Mk1 head on Mk2 engine (CB125)

[Fairies attack]

Will it fit?

Last night the engine decided it wanted to be a 62.5 instead of a 125. So shot the L/H spark plug out.

I have found a head, but my dad says it won't fit is he right?
If so how much for it to be heli-coiled?

[temeluchus]

If you already have the head out it won't cost very much to have it helicoiled.

You can buy helicoil style kits for sparkplug threads quite cheaply if you look.
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Some shite cruiser. Now with guns and FREEDOM!

[Pete.]

They are different. Early engine the pistons go up and down together later ones they alternate, so the cams are different. Teflon Mike says the heads themselves will swap, but I don't think they will - I seem to remember a problem with the camshaft fitting but then that WAS more than 20 years ago.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Fairies attack]

I have all the running gear like cam, rockers, valves and such.

It was more about the bolt patterns and that sort of stuff.

[Pete.]

As I said - I didn't think the camshafts swap. TM will have a better idea since he is currently working on the model. My info is rather old and migh be fuddled.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Fairies attack]

Well thanks any way.
I'll get the coffee maker on, he's probably been writing his post since I made this thread.

[Teflon-Mike]

AFAIK, there are I think about three or four variants of 'Benley' head casting.
Early heads had points in the head ignition; and so they had a completely different head casting to later bikes that have points in the genny, or CDi ignition.
Mostly distinguished by the fact they have old fasioned tappet inspection plugs, rather than a 'pan' rocker cover, as well as points housing on the end of the cam-shaft.
They also had a different cam chain tensioner arrangement, so basically everything from the barel up is different and not part for part interchangeable with later engines, though the entire top end MAY be, interchangeable on the cases.
The later variants had revised camm chain tensioner, and geny cover ignition trigers, and the more usual 'pan' type rocker cover.

Now, as for interchangeability, I have a feeling that there are some variants that had the later style pan rocker cover and genny ignition, BUT had the older cam chain tensioner mechanism, or possibly vica versa....

Its the cam chain tensioner mech that is the critial bit here, you need to check, which tensioner arrangement you have in donor and receptor engine... if they have the same part no's then probably interchangeable, if not, then probably not.

Confuddling, is the CB125 lineology... the MK1 I presume is the '76-82 CB125T 'Twin' with twin shocks, MK2, the monoshock, CB125TD 'super Dream'. '82-92. Later bike had longer production run, with fewer changes. Three main designation changes TD-C, 82-84, TD-E, 84-86, TD-J 87-92... difference between C & E was mainly livery and a revision to the rear light and reflector arrangement, TD-J got tubless tyres and CV carbs, and a different cam.

There was far MORE changes in the model between 76 & 82, and I REALLY do not know or care to know what they ALL are!

However, the T2, which I think is one of the later 'Mk1s' shares a lot of engine part numbers with teh TD-C, and as far as this cam/head issue goes....

ALL CB125's were 180 cranks.... it was only the CD, Benley & CM that had 360 cranks.....

The camshaft from the 17bhp, T2, which has the later points in genny engine, and pan rocker cover, is the same part number as the 'full power' non UK market Super Dream..... as are the valves.

Only cams that wouldn't go into a Super Dream motor would be earlier 'points in head' cam, as that would have the points drive on the end.... not sure if earlier CB125's had that head, CB200 did, or a 360 crank motor cam, from Benley or Rebel.

But short answer is, I don't know!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[Fairies attack]

Tef that is a bloody good post.

I have no idea what bike the donnar head came from just it is Silver so my dad thinks it is MK1, the bike is a E reg CB125tde super dream. I am going to be stripping it tomorrow so will post picks up of the heads.

I may just take it to the place where my GT engine is, and let them heli-coli it and put the bill on my tab. But I would prefer it if this head fits. I have do have 2 to choose from but both are pretty manky and in need for some love.