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APE 836CC Wiseco Kit for 1978 CB750 F

gatorforge

CB750 Enthusiast
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I've managed to luck into a 1973 CB750 for all of the bolts and screws I was missing on my 1978 CB750F so my build is finally progressing and I'm beginning to make some headway. I've lined out most of the parts I will need to order, however, I wanted to make some serious performance upgrades to the engine on the 78. When I received the engine, it was already pulled apart and i have all the components to rebuild it stock, however, I like the idea of the 836CC kit. I've been doing some reading on it, however, I can't seem to figure out how much needs to be shaved off the cylinders, and whether or not it will fit on the 78 at all. I see listings for the 69-77 and 79-82, but I'm not sure about the 78. Any help would be appreciated.
 
with the F motor you will need to get F specific pistons or you will have low compression. The F2 style head has larger chamber then the K heads. Cycle X and Dynoman both have F specific piston kits. It gets more involved trying to make K pistons work with a F head. You have to machine off a lot of the head to get close to advertised compression. If you have k series pistons then build the K motor and forget about the F. Let me know more of what parts you have already and I can advise you more on what you need to do.
 
Even more now..............the shop you have do the work will make you or break you. Local shops all say they can do it then give you back junk. Consider mailing parts across the country, the only way to be sure. Unless you are one of the lucky ones to have a dead solid shop right down the street of course.
 
@dirtdigger, I actually have two complete engines a 1978 F which is disassembled but in good condition, and a 1973 K which I haven't taken apart yet, as it is still in the frame on the parts bike, according to the junkyard where I bought the parts bike it urns over, but I haven't confirmed that yet. The bike that is in better shape and that I'm planning on building up is the 1978 F2 (it is also the only one of the two with a title).

@amc49, well I'm the one doing the work (with the exception of boring the cylinders) so...
 
If you are building the F2 motor then you need to get the F2 pistons. Did you buy pistons yet or still in the planning stage?
 
I meant the boring specifically, sorry. We know you can do the work, it's what you have to job out that commonly gets messed up. Boring is fast becoming a lost art.
 
@dirtdigger This is all still in the planning stages, parts aren't cheap, so I want to know what I'm buying, or need to buy, before I put the money on it.

@amc49 yeah thats the one part I haven't got figured out yet, and have no intention of attempting myself. cyclex has a program where they will bore the cylinders and port and polish the heads I believe. Are they any good?
 
Yes Cycle X does good machine work, have used them many times. Also have used APE for machine work as well. They also do porting on the sohc motor. I would call each of them as far as how long it will take. Cycle X gets backed up on there machine work so you may have to wait longer but I would suggest get a hold of each of them. Prices are just about the same between them.

In all honesty if you go with the F2 based motor you wont have to do any porting, maybe a smooth of the casting, they flow more then a small bore motor needs, but you will have to have it rebuilt at a minimum and use the upgraded parts...new guides, valves and upgraded aftermarket spring retainers. The K head really needs a good port job as they are pretty poor even with just a small 836. It all depends on if you want an actual F2 motor in the matching bike. If you dont care then I would go with the K motor, it will be dead reliable. Go with a little bigger cam but dont go too big or you will only have usefull power at a higher rpm. Any question on suggested parts just let me know.

If you decide to put the K in you will have to check drive chain alignment and probably change the rear sprocket carrier which is a simple swap. The sprocket on the F motor sticks out farther then the K.
 
I think I'm going to stick with the F2 motor in the bike and get the Wiseco 836cc piston. If I do though, will the factory connecting rods stand up to the stress, or at that point would I be better served going to Carillo rods or the like? From what I can tell so far, the factory rods currently in the engine have no defects or issues, but I haven't checked the bearings on the crank or the crank itself as the motor is not that far apart yet. I do plan on using the beehive full upgrade kit from Cycle X.
 
If you are just going to be street riding with the occasional run to redline then stock rods will be fine. If you plan on really thrashing the motor then at least look at the Cycle X Super Rods...they are cheaper then Carrillo rods but much stronger then the stock rods. I use them in a 970 street motor and they are good to go. Carrillos are realy only necessary for racing but they are great insurance if you have the money. Get new primary chains and heavy duty cam chain, and get new timing chain tensioner rollers if they are hard.
 
Thanks Dirtdigger. I'm going to start inspection get motor next week, so we will see how everything looks then. I'll definitely pick up the new chains though.
 
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