Basket case to Cr750 rep.....hopefully!

[Bryanj]

If the CRANK CASE codes are the same the shells can be transfered

[Trigger]

You will have a lot of measuring up to do. Make sure you keep the con rods in the right weight set.

[burchy75]

Managed to find all the codes that I think I need to work out what bearings I’m going to have to pop in.  The main crank code was a right pig to find and then read.  You needed just the right light and angle to see all the etched letters and numbers but after a few minutes of juggling crank and torch I got there.

So the numbers that came back are BBBAA from the K1 cases, J ACCAA P L4444 from the KO crank itself.  The rods themselves were all 2F.

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Now from the table in the book I have here I’m looking at all green bearings for the rods themselves – if they are all in spec.  The original green bearings themselves all looked in good nick when I split the cases so may be able to reuse possibly once I've checked clearances

Trying to work out the rest it looks like I’m going to need 10 x green (possibly only 2 if I can reuse the original rod bearings), 4 x brown and 4 x yellow but I’m going to go over my 5 min calculations to make sure it’s all correct before attacking the thing with Plastiguage.  With the play in rod 1 I think this might need a different bearing itself but the plastiguage will help I guess

I’m kind of thinking of getting one set of green, brown and yellow bearings for now so I have test each point and have a new size bearing if one or more are slightly out of one specific size, if that makes sense.  I can then double check everything before ordering my final bearings.

[Trigger]

The rods are from a later K, maybe K2 onward, make sure you know where all the rods came from on the crank and the right way round, if looking to re use shells 

[burchy75]

Oh bugger, I thought the rods were K0 as they came straight out of the K0 engine, oh bugger, that means the cases have been split before so could be loads of unusual stuff in there.

As for the bearings themselves I may end up just going with new bearings all round just to be on the safe side.

[Trigger]

What is the engine number ? Is it a K0 head and barrels ?

[burchy75]

The engine number is CB750E 1040029

As for the head and barrels, have absolutely no idea what year they are from, is there any way of finding out?

[Trigger]

Shape of the head and what type of oil jets. The barrels are a different shape to the later. Early barrels have a flat at the front and the later is rounded . [ Guests cannot view attachments ] [ Guests cannot view attachments ]

[burchy75]

Turns out I have two, the one that was on the K0 cases was an earlier one and I have a spare 'rounded' one that is currently sat on a K6/K7 engine

[Trigger]

Sounds good, what type of oil jet is in the head ? This will tell you if the head is a good match for the barrels.  Am i working too fast for you 

[MarkCR750]

Good luck with the project, if you have no luck with the top yoke I have a cast one that just needs one face machining.

I’m struggling to upload the photos, used to be able to email to myself then save back to my phone to get the file small enough for the forum but now it’s saying it’s the wrong file type 🙄, pm me your email address and I’ll send the photos 👍

[SteveD CB500K0]

What sort of photo files are you trying to upload? I can soon add another variant to the “allowed” list.


Sent from my iPhone using Tapatalk

[burchy75]

Sounds good, what type of oil jet is in the head ? This will tell you if the head is a good match for the barrels.  Am i working too fast for you 

It looks like I have 4 of the early style heads and two early barrels in the box of bits that I bought, this includes the barrels and head that came off the KO engine itself.  Hopefully these should be ok to go straight on the K1 cases I have here.  It turns out I also have 2 later style heads as well, which I may end up using on the 76/77 engine I have here (at a later date).  The spare engine cases have an engine number of CB750E 2547990, which I believe is an 1976 F2 engine number and not a 76 K as I'd originally thought - can anyone else confirm this?

[BigAl (Alan)]

The engine No. 25***** is the F1 motor March 75 to Nov 76

[burchy75]

I've been trying to make some headway with the carbs I have here.  As I have some rebuild kits on order for them at present I needed to get the old needles out of the floats, however looking inside them there was a world of hurt waiting for me with the tiny pan screws that hold the rod mechanism in place.

Now separate to this I'd heard about JIS head screwdrivers and their advantages over Philips heads with old Japanese bikes and having rounded a few of the pan screws in the past I thought I'd have a blast at grinding down a standard Philips to see if it made any difference in getting the screws out.

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Wow, is all I can say.  30 seconds on the grinder to take the tip off and angle the 4 edges a little and all 8 screws came out without any drama at all, even the two that were caked in rust or something equally as nasty.  I'm probably preaching to the converted on here as many of you have no doubt already done this but having cursed (a lot) when I've rounded screws in the past this felt like a nice easy win 

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I want to get the carbs rebuild if possible and then turn my attention to the frame that is currently dangling from the garage ceiling.  I'd like to bolt up some of the rear end and get the forks on, more to see the stance of the bike than anything else as I've only ever seen it in boxes and getting something that resembles a bike, even in these early build stages, will hopefully put a smile on my face and spur me on.