Honda-SOHC

Yeah, I have done it. Sacrilige! But I had to do it. For a number of reasons.

I asked the wise and all knowing forum members for suggestions, and received a load of help from a number of members. I thank you all!

Ultimately, I got chatting with Archmill, and he was able to supply me with a kit to do the work. I liked the look of it, and I liked the price of it. Kits were available from the US at quite high cost, made worse by import taxes and eye watering postsal charges. Was going to cost me £80 foor postage from one well known supplier. On top of the £190 +VAT and import duty. So I took the plunge and orderd a kit from Archmill.

This is what I got in the post, well packed and lost for a week or two by my local post office. But, eventually...it surfaced and landed on the mat., With a thud. It;s quite heavy!!



It's basically 8 steel bungs, 4 threaded stainless M12 rods, 8 nuts and washers and 2 flat plates threaded for dome headed screws along with washers and nuts.

Step 1 is to break out hte hacksaw...and there is no turning back now! Detailed instructions were supplied as to how to do this, and Arch also gave me some additional help with the best locations to cut and the measurements to get best results. Can;t thank him enough for the help he gave me when I got stuck..but more of that later!

He suggested using a jubille clip to get the cuts square, and it does work. Gives a clear guide edge to follow.


I drilled and bolted on the 2 plates to rejoin the gussets before I cut them, so I can located them and use them as a datum for reassembly. I slapped the plates on outside for now. They go inside when it's all done so they don;t show so much.

The instructions made it VERY clear that you need to assemble and bolt up all the parts before welding. It ensures that all the threads are correctly positioned and all lined up the same. If you don;t, you could end up with a plug fractionally off, and it;s not going to bolt up. That would be bad. Very bad. So it was all dry-fitted and positioned exactly where I wanted it before any metal gluing began!


I had picked up a new welder recently, which has a bit more 'guts' than my old one, and this was my first real use aside from a couple of tests. It;s not the prettiest welding...but it glued the metal together, and I was able to confirm I had decent penetration.

Still...a soft pad and some elbow grease makes the welds look better. Honest!

With the welding all done, I dismantled the thing and began to clean up the residue. I'm using a gasless MIG, which is OK, but it leaves a lot of residue behind to clean up. As well as a few bits of weld spatter. No matter, I thought, soon get all that cleaned up.

Then...it hit the fan.

You basically use the paied nuts as a jam-nut to wind out the threaded bar and remove the centre section. 3 came out lovely. One...did not. It just locked up solid. I was able to wind it one way fine....but it would not come back! With much jigger-pokery, I removed the centre section again, but was left with the threaded bar jammed solid into the bung and it was NOT budging. I tried threats, swearing and ultra violence...and no joy. My joy at seeing the bungs all welded and lovely sank like the Titanic.

I broke out the saw, and was able to chop another few mm back and remove the bung. Which..incidentally...allowed me to see my welding had indeed penetrated through and the little piece of tube was firmly attached. and is still...to this very day...one with the bung! As is the threaded bar. I ground flats on it to hold it in the vice and leant on it with a breaker bar, nope. That thins is in there. Most likely, it has picked up some debris from inside the tube, and that rode up the threads to jam them tight. You can only apply so much force through the jam nut, and that was me done.


A despairing e-mail to Arch, and the man came up trumps again. He took pity on my poor soul, and sent me a rep[lacement bung, a spare piece of threaded bar and some replacement nuts for the ones I had butchered horribly.
If I ever meet him..I owe him severl beers! Wouldn't even take postage money. Absolute hero!

Busted out hte welder again, and with the centre section back in place ( after REALLY cleaning out the tubes...which had debris that had to have come from Mr Honda judging from the state of it ) I was back in business! I took a slice of frame off a chopped out piece to replace the lost 5mm, and to line it all up evenly. The bung was plenty long enough and with an extra ring of weld, it was all good.


A bit of clean up, primer and paint, and I have it all done.


I am really pleased with how it all turned out. I have already benefitted from this as it let me trial fit hte head and barrels so I could play with exhaust mounting. A bit of copper grease was put on the threaded bar to help prevent any future corrosion. The bar is stainless, but the bungs are not, so this seemed like a sensible thing to do.

So the project rolls gently on!

Thanks again to all the folk who offered help and advice before I started this daunting task...and thjanks again to Archmill for his massive help. If you are thinking about doing this kind of CB surgery, you could do a lot worse than one of his kits. Just not on a sandcast though Mines an F2, so not quite so precious!

I am seriously contemplating doing this mod inn order to make working on the CB750 project a little easier, and to facilitate building the motor in situ, as well as potentially having to go back in to work on areas like the cam carriers...which I will have to fit less 'shiny' ones than I would like to begin with.

I have been frankly struggling with the project, not from the desire to get it done, but rather from a string of health issues, and arthritis. Displaced meniscus....ligament issues, and I am now potentillay looking at surgery to try and resolve this stuff.

So, I want to consider the options.

Carpys do a kit ...$139 plus postage, VAT etc.
Gordon's Mod .... $189 plus ransom demands and postage. Website is a little hard to navigate, so would probably need to e-mail to resolve.

Are there any options I missed?

Is there ANY supplier in the UK ?

I have a welder to install, as my little MIG set probably isn;t up to the job. So I would just tack the bits in place, then get a better welder than me to do the final job.

https://www.ebay.co.uk/itm/275817767179

Idly mooching through E-Bay on my lunch break, looking for those bits I just can;t seem to find, and got distracted looking at whats cheap and I ran across this....
did a double take .... spent the rest of my lunch wondering WHY!

Just been getting my various engine casings etc. painted while the unseasonable warm weather continues.

Had to lever out the rubbers that sit between the fins on my 750F2, which are hard as bullets and not particularly nice. The fins seem to have been drilled to locate these round bungs that spread into the hole to help them stay put.

Are they available? ( I can;t seem to find any, but may not be searching with the right terms.... )
Are they actually doing anything? ( they did cut down ringing vibrations on 2 strokes I have owned, but they seem to have deeper and thinner fins )

I knew from day 1 that I didn;t want a stock exhaust on my 750 F2 project. It's one thing that I have hardly ever had on bikes that I was riding back in the day, or was that fussed about. Original pipes rotted out, and when that happened the price of new replacements was always far beyond my pocket. So on would go the dodgy 4-1 if I felt flush....or something dodgy and cheap from a breakers if I wasn't.

Now....my bike came with a reasonable front half exhaust, bit rusty, but nothing too serious. There was some rot at the join which I have fixed, but the damn things refuse to come apart so I can finish the job. But even then, its gonna be a hell of a clean up job, and probably a rechrome to make them look presentable. If I can find somewhere willing to do the job on well used pipes.

I have looked to the second hand market. Dear god....do people really pay £400 and up for rusty and battered old exhausts? Everyone wants that for them, but I followed a couple on E-Bay and they don;t sell. Not surprised. The sellers don't seem willing to take low offers either, which is all I would pay for what looks like scrap to me.

I looked for new...and options are limited to 4-1 pipes I don;t really like, or some very overpriced stuff, mostly from the US. Earlier bikes have a flourishing ( and eye watering ) replica market.

But....there seem to be some options available for the DOHC early 4 pots. 79-82. A 4-2 with a pair of shorty mufflers would suit my build just right. But I don't know if they fit, have no way of checking, and really want to avoid having to buy something to find out its wrong. They head/exhaust ports look similar, and the only major issue I can see would be the sump would be different. The pipes may hang a bit low, as they would need clearance for the DOHC deeper sump. But I don;t know if that would cause problems in the corners...or not. I'm hoping someone out there has done it...and can tell me if it is worth the effort.

Meanwhile...I can carry on trying to find a full set of split collars for my exhaust. I have...1 ....where I need 8!

Does anyone know where I could get one made?

I am fitting rearsets on my 750F2 project, and the upper rear engine mounting bolt goes through the F2's chunky alloy footrest hangars and through the footrests themselves. The thing is 12mm diameter,  430mm long, with an M12 x1.25 thread at both ends. Well....as I dont have the footrests on this anymore, my bolt is about 30mm longer than it needs to be, and sticks out quite a bit on both sides. Plus, as there is about 20mm of thread each end, I would need to pop in spacers to tighten it up too. Just looks wrong.

I need to have one 30mm shorter.

At a push, I guess I could buy a spare stock bolt and cut it down...but I would also need to buy the right die to cut the thread, as all mine are metric standard...not metric fine. The bolt is also going to be fairly hard steel...so a decent die would be needed to cut hte thread I need before I chop the bolt down. I am not going to damage ANY of hte original parts that are usable, so the bike can be put back to stock ( or as near as it was when I got it ) at any time.

I am reckoning it may be cheaper to just get one made up

As I am looking for a few bits and pieces, I have been keeping an eye, specifically, on 750 F2 parts prices.

Have to say...some of it is absolutely shocking.

Under the seat is a plastic toolbox compartment....DK Spares were selling the bottom half ( minus top) for £49 ...and £25 for the top! A set of exhaust headers, with a socking great hole in one part of the collector with a crack on top....£45  The thing is basically scrap, with heavy rust all over.....£45. £250 for one with a massive patch over the silencer where it's blown out ( where they all go....I have one that did the same.... ) a big dent and other holes. Plus no mounting bracket. They wer eselling a sealed beam headlamp assembly for £60 as non working...the main beam filament has blown. £40 for one footrest.

Now I don;t know if these prices are ever actually obtained, but if they are....my discarded parts pile is worth around £500 in DK prices.  Rear grab rail, seat cowl, footrests, pillion pegs, footrest hangars, toolbox, rear light, rear light bracket, inner mudguard ( plastic), seat trim ....and some very rusty indicators.

This might be genuinely what these things are worth now, but it just seems to be getting a bit 'tasty' in terms of what people think rusty old motorcycle parts are worth. Especially parts that really don't look to me like they are ever going to be useable. Sure, a slightly scabby exhaust can be rechromed....but a pipe that has blown apart and rotted....you can't weld it. You can't rechrome it...its had it

I have had various bikes over the years with stock hoses and with braided steel...another back in the day 'fast lad' upgrade.

I have found some bikes responded well with braided hoses, and others felt wooden as hell and rather horrid. The things usually improved braking ..but a lot of that was down to the fact that they were replacing 15 year old hoses that were past their best.

So, what would be best for a 750F2 ?

My hoses are well shot, and the bike came with US spec high bars, so the front top hose was too long anyway. Rear hose was full of crystalised fluid and corrosion.....and was bin fodder too.
For the sake of safety, I want a full set of new hoses. No point in replacing seals and pistons etc. and NOT doing the hoses.