1979 CB750 DOHC Monoshock Build

[bananas]

One thing I did when making my seat pan and electrical tray was on top of the masking tape I used aluminum tape(for duct work, not duct tape tho) and waxed it and my parts came off easy. I was worried about the resin soaking into the masking tape and being a pain to get off. And I had saw someone else do that. And I'm sure the acetone is your problem I used same resin and parts came out fine and fully cured in less than a day, were hard enough to remove in hour or so, maybe less I didn't try earlier. Just my 2 cents worth, I am by no means a fiberglass expert but I did get useable parts with minimal effort.

Yeah my battery tray came out fine, a few air bubbles but otherwise will be perfect with a bit of sanding, bondo and paint. Although I did buy aluminum tape I didn't end up using it -- carnauba car wax worked extremely well and I already had some on hand. .

Styrene is the only thing that should be used to thin polyester.

Interesting. Forgive my ignorance as I don't know much about this stuff but would I just add a couple of packing peanuts to the mix?

 

[jpmobius]

The unhappy truth about working with composites is that in the main, they are extremely picky about what they combine with. Only the chosen few are friends, everything else is an enemy! The problem is, it is hard without some exposure to learn what is friendly, and maybe more importantly what is not. If you are learning, it is not a bad idea to go with all the recommended materials from a single manufacturer (like West Systems if you are using epoxy for instance) so you don't have to guess and chance ruining your project. Your packing peanut is likely expanded PVC. Pretty much NOT styrene, and very likely to have very much not the effect you are after! Using all the "official" chemicals from a single supplier helps a lot to avoid big problems. Some materials are very pricey, but worse, mixing the wrong chemicals together can make an incredibly dreadful mess and waste huge amounts of time!

FWIW, fiberglass, most commonly combined with either polyester resin or epoxy, is not like many other more familiar materials. All the chemicals used with polyester resin are in general completely incompatible with epoxies. We are used to using mineral spirits or turpentine to clean oil based paint, and using these to thin the paint is common. We also clean up our fiberglass work with acetone, but you can't mix polyester or epoxy with acetone without ruining the mix. And most epoxies are very sensitive to precise ratios or they perform badly. Polyester not as much, but still plenty picky for good performance!

 

[J-Rod10]

This is what you want. They may sell it at Lowes, Home Depot, etc. I've never looked for it anywhere else, though.

http://www.fibreglast.com/product/Styrene_Thinner_70/Resin_Additives

 

[bananas]

Hey everyone. Your old pal bananas has been very busy with other projects however things will get started again soon. Have begun building the wire harness and will update when it's ready.

To those asking about the M-unit, I found an awesome video on youtube showing one being setup. Mods please let me know if this is not OK to post.

https://www.youtube.com/watch?v=HNF-h6oBczg

Also, here's a picture of the somewhat incomplete wiring drawing I'll be using. I left out quite a bit of the Motogadget connections as they are super straightforward. The wires are coloured exactly as the stock CB750 setup. I'll update the drawing for my build binder once everything actually gets wired up.

 

[bananas]

So, obviously everyone's old friend bananas has been procrastinating on this build. I've recently met a dude that can do custom pull-through turbo setups for vintage bikes. Ever since I saw Guy Martin's GSXR hillclimber build I've been wanting one. This whole thing has me foaming at the mouth. I've been looking around for other people with turbo set-ups but there doesn't seem to be very many around.

Anyone know of a few good reference threads for custom turboing on a DOHC? I just want to get a handle of what's about to happen before I jump in head first.

 

[bananas]

So for anyone else pondering a vintage turbo setup, I've been looking into the upgrades I will eventually need for a reliable turbo setup.

Most of the dudes out there with turbo'd CB750s are more into drag racing than I am but from what I'm reading, depending on boost, I should be expecting somewhere about 100 WHP and doing about low 10's to high 9's in the 1/4. Cool.

There are some guys that do run stock motors but it is definitely not advised for higher boost setups. I'm thinking I'll run something like 6-8psi initially (or whatever the builder recommends) until I get the internals set up properly.

The standard mods required for a more reliable big boost setup are:

1. Balanced Crank
2. Aftermarket Steel Rods. Either Yoshimura or Carrillo. Big $$
3. Aftermarket pistons -- 8.5:1 or lower. Big bore recommended. Probably will go with the Dynoman Stage 1 kit.
4. Aftermarket valve springs / titanium retainers (For higher boost)
5. Heavy duty case/cylinder studs
6. Dyno tune

Alternatively it may be possible to run a combination 900F top end with 1100F rods but I'll need to do more research in the setup.

A few recommended but not required mods:

1. Boost/AFR/Oil Temp Gauges
2. Modern ignition
3. Clutch upgrade

I don't know what the hell I'm going to end up doing with the thing but hopefully she'll be reliable enough for the standard posing at Starbucks, cruising around the city and some high-paced long distance canyon runs.

 

[SilkySmooth750]

So for anyone else pondering a vintage turbo setup, I've been looking into the upgrades I will eventually need for a reliable turbo setup.

Most of the dudes out there with turbo'd CB750s are more into drag racing than I am but from what I'm reading, depending on boost, I should be expecting somewhere about 100 WHP and doing about low 10's to high 9's in the 1/4. Cool.

There are some guys that do run stock motors but it is definitely not advised for higher boost setups. I'm thinking I'll run something like 6-8psi initially (or whatever the builder recommends) until I get the internals set up properly.

The standard mods required for a more reliable big boost setup are:

1. Balanced Crank
2. Aftermarket Steel Rods. Either Yoshimura or Carrillo. Big $$
3. Aftermarket pistons -- 8.5:1 or lower. Big bore recommended. Probably will go with the Dynoman Stage 1 kit.
4. Aftermarket valve springs / titanium retainers (For higher boost)
5. Heavy duty case/cylinder studs
6. Dyno tune

Alternatively it may be possible to run a combination 900F top end with 1100F rods but I'll need to do more research in the setup.

A few recommended but not required mods:

1. Boost/AFR/Oil Temp Gauges
2. Modern ignition
3. Clutch upgrade

I don't know what the hell I'm going to end up doing with the thing but hopefully she'll be reliable enough for the standard posing at Starbucks, cruising around the city and some high-paced long distance canyon runs.

All that sounds very expensive for an old motorcycle.

 

[bananas]

All that sounds very expensive for an old motorcycle.

Yes, if you choose to see a bike built with love as just an 'old motorcycle'. The way I see it, even if I put another ten grand into the thing (not that I have the money) it'll still be a huge bargain in terms of smiles per dollar. You can't put a price on hillarity. Well.. maybe if you're into yachting or watches or something like that...

 

[bananas]

Had a friend come by to look over my wiring diagram and figure out how to install my new bar control setup. Everything looks great and I will finish up the wiring job once the new ignition arrives.

Since the thing is a custom I've decided to reduce my bar controls as much as possible. I really don't need all the standard motorcycle controls. I'm going to be running a "Creative Factory Posh" mini switch for my lights/signals and nothing else. The M-Unit allows the use of a single push button for hi/lo beams which is pretty cool so the Posh setup is perfect. Will be purchasing a marine automotive style ignition switch that will be hidden under the tank so I can delete the Start/Kill switches on the right side.

So the first thing was to take apart the mini-switch and create a drill template with AutoCAD. (If anyone wants this I can send over the diagram). The Posh switch requires three holes -- 19mm, 3.3mm and 9mm. I did the math beforehand to make sure it would fit into my Renthal Ultralow bars. It clears with an extra 4.75mm to spare for the wiring loom.

Nice and clean! Although now my grips look kind of stupid.

The switch housing itself is curved to fit perfectly flush with the bars. Just taped on for the photo. A buddy of mine will be helping me tap the hole.

 

[DohcBikes]

Hope your bar end doesn't break off now that it's super weak.

If you want 100+hp out of a vintage air cooled 4 get a Kawasaki or Suzuki so the bottom end lasts. Don't need a turbo to make 100hp, its just a waste. Like most turbo wannabes, probably just talkin' anyway. If you manage to get one put together that performs well i'll be the first to eat my hat.

 

[bananas]

Hope your bar end doesn't break off now that it's super weak.

If you want 100+hp out of a vintage air cooled 4 get a Kawasaki or Suzuki so the bottom end lasts. Don't need a turbo to make 100hp, its just a waste. Like most turbo wannabes, probably just talkin' anyway. If you manage to get one put together that performs well i'll be the first to eat my hat.

I'm more entertaining the notion than anything. The friend of mine that builds these things has a 400~whp GSXR. I trust his skills in the area. If I do end up with the turbo setup I'll be sure to let you know first. I'll expect a video of the said hat eating ;D

In regards to the bar -- totally weaker than before but these Renthals are beefy as hell. If the bike goes down I'll have a lot more to worry about than a $60 handlebar. In all other cases the bar will function fine.

 

[DohcBikes]

I'm more entertaining the notion than anything. The friend of mine that builds these things has a 400~whp GSXR. I trust his skills in the area. If I do end up with the turbo setup I'll be sure to let you know first. I'll expect a video of the said hat eating ;D

In regards to the bar -- totally weaker than before but these Renthals are beefy as hell. If the bike goes down I'll have a lot more to worry about than a $60 handlebar. In all other cases the bar will function fine.

A turbo setup that performs well. Make a note.

You wheelie that bike? I hope not because its gonna snap that bar right off and send your face into the triple before you crash.

I like the bike. Thanks for not having a fit over a simple comment or two.

 

[bananas]

A turbo setup that performs well. Make a note.

You wheelie that bike? I hope not because its gonna snap that bar right off and send your face into the triple before you crash.

I like the bike. Thanks for not having a fit over a simple comment or two.

Ah shit I do love wheelies. Any method of reinforcement that might work? Perhaps I could create some sort of external brace...

No I love the criticism. The way I'm built I can't be offended. Just not possible. For the turbo setup I could eat ramen for a couple of months and splurge on titanium rods and a beefy crank... might be worth it just to watch you eat that hat, hahaha.

 

[xb33bsa]

why dat hole so big? the thing about heat treated aluminum is that it will not give much warning it will just up and snap .inside the hole sharp gouges or grooves, in the direction of a break,will help the stress concentration for a fracture to happen, so polish up the hole a bit
that switch for a 7/8 bar or is it for a harley bar ?
you can getaway without weakening very much if a hole is limited in size... butt that gaper has ruined the continuity
i would say it is less than half as strong as original, that is it will flex easier and the flexing with the hole is too localized
if you must have that switch ,go to a steel handlebar is my best suggestion

 

[bananas]

why dat hole so big? the thing about heat treated aluminum is that it will not give much warning it will just up and snap .inside the hole sharp gouges or grooves, in the direction of a break,will help the stress concentration for a fracture to happen, so polish up the hole a bit
that switch for a 7/8 bar or is it for a harley bar ?
you can getaway without weakening very much if a hole is limited in size... butt that gaper has ruined the continuity
i would say it is less than half as strong as original, that is it will flex easier and the flexing with the hole is too localized
if you must have that switch ,go to a steel handlebar is my best suggestion

Shit I feel like I didn't really think this one through. The Renthal's curves and finish are just so pretty! Will polish up the holes ASAP. The switch is for a 7/8" or a 1", although I've never seen these installed on Renthals, mostly steel bars on choppers. I'm thinking I could build some sort of very clean wrap around external brace -- with a bit of jb weld and something kind of strong? Does that even make sense? Or I could start practicing landing wheelies holding the middle brace . Worst case scenario I'll swap these for some steel bars.

 

[DohcBikes]

It's just a set of bars.

They are ruined. The hole you drilled is too big.

Lots of bike there, don't fret over a lesson.

 

[bananas]

Lol damn, I'll figure out what to do with the bars later. I've read that cleaning up the hole to become a perfect circle + chamfering the edges will reduce the chance of stress fractures. The bike is still a long way away from running.

The larger 19mm hole is there to accommodate the three way toggle switch.

 

[jpmobius]

Usually I am on the other side of this conversation, but I doubt you will have any problems with the bars. That is indeed a mighty big hole, looks like it would have been better to make a slot with a die grinder - next time maybe. Great idea to smooth it out though. Street bike bars generally have a pretty easy life - stay off the moto X track and maybe a good idea to soft land those wheelies. Failure is very unlikely to be instantaneous, but if it does get a fatigue crack and you don't pay attention and notice it, it might seem that way if it does indeed start cracking - depends tremendously on the heat treating. Carefully cleaning up those holes will help a lot in preventing it. Try bending it now by hand - use enough force that you feel is within the range of likely use. If you can not damage it I'd run it and keep an eye on it. Do the bend test every so often. If it does start to crack you'll likely notice before it falls off in your hand. And if you are riding one day and you notice that grip starts vibrating differently - wake up!

Going to stay tuned for the turbo/hat challenge (dohc has a sense of humor after all!)

 

[irk miller]

How wide is that switch? Most clutch perches are 1 - 1.25" from the end of the grip. Weakness of the bar aside, I wonder if you have too far a spread for the lever. You might need finger extensions. I thought about getting one of these switches too, and always wondered how big the switch body is. It's a shame how big it is. I also hope there's room for your connectors. Doesn't look like it from my seat.

 

[xb33bsa]

How wide is that switch? Most clutch perches are 1 - 1.25" from the end of the grip. Weakness of the bar aside, I wonder if you have too far a spread for the lever. You might need finger extensions. I thought about getting one of these switches too, and always wondered how big the switch body is. It's a shame how big it is. I also hope there's room for your connectors. Doesn't look like it from my seat.

that blue switch housing plastic could have been trimmed down quite a bit as well, corners rounded and and overall cut back without ruining it ..plenty of meat there to gain the use of a smaller barhole,thats the way ide doit
like mjoboius was promoting it is not likely to break street riding ..;.but the alloy and treatment, makes them bars not like localized bending ,they do fine flexing a bit as a long spring, but the hole takes that longness away and any load will concentrate the flex in one really short zone,the one thing to avoid and also why the riser clamps should be radiused as well