Author Topic: 750 K2 Strip & Rebuild - help please  (Read 5463 times)

Offline Lobo

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750 K2 Strip & Rebuild - help please
« on: January 27, 2022, 12:04:53 PM »
Hi all, the big difference to this rebuild thread is that I’ll only write when begging for help as I simply can’t otherwise compete - given the skills of most on here.
So, today broke my  ‘750 K2 down into component parts, for no other reason than I want to, ie pretty the old girl up to how the showroom would have had her in 1973. The engine’s running fine; but I will go through it … tho’ not anticipating any major issues. Menno has kindly painted a body set for me, and all other bits will be plated / finished iaw OEM … as far as possible.
Today’s questions please:
(1) Not mentioned in my manual, but I understand the ‘Connecting Rod’ (ie big end) bolt (& nut I guess) are the yield type .. ie one time use only. Are there ANY OTHER such fasteners in the engine that I should be ordering rather than reusing? I’ll assume the old ones are good for torquing down wrt Plastigauge checks?
(2) I failed to remove the Advance spindle from the RHS of the crankshaft - I bottled out after applying as much force as I was comfortable with. (I was working on the assumption of RH Thread and counter clockwise rotation iaw the American forum btw). So… tips please on ultimately removing this with no tears.
Ta for now.
« Last Edit: January 28, 2022, 08:44:35 PM by Lobo »

Offline Nurse Julie

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Re: 750 K2 Strip & Rebuild - answers please
« Reply #1 on: January 27, 2022, 12:15:34 PM »
Con rod bolts can easily be used again if not stretched. The manual also states to plastiguage the shells up on the con rod, so what are you supposed to do, fit a new set of bolts everytime you do them up, nah, I think not.
Im a Nurse, trust me, this won't hurt.....much !!!

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Bryanj

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Re: 750 K2 Strip & Rebuild - answers please
« Reply #2 on: January 27, 2022, 12:44:25 PM »
As Julie sez con rod bolts, and in fact no bolts on the 750, are not "stretch" bolts and can be used again

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #3 on: January 27, 2022, 08:44:56 PM »
Appreciated Julie / Bryan - thanks. Got this ‘duff’ info off a YouTube clip on plastigauging - he called ‘em yield bolts and was adamant one time use only.
Ho hum.

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #4 on: January 29, 2022, 04:02:57 AM »
Crankshaft this time…

1973 Motor, but NOT showing up in my predominantly K0/K1 workshop manual is the bush on the generator side of the camshaft. It looks to me like a mod, with obviously the carrier modified too - comments.

Next up the lobe specs do not tally with those in my manual, the exhaust lobes are more-or-less within spec, but the inlets consistently below spec. The base diameter of all lobes are nothing like book figure…

On a search I found ‘comforting’ news wrt K2+ on the American forum, but again thoughts please.
« Last Edit: January 29, 2022, 04:12:03 AM by Lobo »

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #5 on: January 29, 2022, 04:10:40 AM »
And cylinder head now!

Ok, released all 16 nuts in the prescribed manner, and iaw my manual the head did not lift off.

Boll**cks - the single bolt above the tensioner! Ah, and the 4 hidden bolts beneath the rubber plugs - ie shown in Red. (not mentioned in the book.)

The cylinder head still refuses to separate from the cylinder block, and rather than get all physical I’ve decided to walk away for now. The mating area is currently soaking in WD40…

What am I missing here - no give apparent, it’s as though yet more fasteners are awaiting to be released!

Ta.
« Last Edit: January 29, 2022, 04:15:43 AM by Lobo »

Offline Trigger

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Re: 750 K2 Strip & Rebuild - help please
« Reply #6 on: January 29, 2022, 05:27:26 AM »
The cam shaft and the cam towers have been modified in the past, due to the oil jets have blocked so, no oil to the cam and it cooked.
There are so many different cam shafts fitted to the 750 and too many different measurements / spec but, as above the cam shaft has been cooked so expect lots of damage to the lobs.

All the bolts are out and it is not usual for the head gasket to be stuck. Heat the head a little but, not too much as the heat can easy damage the valve springs and place a soft length of wood up the barrel sleeve and a good whack with a mallet  ;)

Manuals for these bikes is only good for the fire to keep warm  ::) 
« Last Edit: January 29, 2022, 05:36:34 AM by Trigger »

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #7 on: January 29, 2022, 11:32:03 AM »
Thanks Trig. Got the head & block finally separated - nail biting.

The cam news is disappointing - I’m no engineer but it doesn’t look terribly alarming. I’ve had this CB for 10 yrs now, and it’s never given me pause for thought wrt performance, undue noises, vibration, swarf in the oil etc.

So, I’m at a crossroads - spend £500+ on used parts to correct, or put it all back bearing in mind the bike will only likely do 1000 miles pa.

All thoughts welcome.

(How do the earlier cam carriers differ? Can I fit K0 / K1 / early K2 carriers to a 1973 #2241656 engine? Part # 12010-300-20 / - 30 / -40 … with my bike the -40)
« Last Edit: January 29, 2022, 11:58:19 AM by Lobo »

Offline Bryanj

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Re: 750 K2 Strip & Rebuild - help please
« Reply #8 on: January 29, 2022, 06:55:39 PM »
All carriers will interchange, back in the 70's we used to have a man who re-engineered the journals and made split, pegged bronze bushes. As long as lobes were not blue they always ran ok afterwards

Offline philward

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Re: 750 K2 Strip & Rebuild - help please
« Reply #9 on: January 29, 2022, 09:30:34 PM »
All carriers will interchange, back in the 70's we used to have a man who re-engineered the journals and made split, pegged bronze bushes.

Done exactly that on a Phil Read Replica I had
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Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #10 on: January 29, 2022, 11:07:03 PM »
Thanks Bryan; that gives me a few more options. (Ie replacement carriers)

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #11 on: February 12, 2022, 01:20:49 AM »
The strip slowly continues and I note the two Primary chains are differing in ‘slackness’. Is this simply a spendthrift PO trying to save a bob and replacing one chain only… or can there be a more sinister reason? Obviously I’ll be renewing both, but would like to understand the cause…
Ta.
« Last Edit: February 12, 2022, 01:22:44 AM by Lobo »

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Re: 750 K2 Strip & Rebuild - help please
« Reply #12 on: February 12, 2022, 12:00:34 PM »
Primary seems odd that one would wear more than the other, does suggest they've been swapped (or possibly one) at different intervals.

Anyway, it'll sort out with replacement.  To quantify the wear, wrap the chain fully round the bigger sprocket and pinch together,  then opposite the "join" pull the chain out away from centre to measure mm movement. Then do same with new it'll show just how much it's worn for interest.

Offline Lobo

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Re: 750 K2 Strip & Rebuild - help please
« Reply #13 on: February 13, 2022, 11:29:59 AM »
Thanks Nigel - wildo. On the face of it only one chain has been doing all the work I’d guess; lucky the old girl was never thrashed….

Offline Trigger

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Re: 750 K2 Strip & Rebuild - help please
« Reply #14 on: February 15, 2022, 10:28:12 PM »
Check the rubbers in the primary drive sprocket by holding the center and test how much the teeth move.

 

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