just bought 78 ss

[K2750tracy]

just picked up a 78 cb750F $500 not bad condition, the engine wont turn but I believe the kick starter shaft is froze not the engine. has funky 70's flames on tank and side covers. will start to go over it this weekend. Get it running then decide what direction to go.

 

[K2750tracy]

couple pics as it sits in PO' yard

 

[grepper]

Either way, these old bikes have been known to free up and run again.

About a year ago I bought a 74 parts bike that had sat in a guys yard for several years. It was really rusty and the engine was locked up. While trying to get the alternator stator off, I ending up freeing up the engine by accident... who knew.. It's actually acting like it's got good compression.

 

[K2750tracy]

yeah I had a cb550 that was frozen parted out all the tins and wheels. went to move the frame and motor pushed on the kicker and it spun over, the motor now sits in a nice café bike running strong

 

[K2750tracy]

Got 78 750F home today here are a few shots before I cleaned it up. could not get engine to spin with kick or starter so I pulled the plugs and put some Marvel mystery oil in cylinders #2 plug came out hard seems that one might be seized. will give it a day then try rocking it in gear. PO said he had it running last June so it cant be froze to bad. got a couple extras with it, an ugly vetter fairing, several brake calibers and a clymers manual, though I have the factory service manual. any body need a fairing with mount?

 

[K2750tracy]

pulled the carbs and exhaust off today and put Marvel oil in the exhaust and intake ports to help lube and free up the valves also. The exhaust ports all had a fair amount of white looking ash / corrosion in them pulled it out with a rag and the valve stems were very black and sooty underneath, hoping the soot and oil keep them from getting stuck. carbs are pleasantly not in bad shape , everything moves freely.
.

 

[K2750tracy]

Engine still stuck on this thing, guess i'll just keep MM oil in it and let her soak some more.

 

[K2750tracy]

Looks like i'm removing the engine and tearing it down. Have to see how bad it is then most likely go with a 836 kit and Cycle X cam to build it back up.

 

[dirtdigger]

There are some other things I would suggest to replace before you get it back together. Heavy duty cylinder studs are a must, if cases are split replace the timing chain, primary chains if over 20,000 miles. timing chain rollers are probably hard and brittle so new or cyclex timing chain tensioner upgrade. Also make 100% sure it is a F2 motor and has not been replaced with an earlier motor. You want to be sure to get the correct 836 piston kit. There are f2 specific pistons. If you put a K piston set in the F motor you will loose compression as the cylinder heads are different with a larger chamber. Look for a 410 on the cylinder top fin on the back by the intake in between cylinders 2 and 3. These cylinder heads are bad for wearing out the exhaust guides so you should check for guide wear as well as they have weak valve spring top retainers. You should replace the valve springs if going with a bigger cam anyway, and they are f2 specific. If you are looking at getting some good power out of the motor then there are some other things you should look at doing along with the cam and the pistons.

 

[K2750tracy]

Thanks Digger all good stuff to know. I will order most parts from Cycle X. Bike has 22,900 miles on it, engine is original and has 410 on it, i want all the power i can get out of it with out going any bigger than 836. I have a set of Cycle X super rods from a K motor will they work in the F2? I know you use APE for head porting is this something i should consider? What carbs would you recomend also? Thanks for all the info.

 

[dirtdigger]

yup the super rods will fit, bottom end is the same as the K. I am running the super rods and they are good quality. Not sure how much money you are wanting to spend on this build but having the crankshaft lightened and balanced makes for a smoother faster revving motor. Definately need to get an adjustable cam sprocket to dial in the new cam. The F2 already flow much better than the K heads and they come stock with larger intake and exhaust valves. If you want to make power you need to have the head worked on, that is where the 750 makes its power or lack of power if you run a stock head. At a minimum I would have guides and a valve job done provided the valves are in good shape...along with good valve springs. Ape and Cycle X both do porting on the 750's...I hope you have better luck getting through at Cycle X then I have the last couple of months, not sure what is going on but I cant get a response back from email and it took 4 calls to get an answer back. Still love there parts but I am losing faith in the customer service at the moment. But yes I do suggest having head porting done but be prepared to shuck out $800 or so for porting then the guides, valve job on top. Yes a good head costs some $$$ but as the saying goes...speed costs money how fast you wanna go??

i am in the same boat for the carbs. I really need to get some good aftermarket carbs for my 970 build. But will be going after a set of carbs like yours has stock. They are slightly bigger than the early ones. Money no object go for the Mikuni's cycle X is selling, very good carb. You could also have Cycle X bore and rework your stock carbs to get some more airflow, they do offer this.

I have some good pictures in my galleries of the motor internals I have and will be putting up more ones I start to get all my parts rounded up and bakc to me for my 970 build.

 

[K2750tracy]

Got the engine out and tore the head off nothing looked real bad, taped on #2 cylinder with soft face hammer and it broke free, cylinders arn't scored or pitted, looks like i could get away with a honing and fresh rings, but i really want to bore this engine to an 836 and cam it up. Have to get through Christmas then i can devote some cash to this project.

 

[K2750tracy]

Wondering if there is any difference in the engine of a '75' 750F and a '78' 750F

 

[dirtdigger]

yes, the head, cylinder, pistons, camshaft, cases, tranny gearing are all different.

 

[K2750tracy]

So the 75-F is a basic 69-76 k engine.

 

[dirtdigger]

Yes and no. The F does have different pistons, camshaft and different gearing in the transmission. The chambers are different in the heads also. But then there are several different chamber desings in the k motors too. The 75f head is more like the earlier k type heads. The 76f is more like the later k heads. But they are completely different from the F2 head. The 76 k and 76f started sharing some of the internal parts.

 

[K2750tracy]

Thanks Digger, im getting a 75 F that's been sitting on a covered porch for the last 31 years! every thing is frozen solid except the motor it turns over easy, (go figure). complete bike one owner 21,900 miles last inspection sticker is 1982 PO's widow says it hasn't moved since he parked there in 82 when he bought a new Harley. im sure it will need all the seals and plenty of work, but im hoping to get the motor running and put into the frame of the 78 F. Then I can build the F2 engine for my K2 Tracy body café. What I can salvaged from the rest of the bike will be up for sale.

 

[dreadstar]

hey there in P.A.! I have a ton of 78 f,andk motors parts etc.if ya need anything holla. DO YA STILL HAVE THE FAIRING?

 

[K2750tracy]

Yeah I still have it and the mount.