Topic: 78 Supersport build

[Bodain]

Well this 78 Supersport build is degrading fast.... It all revolves around the engine.

First I have these problems with the head, then just when I think I have all this squared away I need a new set of rings. First I buy a set of 69 - 76 standard rings thinking since the bore is identical they will work..    How wrong can I be...  The 78 rings are thinner.....

THen I try to find a correct new set of rings for the 78 F.... All the Honda dealers say they are unavailable. David Silver Spares might have them... I order... Fortunately they double check that what you order is correct. They're reply was consistant... I ordered the wrong part. The rings are not available....

I'm quickly learning you do not want a 78 F engine, but this is getting expensive.... <GRIN>

Now for the questions... I have a 1978 Supersport. I thought it was an F2. Apparently it's not.
Can someone explain the F1, F2, F3 designation relative to the Supersports. Thought I understood it by reading the FAQ.


Since I can't get new rings for this...I'm trying to decide the best course of action..

1...  Entirely different engine.
2...  K series top end

[bryanj]

Need the complete engine and frame numbers to tie up what it is

[Lumbee]

...are you sure you need rings?  What was the compression like before tear down?

...best compilation of engine timelines I've found is here:

http://hondachopper.com/modifications.html

[Wheelhorse77]

http://www.tradekey.com/product_view/id/72772.htm

http://www.tkrj.co.jp/product/m-piston-ring.html#h

It would probably be cheaper to do an 836 kit at this point LOL. It seems the F is really earning it's F title.

[dusterdude]

if you send a piston to a ring manufactuer,they will make you a set of rings.

[scondon]

   '78 750F is designated a F3 in the US. There are some minor cosmetic changes and the rod bolts are different compared to the '77 F2. Also, the jet needles do not have clips for changing positions. The 77-78 750F's are very different than the F and F1, primarily in the engine as you are finding out.

    I put a K8 engine in my F3 when I first bought it. The K8 engine had the studs for mounting the exhaust and it also utilized the 630 chain. Later, I rebuilt the engine with 836 pistons using the K8 top end and F3 bottom end.

    Buzz at Dynoman is currently working hard at making available performance parts specifically for the F2-F3 "Black Motor". He has dropped the price of his replacement valves and now offers 836 pistons and performance springs. He knows the ins and outs of this motor and may be able to provide you with info on getting rings for the stock pistons, or maybe not but it wouldn't hurt to ask.

[Bodain]

...are you sure you need rings?  What was the compression like before tear down?

...best compilation of engine timelines I've found is here:

http://hondachopper.com/modifications.html

<GRIN> Yea I'm pretty sure it needs rings. The original problem was the head. Since I had the head off, thought I might as well pull the cylinders in preparation for proper cleaning and paint. Point note! Prior to pulling the head I did a compression check across 3 cylinders. It was all very good at 140 to 150 PSI...

When I actually pull the cylinders I notice the rings are frozen in the slots and not moving across 3 of the 4 pistons. So I proceed to free them up... The are really frozen in the piston groves. Naturally several rings break in the process of removing them...

[Bodain]

Ok... Seems there is still another option for unobtainable 78 CB 750 Supersport rings.

What if you had a set of standard CB 750 rings 69-76... I do.... The only reason they won't fit the 78 F piston is they are slighly thicker. What if you had a machinist who could slightly widen the two ring grooves on the 78 piston to accept the older rings???

Hmmmm    Now you would have an engine that you could get rings for!

I'll let you know how it turns out. I'll be taking those piston and rings to my machinist friend.

[mikedialect]

   '78 750F is designated a F3 in the US. There are some minor cosmetic changes and the rod bolts are different compared to the '77 F2. Also, the jet needles do not have clips for changing positions. The 77-78 750F's are very different than the F and F1, primarily in the engine as you are finding out.

Oh my! I thought I had an F2 all along... and I guess I have an F3??? all 78's were f3's?

[mazingerzeca]

I think that they have the rings you need, if you rebore to 0.25 or keep standard bore.
http://www.cmsnl.com/honda-cb750f-750-super-sport-78-us_model7240/partslist/E++15.html

[edbikerii]

Does Total Seal list gapless rings for your bike?  If they don't already have them, they will make them for you per your piston specs.

[scondon]

   '78 750F is designated a F3 in the US. There are some minor cosmetic changes and the rod bolts are different compared to the '77 F2. Also, the jet needles do not have clips for changing positions. The 77-78 750F's are very different than the F and F1, primarily in the engine as you are finding out.

Oh my! I thought I had an F2 all along... and I guess I have an F3??? all 78's were f3's?

   Only in the US, Mike. It's easier to refer to it as a F2 since most people refer to it as such. There are just a few differences between F2 and F3 bikes that might come up when trying to source parts and that is usually the best time to make the distinction.

[jtb]

Bodain,

Mike Rieck found rings for my '78 F2 somewhere in Canada.  Mike, do you remember where?

[Bodain]

I think that they have the rings you need, if you rebore to 0.25 or keep standard bore.
http://www.cmsnl.com/honda-cb750f-750-super-sport-78-us_model7240/partslist/E++15.html

They too say they are unavailable for standard bore, but yes looks like they have piston overbore kits. I had already been on Weisco site. Interesting the standard 836 kit Weisco offers fits 69 - 78....

[Jerry Rxman Griffin aka MuthaF'er]

Someone mentioned Total Seal. Send them your pistons and if they can't find rings they will cut the pistons for rings they already make (as opposed to making rings to fit) . Approx $20 per piston + rings.

[TieRBuoYs]

About 2 years ago, I was able to obtain 3 sets of 0.25 rings for my F3 from CMS. Luckily, I found another set from a Honda dealership out of Cincinnati, Ohio. You could start there.

Depending on the help your local Honda dealer is willing to provide, they could put out a search across all North American dealerships looking for any parts you need.

[Bodain]

And the answer for those unobtainable 78 Supersport rings is..............



Shot at 2007-07-14

The standard bore rings for a 69 - 76 are a perfect except, the two upper rings are about .012 thicker than the standard 78 rings. Machinst friend removed .012 from the two upper ring grooves.
Rings for this 78 750F are now available everywhere.

[MRieck]

Bodain,

Mike Rieck found rings for my '78 F2 somewhere in Canada.  Mike, do you remember where?

I got them through my regular Honda dealer John. One of the Canadian members gave me the part #. There are plenty available....they are under a different part #. I believe after 75 all the pistons used the thinner top ring. The part # is in a thread here....you'll have to search.

[Bodain]

After being beat up considerably on the 750F.... I aquired a 78 750 K head off of Ebay...

I expected to see the smaller valves. Indeed the valves are smaller. The intake inserts are also slightlhy smaller, again I can adapt to this.... So my intention is to use a 78 K head ontop of 78 F cylinders. Those two items mentioned are the only real difference I can see...

So now it's time to put it back together...... For those of you with far more experience than me on 750 engines.....

The third set of studs from the outside on each side have some recessed holes around the stud. I don't recall any rubber seals being there. There are 4 total..Clymers is about useless..
Does anything go in those recessed holes???



Shot at 2007-07-19

[Lumbee]

...I've done 2 F rebuids and I always get confused at this point.  U'r right that the manuals never seem to help.  I just looked at the k7/f2 shop manual, and from the picture they have there is nothing in the 3rd set of studs..

[Wheelhorse77]

Has anyone had problems with reusing old studs and having premature head gasket issues as a result?

[Lumbee]

...I think anyone who has messed with these old 750's has had head gasket issues at one time or another!     When you say reusing old studs, do you mean just not replacing studs when a rebuild is done?  I've never replaced any studs.  I've rebuilt a handful of motors and had some leak, and some not.  I'm sure purchasing the tougher studs which allows higher torque would give you a better shot and keeping oil off u'r pant legs, but I've never went so far as to shell out the ducks for new studs.  I guess I'm a masochist, er uh...machinist!   

[scondon]

Bodain, read this thread....

http://www.sohc4.us/forums/index.php?topic=17622.0

[Wheelhorse77]

...I think anyone who has messed with these old 750's has had head gasket issues at one time or another!     When you say reusing old studs, do you mean just not replacing studs when a rebuild is done?  I've never replaced any studs.  I've rebuilt a handful of motors and had some leak, and some not.  I'm sure purchasing the tougher studs which allows higher torque would give you a better shot and keeping oil off u'r pant legs, but I've never went so far as to shell out the ducks for new studs.  I guess I'm a masochist, er uh...machinist!   

Right, using the 30+ year old studs. I was wondering if they lost their torque holding capabilities prematurely, but I guess not if no one seems to replace them and has no ill outcomes from not replacing them.

[Bodain]

Bodain, read this thread....

http://www.sohc4.us/forums/index.php?topic=17622.0

Thanks for the tip.. Interesting reading... Generally what I'm looking for... But still some inconsistancy...

The conversation refers to F2  which should be 78 SuperSport. Seems to be much confusion around F2 and F3..  Still not certain! The conversation said the F2 didn't have cutouts for valve clearance in the pistons. Mine does.

Still I'm sitting here comparing the 78K head to the 78 F head... I do indeed have domed pistons, but the pistons have cutouts for valve clearance. The F valves are larger.

The hole pattern on the two heads is identical in all respects....

Well it seems I got nothing to loose. I'm gonna bolt the K head up to my 78 F cylinders, install the cam and adjust clearance. Then slowly turn the engine over.