 officially does not exist, right? Just a way to distinguish year 1978 from 77 F2.

http://www.motorcyclespecs.co.za/model/Honda/honda_cb750f_78.htm
it is referenced in your link, but i dont know if it has any mechanical or design differences from the F2

"Pottering along at a steady 30 mph (33 indicated) the F3 returned a best figure of 80 mpg"

I see, thanks! Is 410 unique F3 head?

410's should be on all F2/3's
Im sure the more seasoned F'ers can answer more specifically, but the F's went from a flat top piston (stamped 392 on the piston and head) for '75/'76, to a domed piston and head (410) for the '77/'78 F2/3. (valve sizes changed for 77F/78F, too)
The 410 domed pistons wont work in a 392 head, as they'll contact the valves, but 392 pistons, with their flat tops, can be used in 410 heads. This lowers CR, which is easily increased back close to stock with a decking of the head.
I read somewhere on the forum the ring cutouts, and ring thicknesses on the 392 pistons are slightly different than the 410 pistons, which might make their use on the 410 pistons less than ideal...Ive tried, but i cant find the thread for reference. $:-\$

KRONUS0100 · « **Reply #22 on:** April 23, 2015, 03:50:11 PM »

THE 392 (late 1/2 of 76 F model) rings work. thats what im running gin my 78 F3 motor. 7500 miles so far since i put the motor together, no issues with compression o roil useage

Wobbly · « **Reply #23 on:** April 23, 2015, 10:07:01 PM »

Quote from: KRONUS0100 on April 23, 2015, 03:50:11 PM

THE 392 (late 1/2 of 76 F model) rings work. thats what im running gin my 78 F3 motor. 7500 miles so far since i put the motor together, no issues with compression o roil useage

They were used up to serial number: 2612797

Jerry Rxman Griffin aka MuthaF'er · « **Reply #24 on:** April 23, 2015, 10:12:37 PM »

The 392 and 410 rings should be the same. As mentioned the 392 appeared late in the 76 F1 year. Prior to that the F0 and F1 used 300 rings.

News:

Author Topic: 1978 CB750F - Piston Rings (Read 4693 times)

Wobbly

Wobbly

Wobbly