Topic: 1978 CB750F - Metric Mayhem"

[Zaipai]

Zapai said,

Well beauty is in the eye of the beholder.

I thought it was "beauty is in the eye of the beer holder".......

Mick

I think it works in both ways!!!

[Terry in Australia]

F2s seem to be the red headed step child of CBs

Geez, careful mate, the F2/F3's were fragile if not well maintained, but they were still the fastest (yes, faster than the K0's, regardless of what some here might say) and best handling of ALL of the CB750's, with the best brakes by a mile, but they were certainly NOT the "Red headed step child", that has always been, and will always be, the preserve of the "Fugly" K7/K8 and (to a slightly lesser degree) the F/F1. Sure, the F2/F3 had their faults, but their pro's will forever outweigh their con's. Anyway, sorry to interrupt, continue on.

[tweakin]

Great work.  I have a 77 f in the works also.

[Halvin]

Glad to see posts from those who like the F2s.  I acquired my 77 a few months ago after 30 years without a bike.  I learned to ride in '66 on a CA110 and later had a Dream and then, after a Yamaha and a couple of Kaws, had a CL360.  I started looking for an old bike to restore last year but was uncertain about a Honda as a project until I say an add for my F2 on E-bay.  Looks are a very personal thing for all of us and the lines and styling of the F2 are what I was looking for.  After I acquired the bike I found this forum and was soon educated as to what is special about the model.  I have found much useful information and am confident I will hear my F2 run for the first time by sometime in March.  Enjoy reading much of what's on the forum but keep an eye out for CB750F2 posts in particular.  There is lots of expertise to be found here.
Halvin

[scroggins5000]

F2s seem to be the red headed step child of CBs

Geez, careful mate, the F2/F3's were fragile if not well maintained, but they were still the fastest (yes, faster than the K0's, regardless of what some here might say) and best handling of ALL of the CB750's, with the best brakes by a mile, but they were certainly NOT the "Red headed step child", that has always been, and will always be, the preserve of the "Fugly" K7/K8 and (to a slightly lesser degree) the F/F1. Sure, the F2/F3 had their faults, but their pro's will forever outweigh their con's. Anyway, sorry to interrupt, continue on.

Yeah, I've heard horror stories of the black motors before, but I'm hoping everything works out right.
I saw an old road test article from the 70's on the F2 versus the standard K models. The article suggested that the super sport was better in almost every aspect. It was faster in top speed (around 125mph), but the K model still had an advantage on the 1/4 mile. Main reason being because the K is lighter.

[nobody]

In no way was I speaking negatively about the F2, my F3 is the same bike. I love them and think they're awesome, I wouldn't bought one if I didn't. The red headed step child was more related to the fact that I don't see many people building or praising them. They seem to be ignored and shunned by many of the performance years K fanatics. I own a K and a F, neither of which run at the moment. I just wish my F had a title, I need to find a titled frame or parts bike so I can feel confident pouring any more labor or money into it.

[scroggins5000]

In no way was I speaking negatively about the F2, my F3 is the same bike. I love them and think they're awesome, I wouldn't bought one if I didn't. The red headed step child was more related to the fact that I don't see many people building or praising them. They seem to be ignored and shunned by many of the performance years K fanatics. I own a K and a F, neither of which run at the moment. I just wish my F had a title, I need to find a titled frame or parts bike so I can feel confident pouring any more labor or money into it.

Yeah definitely. That's one of the main reasons I wanted a super sport. They're less common, and I wanted something unique.
A friend of mine who has a CB550 cafe was trying to convince me to get a custom tank just for the sake of changing it, and I wouldn't go for it. His argument was that I'm putting so much money into fixing it then why not go with something custom like a Dunstall with some knee dents. It's a good argument, but I think the stock tank is great already. It's long, sleek, and has more of a European feel to it that I really like. The bike is long and slim with straight lines, and I'd like to keep it that way.
Good luck finding a titled frame.

[Terry in Australia]

Yep, F2/F3's are great bikes, my first F2 was very well maintained by it's PO, so apart from an electrical gremlin that drove me insane on wet days, I had no mechanical issues with it at all, even though it had done 50,000 miles. I had no idea that they had problems until I bought my current one, and with the help of this site, learned all the problems associated with the top end of the engine, it's only fault.

My F2 is now sporting a K6 top end, (cylinders, pistons and head) albeit with the F2 cam and carbs, and so now it's as "bullet proof" as any other CB750, but with the F2's beautiful looks, brilliant brakes, and excellent performance. Cheers, Terry.

[nobody]

That thing is gorgeous, Terry.

[Terry in Australia]

Thanks mate, I am kinda proud of it.

[nobody]

As you should be.

[scroggins5000]

I'm still waiting to find out from the shop exactly what size pistons I'll need. I'm on the back burner because they've been swamped.
In the mean time, I've been searching around for STD and OS pistons just to get an idea of where I will order from and how much it will cost. Bike bandit has the pistons, but does not carry the rings anymore. They are out of stock. I think I found a honda dealer that carries both and the pistons/rings and are actually cheaper than bike bandits. Hopefully when I find out exactly what I need, they have them 4 of them in stock. If I can't find what I need, then I may have to go with a big bore kit... I found a good deal on one from Wiseco. I don't want to bore it out because then I would need to pay to have it bored, plus also buy a new jet kit. It's just extra time and money that I don't really want to spend. I'd rather keep it close to stock anyways, because I'm not going to race it or anything...
Anyone have any ideas on where to shop for STD and OS pistons for a 1978 CB750F2?

[tweakin]

http://www.westernhillshondayamaha.com/

I was able to get STD rings from these guys.  Talk to Terry or ED in vintage parts.

If the part is still out there they can get it.

[scroggins5000]

Ok, here's the deal. I've been doing some research on 836cc kits in an F model, and I've found a lot of people talking about it. However, I haven't found anyone that's done it. I've heard conflicting things too about what does and doesn't work and what will and won't fit.

The Wiseco 836cc kit (part# K836) fits all 69-78 CB750 K & F models... But here's the deal: 78K and 78F stock pistons have different dome shapes and have different compressions. So, how does this one kit work well for both engines? Ok yeah it fits, but will they run WELL in a F model? Anyone here have an F with this kit installed that can offer some advice?

Cycle Xchange offers an 836cc kit that specifically states it is for the F model, but it looks the same as the Wiseco, and has the same specs.

[Flying J]

dyno man has a F kit. It is different.
http://dynoman.net/bikepages/F2/pistons.html

"Kit comes complete with pistons, rings, pins, clips, and head gasket.

As the 1977-78 Honda CB750 F2 has an 18% larger combustion chamber to compensate for the larger valves, through the years many people have installed the standard 836 (ex: Wiseco K836) kits for the 69-76 engines only to discover that the compression was too low to give them the extra power that they were after.

Dynoman now offers our new custom 836cc piston kit for the F2. It has the correct dome to raise the compression to a true 10.26:1. This kit has the same compression ratio that the 1969-76 models have with the K836 Wiseco kits.

These new pistons are state of the art diamond cut on CNC machines from 2618 aluminum forgings. This is the same alloy used in many prostock pistons. This process makes them lighter than some of the cast pistons used in the 70s, but much stronger. They also come with a brushed dome to smooth any sharp edges.

They have shorter piston pins for less weight and large valve pockets for the 31 and 34mm valves used in the F2 engines.

They are the same bore size as the standard Wiseco K836cc kit, so they are a drop in for any F2 with the standard K836 Wiseco kit already installed.


 "

[scroggins5000]

dyno man has a F kit. It is different.
http://dynoman.net/bikepages/F2/pistons.html

"Kit comes complete with pistons, rings, pins, clips, and head gasket.

As the 1977-78 Honda CB750 F2 has an 18% larger combustion chamber to compensate for the larger valves, through the years many people have installed the standard 836 (ex: Wiseco K836) kits for the 69-76 engines only to discover that the compression was too low to give them the extra power that they were after.

Dynoman now offers our new custom 836cc piston kit for the F2. It has the correct dome to raise the compression to a true 10.26:1. This kit has the same compression ratio that the 1969-76 models have with the K836 Wiseco kits.

These new pistons are state of the art diamond cut on CNC machines from 2618 aluminum forgings. This is the same alloy used in many prostock pistons. This process makes them lighter than some of the cast pistons used in the 70s, but much stronger. They also come with a brushed dome to smooth any sharp edges.

They have shorter piston pins for less weight and large valve pockets for the 31 and 34mm valves used in the F2 engines.

They are the same bore size as the standard Wiseco K836cc kit, so they are a drop in for any F2 with the standard K836 Wiseco kit already installed.


 "

Finally, something that makes sense. This looks the way to go. Thanks.

[Freaky1]

I saw that on dynoman's web site also and am very interested, please keep us informed scrogg I'd love to know how this worksout.

[scroggins5000]

I saw that on dynoman's web site also and am very interested, please keep us informed scrogg I'd love to know how this worksout.

Will do. Gotta see if my buddy can get it through the shop and hook me up with a discount. I'll keep everyone updated on the progress.

[scroggins5000]

I've decided to fight temptation on the 836cc, and I'm sticking with stock. Basically the main reason is that I want it to be as reliable as possible. It doesn't make much sense to put a big bore kit in my bike, because I don't want to upgrade the entire engine. It would be nice, but I just can't afford all that high performance stuff. It should probably be completely built for racing, or completely built stock. Not mixed... I'd rather not take the risk, and play it safe.

[scroggins5000]

Price is a factor too. I'm saving up for my wedding in January, and I need to keep as much cash in my pocket as possible.  Another reason I'm gonna go stock, and not invest in parts that don't need replacing to upgrade the entire motor. Like new cams, cam chain etc.

I should also mention the other stuff we found out needs to be fixed/replaced on the motor:

The head gasket seal was warped slightly, and will be machined down. This was probably the only major flaw with the head, and is an easy fix for the shop. The cylinder walls are in pretty good shape. A couple of the spark plug holes need to be re-threaded, because like half of the threads are missing. It looks like there was some moisture build up in the engine that caused this. It probably also caused the pitting in the valves (and the pistons), so the valves need to be replaced. The valve guides need to be replaced too. One was worn down pretty bad. I am also going to replace the valve springs, and retainers as a preventative measure.

[Flying J]

cycle x had the best prices on valves for the f motor that i could find.

[scroggins5000]

cycle x had the best prices on valves for the f motor that i could find.

Yeah, they are about $200 cheaper than Honda OEM. $159 (CycleX) vs $355 (OEM). I'll most likely go with these..

Here's pricing I've found of the rest of the stuff I need:
(4) .5 OS Pistons w/ rings, pins, and clips - about $460
Inner and outer valve springs and retainers - about $155

I think I've already got valve stem seals in my gasket set, If not then they're cheap. Like $10 or less. I think I can get nice valve guides through the shop too..

[scroggins5000]

My friend Aaron who is helping me work on the bike decided he wants to start an LLC for working on bikes called "Metric Mayhem". Being a graphic designer, I made a logo for him (and some other artwork), and I've decided I want to use the logo to make some new custom badges to go on the tank. I'm going to try and get them 3D printed in plastic (I may have them done in stainless steel, but it may be too expensive for me). This guy I went to school with said he would help me with converting the art into 3D files for printing. I still need to work on getting the sizing correct, but here's the flat artwork. I wanted them to look similar in shape to the stock Honda super sport badges. I haven't seen anyone do this yet, but I think it will work out well.

[afastman]

Would look great wither CNC milled our of metal or laser etched.  Either one is extremely simple to convert to the appropriate file type.  Lasers can even read EPS files. 

[Zaipai]

For what it is worth I really like that logo!!

.: Scott :.