Engine VIN restamped, BUT DOESNT MATCH my F2?!?

[CR92]

Put a post up here 2 days ago with some confusion over VINs on my CB750
I have an F2 supersport, so I'm lead to believe. Frame VIN CB750G101 etc
However, the only thing that doesn't match is the crankcase engine VIN
RC01E201...
From what I have researched this is not an F2
And the stamp has clearly been ground out, restapmed, pretty poorly, with a VIN that doesn't match the F2 frame

I'm new to CB's and wish I knew what was going on but that's why I posted here, need some knowledge from someone who might know or have dealt with a similar issue
After market parts? Different crankcase? Please tell me not different engine
The cylinder head, cover is SOHC so please tell me why the bottom half doesn't match.

Or does it and am I just being a dumbass

Cheers

Conor

 

[dirtdigger]

posting some pictures would help out a bunch.

 

[CR92]

Hope this works dirtdigger, apologies for picture quality

Cheers

 

[amc49]

RC01 is generally a DOHC engine prefix for K bikes..................

 

[CR92]

Amc49, is there anything different about the K and F crankcases? Or can they be interchanged and hopefully solve why I have a K stamp, because I don't have any other parts on this engine that make it DOHC or not to my knowledge anyway, it's all SOHC

 

[dirtdigger]

So this is a sohc bike or a dohc bike? If its sohc then yes there are differences between the k and f but that is not a sohc motor stamping. Can you post some pictures of the bike and motor so we can figure out what you have? I am confused right now.

 

[CR92]

So here she is, F2 supersport (I hope) from the first post I said the frame number was cb750g** so this matches up with the F2, right?
And yeah, the engine VIN has just thrown me off, but you can clearly see it has been grounded, and restamped, it doesn't look original cast

 

[CR92]

Here's some pictures of the block

Cheers

Conor

 

[amc49]

The motor is definitely a SOHC, the VIN pad for DOHC is past the right end of starter and between starter and clutch, the SOHC pad is behind starter between it and the drive sprocket.

K and F SOHC are different motors.

K and F DOHC are identical engines.

https://www.motorcyclespareparts.eu/honda-parts/honda-model-prefix.aspx

Scroll way down the alphabetical list to find RC01, it shows some as being '78, some DOHCs were out in '78 but were '79 models.

 

[dirtdigger]

Definitely not a correct number for the sohc motor, should start out as a cb750. Dont know how they are with engine numbers over there but its not as issue in my state anyway, they could care less. If its an issue there you may have to look for a different set of cases. If you send me a picture of the bottom of the cylinder head I can tell you if its a k top end or a f2 top end, there should also be a 410 cast in the top fin of the cylinder head if it is a f2 if it is a 392 or no number then its a k

 

[CR92]

Cheers guys for your help! Starting to get to the bottom of it!
I'll post some pictures dirtdigger and hopefully be able tell what I've got! I'll keep an eye out for that number in the top fin aswell!

 

[K2750tracy]

It looks like someone ground off the original numbers and stamped in some new ones, probably to match up to a title they had for a DOHC bike.

 

[CR92]

Okay, so kinda good news and some confusing.
I checked the top fin for the 410 marking and yes it does it! Brilliant F2
However, another post on this forum suggested different engine oil ports on the underside of the cylinder head.
I've checked against mine and they seem to match up to a K type engine.


Can anyone confirm

And if If this is correct will they work together, the two different types

 

[CR92]

My guess is no, oil ports blocked off could mean oil trying to pass through and being blocked at the cylinder head.
However, might be wrong!

Cheers

 

[CR92]

Definitely not a correct number for the sohc motor, should start out as a cb750. Dont know how they are with engine numbers over there but its not as issue in my state anyway, they could care less. If its an issue there you may have to look for a different set of cases. If you send me a picture of the bottom of the cylinder head I can tell you if its a k top end or a f2 top end, there should also be a 410 cast in the top fin of the cylinder head if it is a f2 if it is a 392 or no number then its a k

What do you think dirtdigger, can you make out why it's a F2 rocker head but got the cylinder head from k? Unless the person that posted about the f and k cylinder head differences was wrong.

Please help! Haha I'm pulling my hair out trying to sort out what's what

 

[CR92]

I apologise to the amount I have been posting myself on here,
I've been working nights straight from the 23rd through to the 2nd, I'm a bit bored and thought sod fixing my bike up are getting me through it haha

Anyway, I've been reasearching like crazy to try and find the answer to my problem, when I found a picture of the F2 gasket. On the picture you can clearly see fit outa made to fit in line with my cylinder, so this means it must ALL be F2!
I don't know if different countries had different varieties of cylinders and I've stumbled across a picture that I thought may have been K?!
But by seeing this it does allow me to think that the cylinder and cylinder head will match up, and my thoughts concerning an oil passage problem have been put to rest, hopefully.
I hope to God I am right because I've had enough of trying to work out what this bike is haha
Please please please let it all just be F2 with some idiot who stamped a K number on it.


Thank you

 

[CR92]

"You can clearly see CUT OUTS"

apologise further for spelling mistakes, all done on my phone in the middle of the night haha

 

[dirtdigger]

You definitely have a F2 head but definitely have a K cylinder. You can make these parts work together but not in stock form. If you just bolt them up you will have oil leaks as the oil drain backs are different between the f and the k. You can make them work with some machine work in the head, you press brass sleeves in couple of the cylinder stud holes. I have some pictures in one of my photo galleries on here because I have done it. Now what are you going to do with the motor? complete rebuild with overbore pistons or using stock pistons you have? If you put a f2 cylinder on k cylinder and piston you will have low compression ratio, you need specific pistons to work with the f2 head. If it was me I would either get a k head and pistons and match the cylinder or get a F2 cylinder and pistons to match the head.

 

[dirtdigger]

Its seems a lot of mixing and matching went on by the previous owner and most of the time it isnt done right. The wrong engine vin stamping raises a lot of questions and is a big red flag that they had no idea what there were doing.

 

[CR92]

Cheers dirtdigger
There's definitely no chance that the cylinder matches up to the head, it's just hard to come to terms with when the bike was purchased as a whole. Previous owner stripped engine complete and I brought it off him in bits.
All in all, bit of a pain in the arse!
I would like to bore it out to 836cc
If I'm honest I'm not sure if It will be less time consuming and cheaper to just buy new barrels?