1986 VFR 750F Motor Rebuild

The purpose of this thread is to document the rebuild of RC24E motor on my VFR 750. Advise and comments relevant to the rebuild are welcome and appreciated. I will update this first post in the thread with my progress.

History:
I bought the bike recently as a project with a known gear problem. 4th Gear likes to pop out on acceleration. The previous owner bought the bike like this and rode it around skipping 4th gear as he rode. He bought the bike in this condition and could not explain to me how it got this way.

This VFR has 62,000 miles. In diagnosing the problem I changed the oil, and checked chain tension and alignment. During the oil change I did noticed fine metal flakes in the oil. Judging by the discolored engine cover, my best guess is that the bike went down on the left side, and the shift fork probably was bent.




I got my hands on a complete low milage gear cluster and shift forks from a 700. The transmissoin should be identical to a 750. To change out the transmission on these motors, the book says you have to pull the motor, remove the heads and split the case. Since I will be that deep in the motor, the plan is to check all tolerances and perform a rebuild.

Step one. Clean.

Warmed the bike up for fluid change and compression test.

plastic and tank gone.

So I was not able to do the compression test for an hour after I warmed up the bike. The motor was still warm. All reading are around 150PSI and the plugs looked good.

Carbs removed.

Radiator, headers, and oil lines removed.

shifter position marked.

I know I know...need a real stand.

Water pump cover removed.

Water pump pulled.

Sheered a bolt when removing the kickstand.


Thermostat removed. Getting ready to drop.

Dropping

Dropped

Finally on the bench. Im 4 hours in at this point.

Valve covers off and cam removed

Cams ready for tolerance checking

1 and 3 pistons and cylinders look good. I expected more carbon for 62k miles.

2 and 4 look good as well. No scoring on piston walls..no glaze either. I can still see the cross hatch.

head from 2 and 4 (front)

Valves from 2 and 4

Head from 1 and 3

1 and 3 Valves.

Need to do some clean up here.


Got stuck on special lock nut for clutch basket. Looks like I need another tool. Thats it for this weekend.

-Ty

 

Get the gears undercut and you won't strip gears again.

 

so what exactly ARE undercut gears?

 

clymers has a step by step breakdown of engine...not a lot of pictures though.

 

Hey it's SHONOUGH the Shogun of Harlem
What ever happened to Bruce Lee Roy??

 

The Honda service manual is pretty detailed on this.

 

Google gear undercutting. Dave Dodge www.drp123.com does them.

 

gear undercutting

I appreciate the advice on gear undercutting.

I just got off the phone with Greg Spears from Spears racing (the 2nd link when you Google gear undercutting). They do gear undercutting, but it is not cheap....Around $800 for up and downshifting. He advised that, given my budget (Id like to keep the rebuild under $1000), I should get the motor apart and evaluate where Id like to spread the cash.

Greg sounds like a great mechanic. I’m looking forward to working with him on this rebuild.

 

Hey, sounds like a great project. I've had to replace the head gaskets on my 700, all I had was the Haynes and it's still running , but that's as far as I've gone (first bike too, no prior experience). The cams weren't too hard to get back on since they're gear driven, and the valves are adjusted by a screw and not shim like the later models.
Also when you take it apart you might want to order all new washers/gaskets for the cooling system if you take any apart, I found the old ones wouldn't seal again for me once I'd broken the contact.
Hope this helps, good luck

 

Hey congratulation, it looks good, i

 

Thanks for the insight. I was a little concerned on the gear re-assembly.
Still considering porting options.

-t

 

My wife and I are just finishing re-assembling her Hawk from a full tear-down and splitting of the cases. It's not hard, just pay attention, and take notes.

We set up a big banquet-style folding table next to the work area and covered it with butcher paper. As each part came off, it was labeled on the paper (after wiping off most of the oil).

With our limited time to work on things, it's taken a year start to finish, but now we're finding that between the well-labeled parts, and the fact that we have a zillion photos of the tear-down, it's not been too hard.

Only resource is the Honda service manual. I'd take them over a clymer or haynes. But you might find that getting all 2-3 manuals available will help (mainly for photos). Sometimes the honda manual is lacking in diagrams on how things are supposed to fit together.

And btw, it's looks like a beautifully clean bike!

 

You have a CBR600F2 front end there(forks/triples/wheel/fender/etc), and likely an F2 rear also. If it has "all the right upgrades", then it should also have a non-Honda rear shock, and aftermarket springs in the front - Racetech Gold Valve Emulators would be nice too...

 

If they are F2 brake rotors they've definitely been drilled out.

If you want to ride sometime drop me a pm, I'm just up the road in Rocklin. Nice looking bike. :thumbsup:

Did Greg say he would work on these old V4's? The website says they're dedicated to V twins now.

 

Having trouble finding a gasket set. sheesh

 

Head gaskets

It is to late, but you dont need to remove the heads for this repair and the head gaskets are REALLY expensive.The fourth gear failure is pretty common and is due to passing , going from sixth to fourth and getting on hard while down shifting.

 

It looks like you may be right. The factory manual is telling me to remove the heads. I figure Ill get some compression back with the new rings and check the valve seats while Im in there. The top end kits are much cheaper in Europe btw.

Thanks.

 

Hey TC,
where did you get your engine gaskets ? i went to my local dealer and they said that they are discontinued ?

 

I'd go with Dave Dodge. He's got a gearbox of mine right now being undercut. He charges $400 and specializes in early V4 Honda work. You won't get better quality work and the price is the lowest around.