Topic: 1st timer getting my 75 cb750f back on the road.

[Lazerviking]

I purchased a 1975 cb750f a few months back for $1500, it had a rattle to it when it idled but it seemed to go away once it was in gear. I talked to a few buddies and it seemed like nothing we couldn't fix, so I crossed my fingers and took her home. This is my first bike and I have little experience working on vehicles but feel confident in my ability to figure things out, as well as have a handful of friends who are experienced in the art of making bikes happy. Here's my bike when I got it.

Here's the back after losing a little weight.

When I purchased it the fella I bought it from said he sometimes had trouble getting it into 5th gear which, upon opening the engine I can see why. The primary chain seemed the #1 culprit for the chatter I was experiencing and upon opening the oil pan and checking it I seemed to be on the right path. Once I opened the cases I was surprised to see a few of the gears on the transmission had the dogs chewed up bad.
pulling the engine...

top has been popped...

and cases cracked...

my dogs are dogged!

[Lazerviking]

I'm currently shopping for a replacement transmission. I kept going back and forth between completely restoring everything on my bike but have decided that my wallet will not allow for such a project. I guess one big thing I wanted to accomplish by posting about my rebuild is for any advice folks with years of experience have to throw my way. This forum has already been a tremendous help and I very much enjoy learning from everyone on here. Feel free to toss any advice my way, no matter how grade school it might be, I am basically starting from scratch and can use all the help I can get! 

My plan for the lower end currently is;
-Pull everything from the cases and clean them thoroughly(metal shards everywhere)
-Replace transmission
-Replace primary chain and tensioner
-Replace bearings as needed(still need to inspect the existing ones)
-Replace cam chain and tensioner

Let me know if I'm overlooking something rather important. I feel like I am.

[Jerry Rxman Griffin aka MuthaF'er]

Looks to be low mileage? I like the color. Is it a good paint job (not original)? What's your serial number? More of a 76 color.

Is the exhaust as nice as it appears?! Nice stock ones are impossible to find.

If those are original shocks you're going to need to replace them.

Unfortunately, HONDA has recently discontinued the primary chain tensioner!!

Tsubaki heavy duty cam chains can be had for less than a stock chain.

Maybe you won't have to replace much engine stuff. Chains are a good idea but may not be necessary. Depends. Main bearings from what I see look good. If it wasn't burning oil you can probably get by without rings too.   

If the clutch rattles there are a couple 'fixes' for that both of which can be done after you put it back together. PM me if you find that's the case and I can help with that but take care of your tranny and get it back together first.

If you plan on keeping it for a while and you do not want the infamous head leak they will all eventually get or at least want to put it off longer you may want to consider a MLS (multi-layed steel) head gasket CycleX) and heavy duty studs (APE). How tight were the head bolts/cylinder stud bolts when you cracked her open?

Aftermarket sidecovers are available here through Franken----- (whatever he's going by these days)

Sidecover emblems will be difficult to locate. One used one on EBay currently. Then there's always JTMarks on EBay but he is REALLY proud of his stuff and you'd better want it really bad $$.

Oh yeah, the seat. That just ain't gonna work! LOL. Corbin makes a really nice replacement. If you go that route do NOT cut up or discard the bottom trim. Impossible almost to find!

Feel free to PM me. 

[BeSeeingYou]

The 4th and 5th gears on the F have a different ratio than the K otherwise it's the same.  The F will run about 500rpm higher at highway speed.  If you wanted the bike for long distance highway travel the K tranny may be a better option.  A little more power around town the F might be better.
 
Your bike looks like it was in good shape except for the tranny...how many miles are on it?

If you don't plan on keeping the side bags let me know I would be interested in buying them.

[Lazerviking]

Hey Jerry,

It reads 28,000 on the odometer. The paint is not original but was done well, it says the 75's came in either sapphire blue or sunrise orange. The emblems were put on with adhesive or silicone that squished out the sides and looks crummy.

The exhaust is in excellent condition thankfully, and I'm not sure if the shocks are original or not. How would I tell if they are?

Whats the going price for a primary chin and tensioner these days? The ones I've seen are pretty pricy but I haven't seen them for less any where else. Hopefully that takes care of the rattle, but I will be pm-ing you if it continues.

Thanks for the advice on the Tsubaki heavy duty cam chain, its actually on my list! As well as the mls head gasket!

I'll be shopping around for side covers and emblems after the engine is happy, I'll make a note of Franken and have to bug him about some sweet side covers.

[Lazerviking]

The 4th and 5th gears on the F have a different ratio than the K otherwise it's the same.  The F will run about 500rpm higher at highway speed.  If you wanted the bike for long distance highway travel the K tranny may be a better option.  A little more power around town the F might be better.
 
Your bike looks like it was in good shape except for the tranny...how many miles are on it?

If you don't plan on keeping the side bags let me know I would be interested in buying them.

Thanks, I plan on doing some long distance rides with this bike so that's good to know! I think I'm going to hold on to the side bags for now but I'll let you know if I change my mind. They are in great shape except for one of the lids is missing

[Lazerviking]

I can't believe I didn't catch this until now but I just noticed that my frame number is cb750f-1006196 but the engine number says cb750e-2704381. Which if I'm not mistaken means the frame is 1975 but the engine is from 77f??? Am i crazy? The guy I bought it off of said he and a friend "rebuilt it" but didn't say anything about swapping the engine.

Crap. At least I haven't started buying parts yet...

Jerry do you know if a 76k transmission will work with a 77f engine?

[Jerry Rxman Griffin aka MuthaF'er]

I'm on the road working so I do not have any reference materials. GOOD catch on the numbers! The cases are the same so the 76 tranny would fit 77/78F's. Different gearing and output shaft as you know. Gearing can be affected most easily by the front sprocket so that's somewhat of a non-issue. Verify that engine number then count and compare the 4th and 5th gear teeth counts. May already be mixed and matched if 'the friend' has been playing already.

The 77/78 F engines have the larger valves. As has been mentioned in another post about head ID'ing the 75/76 F and the 77/78 K head has a 392 cast on the top fin intake side close to #3 and the 77/78 F has 410. That'd help ID it also. HOWEVER many people swap out whole top ends due to the notorious valve seal issue the 77/78 F has. SOOOO a 77/78 F COULD have a different top end cases up.   

Now somewhere along the way perhaps beginning with the 75 F there was a double row ball bearing used (on the output shaft maybe)? This needs to be checked on and overcome as PERHAPS the 76 K had the old single row. Let's get some experts weighing in on this too and with the possible fix/swap. Check the fiches on this.

This is all do-able. Just gotta take the time to learn and do it correctly. Just take notes for the next time it's cracked open.
 
Shocks LOOK original, They didn't last long. You'd know when they bottom out and wallow around   

Primary chains can probably still be had for under $100. When you order 1 you get 1 set of 2 so do NOT EBay them! Good luck on finding a tensioner now... I use ServiceHonda.com. ~30% off and the order I just placed initially said $30 shipping but they only charged $20. I can do more research on all these things on Monday at the earliest.     

[Lazerviking]

Okay sweet. I will do a thourough investigation on Saturday and report back on the findings. Thanks again!

[Lazerviking]

I have the transmission pulled out completely now. The only thing I was having an issue with removing was the shifter drum. I removed the end bolt with pins and plate but the drum won't come out. Do I need a puller for this or just elbow grease? I was worried if I tried to force it out I would damage something.

I got in contact with the fella who I bought the bike from and he did confirm he replaced the engine but had no idea which year/model it came from. Its looking like a 77k. I looked for the numbers you mentioned Jerry, but didn't find either of those. This is what was there...

[Jerry Rxman Griffin aka MuthaF'er]

As you get into it these are some things to look for to ID it as a 75/76 F or 77/78 K.

'392' pistons - notice the 392 casting



'392' combustion chamber - notice the smooth surface vs earlier heads with swirling inside the chamber which I do not have a picture of



'392' head ID castings. My 75 F marking is slightly different than the 78 K but they both have a '392' and the 78 is also hand stamped 'K8'



You shouldn't need much force to slide out the shifter drum. Without me doing one I can't say if there is a trick or not. I'm thinking that the neutral switch on the outside of the bottom case half may be your problem? Remove that and see what happens.

[Lazerviking]

My pistons all have the 392 on them but the head only has a X 7 and then off to the right another stamp that is hard to determine what it is. Maybe a K? Hard to tell. I can't tell if my combustion chamber is smooth or swirled?

[Jerry Rxman Griffin aka MuthaF'er]

Looks like a -392 engine to me. Pistons for sure. Head also. Don't see any swirling in the chamber, just smooth. Wish I had a pic of an earlier head for you to see. The serial number verifies what you show too. "Engine # CB750E-2700001 and subsequent" IS A 77 750K.

OK, where were we? We're getting somewhere now.

Oh yeah, tranny etc. A 76 K will work. I'm not sure but the 76 K tranny, etc may have a single row bearing on the output shaft and it's a 530 while the 77 K has a double row bearing and is a 630?? I'll attempt to cross reference some parts and report back.

What I can't say is that the output shaft of the 76 will work with the tranny of the 77. We need some guys to chime in here that have experience on this and how best to make it work. Teeth count good/same? Lots more questions. 

I'd say measure the chain and the sprockets to see what it has. 530 or 630. May be good to go already in that regard.

[Lazerviking]

Eureka!! Progress feels good.

As far as transmissions go, I have been in contact with a couple of folks about purchasing a transmission. One is a 76k and the other is a 77k. Hopefully the 77 works out for simplicities sake. Fingers crossed.

Here's a shot of the output shaft for determining a double row bearing or not. 17 teeth on the sprocket aaaaaaaand I'll get back to ya on the other teeth count.

I apparently do not know how to post pictures right side up...

[Cragdog]

Good Luck on your bike! Hope you get it back on the road soon!

[Lazerviking]

Its been soooo long since I've posted, but I'm making progress again after getting bogged down by school and life. So I'm in the process of putting the cases together right now. I've cleaned them and painted them, new bearings and replaced the transmission. Here goes putting those cases painted and back together...

[Lazerviking]

After I flipped the engined over and was tightening the bolts on the top case the first bolt I tightened snapped on me. Its a 6x100 flange bolt, one of the 4 in the center of the case. I'm sure everyone is going to tell me I have to open up the cases and replace but I'm curious what issues I would run into if I just left it. There are 3 other bolts tightened appropriately, am I really going to notice a difference?
Just curious, because I'd really prefer not having to open the cases after I finally just get them sealed shut. Here's a picture of the bolt I busted.

[SOHC4 Cafe Racer Fan]

Really?  Open it up or have a potential problem that requires more labor to correct it later.

[brandEn]

Really?  Open it up or have a potential problem that requires more labor to correct it later.

yup.
just think of how much easier it is to fix now.

[SOHC4 Cafe Racer Fan]

Really?  Open it up or have a potential problem that requires more labor to correct it later.

yup.
just think of how much easier it is to fix now.

I didn't mean to sound like a jerk. Branden expressed it better.

[Lazerviking]

Really?  Open it up or have a potential problem that requires more labor to correct it later.

yup.
just think of how much easier it is to fix now.

I didn't mean to sound like a jerk. Branden expressed it better.

Haha, yeah I know. I actually already purchased the replacement part. After my initial frustration at having to open the cases up again after finally closing them had worn off, I knew what I needed to do. It's just so irritating. Two steps forward, one step back.

Thank you guys keeping me in line.

[brandEn]

Good decision. Trust me I know how you feel. I have been there more than once. I'm currently rebuilding my engine for the third time.

[Lazerviking]

It'll all be worth the trouble once it's back together with ALL of its parts back where they should be. Haha.

[SOHC4 Cafe Racer Fan]

Since you have the cases back together or kind of, I assume you sourced new primary chain and primary chain tensioner.  You can get replacements from Cycle X, including a heavy duty primary tensioner.  I also like Cycle X's heavy duty cam chain tensioner.  M3 Racing also makes a good one.

[Lazerviking]

Since you have the cases back together or kind of, I assume you sourced new primary chain and primary chain tensioner.  You can get replacements from Cycle X, including a heavy duty primary tensioner.  I also like Cycle X's heavy duty cam chain tensioner.  M3 Racing also makes a good one.

Yes sir! Got em all in there ready to rock. They're biting at the bit to get some action.