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Hello guys, I'm new to this

Artless

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First off, hello to all you CB750 gurus and wrenchers, glad to join the conversation over here on these beautiful bikes. I also appreciate in advance any and all help and advice, and hope I can help others moving forward, too.

I bought a 1980 Cb750F as my first motorcycle, quite honestly with the intention of it being the first of many bikes me and my friend could buy, fix up and flip. As I bought the bike I started learning more and more about it and have fallen in love with it, choosing now to build it and hang on to it, well, pretty much forever.

That being said, I have found a lot of useful information online that has gotten me completely through the disassembly and ready to start putting it back together. At this point I do have a few questions as I am getting into more specific details with trying to make sure i get in tuned and running properly.

Here's a picture of the bike when I got it:
image.jpg

Here's the history to give you as much information as possible about the bike:
The bike was bought off of a 27 year old who seemed to have the bike because it was "cool". He claimed it was running good before the winter and didn't know why it was backfiring this summer. Upon finding the coils were wired to cylinders 1&3 and 2&4, I don't think he really respected the bike to learn to properly maintain it, and after he put many miles on it, it was more than he could handle to tune and repair. The bike has 20,000 miles on it with the stock carburetors running the stock airbox and 68/108 jets, as well as a 4-into-1 exhaust (that was poorly installed and leaking considerably). When I got it, after rewiring the coils 1&4 and 2&3, cylinder 1 exhaust was pretty cold (it's carb looking suspiciously dirtier than the others) 2 was warm and would get hot(ish) after warming up, and 3 & 4 seemed to be hot. Since I didn't know the extent of the neglect, and because the engine was very dirty and there looked to be excessive oil on the case around oil pump and chain area I decided to do a full rebuild.
 
What I've done/am doing:
I decided to replace all gaskets in the engine and all oil seals, as well as fully rebuilding the carbs. I purchased a small ultrasonic cleaner for the carbs and broke them down and am about to reassemble them. For the engine, I decided since I did all the work of splitting and cleaning the cases, I might as well bore it and not have to worry about the pistons not sealing or losing compression any time soon.

So, for the bottom end:
I elected to go with the Dynoman 835cc kit. I was able to find a new off-the-shelf OEM primary chain to install, but could not find the tensioners and guides anywhere. I do believe mine to be in good shape and will have to settle to reuse them. I cannot find a NOS OEM cam chains so I will be buying them from www.partsnmore.com later this afternoon. I did get a full gasket set for the engine I will be using.

For the top end:
I will not be touching the valves, and I will be reusing the stock cams with the 835cc bore, as well as the stock cam chain tensioners. My logic is that the parts all seem to be in good working condition, and things such as the chain tensioners are in abudant supply online so I can replace them if and when needed without having to split the case again. Ultimately I will be upgrading the cams and valves as well, but I don not have enough funds, so that will likely be a winter project (I also really want to get it running in the next few weeks and not miss out on the rest of the summer!).

Other misc. work:
I am replacing almost all of the wiring as a lot of it is in bad shape and I want to elimnate that as an issue. I will have the exhaust properly welded and have new gaskets to make sure it is sealed this time. I also am going to resurface the brake calipers (assuming they have enough width left) and new brake pads. I also got a replacement airbox filter and oil filter as well, of course, and will get new spark plugs.



My immediate question is, knowing that all bikes are different, what would be a good range of jets to buy and experiment with given that I will be running an 835cc bore with a 4-into-1 exhaust? More importantly, I would like to know all of your opinions and if there is anything critical I may have over looked or be aware of? Your help truly means a lot to me as I want to do this right and take a lot of pride in this beautiful new machine.



Note: I have no mechanic training and only know what I've researched myself on motorcycles, though I would say I'm mechanically inclined. I do have a talented welder friend who is trained as a mechanic and works on old English bikes, and through him I have access to the top BSA bike builder in Ohio who works out of his home in my city. I will be asking for their help on assmbling and things like mounting the new pistons to the rods.
 
What I've done/am doing:
I decided to replace all gaskets in the engine and all oil seals, as well as fully rebuilding the carbs. I purchased a small ultrasonic cleaner for the carbs and broke them down and am about to reassemble them. For the engine, I decided since I did all the work of splitting and cleaning the cases, I might as well bore it and not have to worry about the pistons not sealing or losing compression any time soon.

So, for the bottom end:
I elected to go with the Dynoman 835cc kit. I was able to find a new off-the-shelf OEM primary chain to install, but could not find the tensioners and guides anywhere. I do believe mine to be in good shape and will have to settle to reuse them. I cannot find a NOS OEM cam chains so I will be buying them from www.partsnmore.com later this afternoon. I did get a full gasket set for the engine I will be using.

For the top end:
I will not be touching the valves, and I will be reusing the stock cams with the 835cc bore, as well as the stock cam chain tensioners. My logic is that the parts all seem to be in good working condition, and things such as the chain tensioners are in abudant supply online so I can replace them if and when needed without having to split the case again. Ultimately I will be upgrading the cams and valves as well, but I don not have enough funds, so that will likely be a winter project (I also really want to get it running in the next few weeks and not miss out on the rest of the summer!).

Other misc. work:
I am replacing almost all of the wiring as a lot of it is in bad shape and I want to elimnate that as an issue. I will have the exhaust properly welded and have new gaskets to make sure it is sealed this time. I also am going to resurface the brake calipers (assuming they have enough width left) and new brake pads. I also got a replacement airbox filter and oil filter as well, of course, and will get new spark plugs.



My immediate question is, knowing that all bikes are different, what would be a good range of jets to buy and experiment with given that I will be running an 835cc bore with a 4-into-1 exhaust? More importantly, I would like to know all of your opinions and if there is anything critical I may have over looked or be aware of? Your help truly means a lot to me as I want to do this right and take a lot of pride in this beautiful new machine.



Note: I have no mechanic training and only know what I've researched myself on motorcycles, though I would say I'm mechanically inclined. I do have a talented welder friend who is trained as a mechanic and works on old English bikes, and through him I have access to the top BSA bike builder in Ohio who works out of his home in my city. I will be asking for their help on assmbling and things like mounting the new pistons to the rods.

Man I am excited to see what comes of this! Nice to see a fellow Ohioan as well! Doing basically everything I would like to eventually do with my '82 750SC. :thumbsup:
 
The stock carbs will be a nightmare to tune with the mods you are doing. They are a pain to get to run right with a stock motor let alone what you are doing. You will need to look into getting some CR carbs if you want to get it running well. Inspect your cam chain tensioners closely because they are a failure prone part..especially the chain guides.
 
Great post - I am building an 81 F after having it in storage for about 15 years, I want to put the wiseco 835 kit and if I can spare the $$ a little cam work. Still kicks over n runs - needs both cam chains replaced and has an electrical issue, after new battery, regulator, stator etc and Hours of trying to track it with that mysterious thing called a multi-meter I have decided to replace thee whole loom (never did one before) I have the full original workshop manual that has a coloured wiring diagram and a big arse board and wiring pins to lay it out on, but any tips or things to watch out for would be greatly appreciated
 
I finally got my heads back from the shop and am getting ready to reassemble this weekend if I find time off of the restaurant.

any tips or things to watch out for would be greatly appreciated

AussieCBNut, I would say if there is anything I regret it is not taking enough photos of hows things were put together. I would usually take a few photos, take something apart, and then not want to take my greasy gloves off for more photos. I have an iPad in a gallon zip lock bag that I use to look at photos in the garage. Buy the Clymer's Service Manual. Better than the Haynes from what I've heard, and it has enough pictures to get you through almost everything.

Obviously a carburetor rebuild would be wise, as it can be a huge trouble area. THIS WAS A LIFE SAVERr:http://www.cb750c.com/publicdocs/SeanG/Honda_Carb_Manual_revG.pdf
Which is linked from here with more useful info: http://www.1stkickmoto.com/how-to-rebuild-your-cb-750-dohc-carbs/ I also recommend using a sonic cleaner, I got one fairly cheap from Harbor Freight that was big enough for the individual carb bodies, I just had to rotate and rerun since the full body will not submerge. I used Simple Green Extreme Aviation (the same as the purple Simple Green HD I believe) in a 2:1 water to S.G. ratio in the sonic cleaner and the carbs looked great after. DO NOT USE REGULAR SIMPLE GREEN, it will corrode aluminum. Extreme could still possibly remove paint and clear coat if concentrated enough and left on long enough. Maybe not as good as paying a professional with a sonic cleaner, but cheaper, and I was able to wash lots of small bolts and other miscellaneous parts. Carb cleaner was shooting out of all the ports, passages and opening with easy after a few cycles in that thing. Here's a before and after (getting them back together was Christmas in July, thus the beer):
IMG_2923.jpgimage11.jpg

As for wiring, I did just buy new harnesses, my wire was in terrible shape and it was just over $100 for the main harness, I am going to rewire the alternator stator because I can only find the whole assembly there, but vintagecb750.com has all the little connectors for cheap, and admittedly my dad runs an electrical contracting company that my brother is in the apprenticeship for, so I have some help in the electrical areas.

With bolts, I put everything back in it's hole as soon as I could to keep track, but when cleaning called for removal, I found it very easy to make little masking tape flags and number the bolts, then snap a quick photo.
IMG_2907.jpg


A few mistakes I made:
-Keep the rod and crank bearings (half circle metal piece that mates to case and surface where the rods connect to the crank) in order. I mixed up the ones in the case and will just be crossing my fingers now...
-For the older gaskets like the oil pan and such, don't waste your time or money on chemicals and scrapers, I was able to get my case and covers blasted with walnut for $60 after TONS of frustration and hours wasted. It seems safe on aluminum, but I would have him focus only on the areas with old gasket or the exterior if you want paint removed. I think he pitted the bearing surface slightly on mine, again fingers crossed here. Soda blasting could be done, but it does stay imbedded in the aluminum and if not removed properly, can cause issues with it alkaline properties as far as new paint and such. If you can find vapor blasting, that has had unbelievable results on my friend's bike, although he had to ship his and wait 4 months, not an option for me with no one local around.
-In general, stay over-organized. I would dissemble, hit a delay, have to wait on parts or work, and then go back to where I was working and have few bolts or such laying around that I couldn't remember where they belonged. And this is with me having a full, moving 8 shelf rack dedicated to organizing parts. It's those "oh I'll just set this here for the time being, obviously I know where it goes" that will get you when you have to take a week off building. Same with photos here, don't be lazy and go "oh I'll remember how this goes back on". Besides, then you can document a full project for someone like me who isn't a mechanic, just a very daring hobbyist. I wanted to create the ultimate resource for people, and was too hasty and anxious to work to stop and take photos.

If you PM me I can send you my email and try to help with what I've learned going through my experience.
 
With new carburetors out of my price range for now, I am still wondering if anyone has advice on jetting and such for the big bore I did. The primary jets are still the 68's, I'm guessing this might need to change? I bought off brand secondary jets, I know they may not flow the same as genuine Klein, but I got a kit significantly cheaper and would have had some guess work anyways with the mods I've made. I figured since it was running rich at with 108s on the previous owners set up (though I think this was due also to him wiring the spark plugs wrong, cylinders 1&3 and 2&4), I figure I would start with 110s, expecting this to run rich still with the big bore and then I can work my way down. I do have jets as big as 125s, should I start higher? And along with that, any advice on modifying the air-box so I can get the appropriate air flow increase to go with the increased fuel levels for the big bore (835 according to the DynoMan kit)?

I know there are no definite answers, just looking for guidance so I don't do something that can't be un-done. I know I won't get the best performance without new carbs, cams and a valve job, but I just want to get in some riding this summer, break in the rebuilt engine safely and avoid damaging the work and new parts that have gone into it. I will worry about getting tip-top performance and reliability this winter for next summer.
 
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Also, sorry to blast so much info and questions, I'm just very nervous about this engine going together properly, hate to do all this work and it blows up in my face.

Any advice as far as if I need assembly grease? Should i prime the oil pump with it or Vasoline, changing the oil after running it briefly to get all that out? Can I just submerge the internal parts all in 10w-40 oil as I am reassembling, and if so, how long could it safely sit before initial start up? Will turning the starter several times prime the engine and avoid possible damage before letting it start up? I will change the oil either way with cheap 10w-40 oil to flush the system twice before filling it with Rotella, which seems to make these bikes and their clutches very happy.

These questions are hard to find straight forward answers to online, what are all your thought?
 
Great feedback and links, thanks Atlas. I will be watching and following your build with keen interest. Expect a few questions (probably obvious ones, but hey we all have to ask em right?) thanks again.
 
All the bearing surfaces need assembly lube. You can dip the chains in motor oil. Prime the oil pump with engine oil. I normally change oil after 50 miles on a new motor and inspect the filter for large amounts of metal...you will see some in the first oil change but you shouldn't see much after that.
 
Thanks dirtdigger, exactly what I needed to know. I went to reassemble the engine this weekend and discovered that, quite unfortunately, my main bearing for the crank that go into the lower case were knocked around on my work bench. I cannot be 100% positive that they are in the original positions, and there are warnings everywhere that they need to go in the original locations. If I plastigage them and the clearances are good, can I just reuse them? I know they crush into position and I'm worried that I'll spin a bearing possibly after all this time and money. Even worse I may have cleaned some of the ink markings that would allow me to find the correct original bearing size. I'm going to look again now...

EDIT: I may have gotten lucky, in the day light I can make out some markings but it appears some are maybe gone. Here is what I've got:
image.jpg
image.jpg
image.jpg

So as the letters are oriented, with x=blank, the flat surfaces read:
B x B x B B x A <--top
2 x <--bottom

The crank case code IDs as stamped are: B B B B B

Is this all necessary info? Both the Clymers and Honda manuals pictures and instructions are just vague enough that I cant quite wrap my head around it. Most of the info online pertains to SOHCs and isn't helpful either (I actually cleaned my crank in an effort to find etchings :doh: )

I guess I've reached my threshold as a novice mechanic, I appreciate your guys' help pushing through it. Going to feel real proud riding this bike around when I finally get it running! :bike:
 
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as long as the bearings themselves are in good shape you can reuse them no problem. I reuse used bearings all the time. As you said just plastigage them to check clearances. you lucked out and all will be green bearings except the A code stamp and that will be a yellow, hopefully you will find two halves with yellow marks then the rest can go anywhere. This is assuming the clearances will check out, if the motor has a lot of miles the clearances will be getting pretty loose and you should do new bearings but I would sort them out and plastigage them. The same procedure is used with the sohc motors so it all crosses over.
 
Ultimately only two of the 10 main bearing for the crank have green, the rest I cannot tell. They are showing copper-colored wear, so I am going to replace them. I am now curious as to if I should be concerned about replacing the cap end bolts and nuts for the rods, is this a concern, especially given that I have bored the engine out to 835cc?
 
If you can find new rod bolts I would use them. Stock bolts are always the weak link in the bottom end. The rods normally hold its the bolts that let go.
 
Absolutely no luck on finding the bolts any where. My options as I see them now are just hope the bolts will hold or buy new rods that will include the hardware. Digger, do you or anyone else know if the con rod bolts from an older SOHC would work? That would mean I could possibly buy the CycleX bolts they make for their rods. I also don't know if Honda has a unique design on their con rod bolts, as ARP does manufacture a lot of bolts, including for the connecting rods. I could possibly match dimensions if anyone know what they are.

EDIT: At this point, unless the CycleX SOHC bolts are a direct replacement, I will likely just reuse my bolts until I can save some money and upgrade the rods. I am not going to be racing the bike at all, though there will be quite a bit of highway driving and I imagine I will get on the throttle occasionally like anybody that just spent months rebuilding a bike, does anybody think this plan is too risky given the big bore? Or should I be alright so long as I don't push the bike often?
 
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ARP would be the best bolts if they have them in that size, I have never checked but that would be a good place to start. If not then just reuse them, make sure to use an accurate torque wrench so you dont over torque/stretch them. If something doesn't feel right when torquing them then throw them out and look for a source for bolts. I would call Kenny at cyclex, he will tell you what fits and may have a source for bolts. You have to call them though because they are extremely busy and dont answer emails very fast.
 
So in talking to a manufacturer of aftermarket rods and other performance parts, he had this to say:

"You can never go wrong replacing the bolts when they are available, however the stock bolts can be re-torqued a few times without danger of them failing. Unless you have mega miles on your motor or some gorilla over-torqued your bolts in the past you should be OK. Rod bolts do not usually snap off, but stretch enough for the oil pressure to drop between the bearing and the crank. This can cause the bearing to contact the crank and fail. We see this in the older SOHC 750s occasionally, but not on the DOHC motors.

It is also a common mistake to install much stronger bolts that require more torque, however as good as this sounds it can cause the ID of the rod to distort and have to be re-sized. Just make sure that you have an inch pound torque wrench that is calibrated correctly and you should be fine. Also make sure that you run the best gas available in your area, as pre-ignition can cause rods to fail as well."
!This is fairly relieving, and I think that ultimately I will reassemble with the original parts, and then this winter, if I save enough money, I will replace the rods just for complete piece of mind the next 20,000 miles of this bike. Hope others find this helpful as well.
 
Quick question... A little off topic. I just got a 79 10th anniversary limited edition. There is a little bit of fuel that has been sitting in the bike for at least 2 years.I open the tank and look for fuel...I can smell it but I can't see it. I put a plastic rod inside to see of it has gelled up but I cannot even get the rod wet. So very little fuel. Will it hurt it to put maybe 1/4 Gallon in the tank and try to start it up? Or should I just keep it safe and clean the tank and carb?
 
Quick question... A little off topic. I just got a 79 10th anniversary limited edition. There is a little bit of fuel that has been sitting in the bike for at least 2 years.I open the tank and look for fuel...I can smell it but I can't see it. I put a plastic rod inside to see of it has gelled up but I cannot even get the rod wet. So very little fuel. Will it hurt it to put maybe 1/4 Gallon in the tank and try to start it up? Or should I just keep it safe and clean the tank and carb?

Gasoline left sitting apparently turns to something called "varnish", I guess it looks like varnish because it turns a yellow
color and dries to a hard coating. But it really stinks and not like gas anymore, you can tell by the odor if it has turned to varnish.
And yes unfortunately if the gas has turned to varnish a good cleaning will be needed, any gas left in the bowls clogs up all the jets
and passages in the carb. Any gas left in the tank will clog up the petcock. Cleaning the carbs and petcock is well worth the while if the
bike hasn't been started for any length of time. Have you taken the tank off and shaken it to see if anything sloshes around?
You may just be smelling fumes?

But if you just want to see if things are still working you can always put an inline filter after the tank before the carbs and see what collects
in it. An inline filter is worth doing anyway in case of rust and other particles that may end up in your carbs.

good luck with it.
 
Gasoline left sitting apparently turns to something called "varnish", I guess it looks like varnish because it turns a yellow
color and dries to a hard coating. But it really stinks and not like gas anymore, you can tell by the odor if it has turned to varnish.
And yes unfortunately if the gas has turned to varnish a good cleaning will be needed, any gas left in the bowls clogs up all the jets
and passages in the carb. Any gas left in the tank will clog up the petcock. Cleaning the carbs and petcock is well worth the while if the
bike hasn't been started for any length of time. Have you taken the tank off and shaken it to see if anything sloshes around?
You may just be smelling fumes?

But if you just want to see if things are still working you can always put an inline filter after the tank before the carbs and see what collects
in it. An inline filter is worth doing anyway in case of rust and other particles that may end up in your carbs.

good luck with it.
Thank you for the feedback. I have taken the tank off and removed the carb. I am going to get carb cleaner from AutoZone or something. I dont exactly know what to use to clean the tank.

Side note. I have very few tools. Zero specialized tools for the job. Zero experience and scarce finances. Haha.

Just going to disassemble the carb, clean it, clean the tank, order gaskets and screws (along with whatever else I need to replace), reassemble and hope it runs as smoothly as it did when I got it.
 
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