Cracked head, replace 72 with 75 head?

[TFR Aussie]

The lock nut on my left exhaust valve adjuster has come off, gone under the cam and cracked the head below the cam... Bugger @#$%
I have been doing this for years and my old Ducati has the same sort of adjuster and never had a problem with either before over decades of ownership.
I have a couple of questions.
1 - can you remove the head without removing the engine from the frame?
2 - can you remove the cam without breaking the chain?
3 - I have a spare 1975 head (#447 104 514), will this fit on a 1972 engine (#s650 129 120)?

This is to show where the crack is using the spare head.

 

[jpdevol]

I have a couple of questions.
1 - can you remove the head without removing the engine from the frame? Sorry, No
2 - can you remove the cam without breaking the chain? Yes, remove cam cover & bearings from cam
3 - I have a spare 1975 head (#447 104 514), will this fit on a 1972 engine (#s650 129 120)? Yes, with attn. to gasket sealing areas


This is to show where the crack is using the spare head.

 

[Signal]

1 - can you remove the head without removing the engine from the frame?

No the motor will need to come out.


2 - can you remove the cam without breaking the chain?

Yes, loosen the adjuster and wiggle the bearings out of the holders. Remove the bearings ( they Slide off) and giggle the cam a bit and work it out under the chain.


3 - I have a spare 1975 head (#447 104 514), will this fit on a 1972 engine (#s650 129 120)?

I am pretty sure it will but don’t know for sure, others on here will know for sure. The cam timing sprockets changed from 34 to 36 at some stage replace like with like and you will be good there.

Good luck, it is interesting I have seen adjuster nuts come off a couple of times, both were number 1 inlet looks like it was the same for you.

 

[Jan_P]

Using another head .Personally I would be hesitant to do it.
Major manufacturers have standardization departments
Keeping down the number of parts ..to have in storage
One can often crosscheck in the parts lists online between years and models
fex engine Blocks can have the same part no over many years and so on
Clutches also have parts that are the same over years others not.

a 1975 part has taking in Considerations from the ..field .. market and would normally have evolved.
redesigned

So if not the same part No ... there is a difference ..just a question of how big.
Not saying it is impossible it can only be a minor difference.
But considering the work involved Engine out new gaskets -- seals - adjustments
In again .AND then after a few turns on the engine realize Aeehh S*it did not work
and then do it over again

Personally I would search for the right part .. Not at the moment knowing the availability in AUS or prices
But would be surprised if it is over $ 100 US
I would pay that ..price

 

[GLJ]

There is the option of have the crack welded.

 

[grizld1]

Yes, the 1972 (XS2) head can be replaced with a 1975 head with no issues. Move the left cylinder exhaust rocker and valve cover from the old head to the 75 head, be sure to use the 75 head and head cover together, and use the 72 camshaft if it survived. The 1975 camshaft sprocket is not compatible with the 1972 crankshaft sprocket or cam chain tensioner. The 1975 cam can be used if the 1972 sprocket is installed on it.

 

[TFR Aussie]

Yes, the 1972 (XS2) head can be replaced with a 1975 head with no issues. Move the left cylinder exhaust rocker and valve cover from the old head to the 75 head, be sure to use the 75 head and head cover together, and use the 72 camshaft if it survived. The 1975 camshaft sprocket is not compatible with the 1972 crankshaft sprocket or cam chain tensioner. The 1975 cam can be used if the 1972 sprocket is installed on it.

Cheers Griz, I will look at getting the 72 head stitched first just looking at options at the moment.
And just to check what was said above that the engine has to come out to remove the head?
Also, why should I "Move the left cylinder exhaust rocker and valve cover from the old head to the 75 head"?
Sorry for all the dumb questions.

 

[Grewth]

Cheers Griz, I will look at getting the 72 head stitched first just looking at options at the moment.
And just to check what was said above that the engine has to come out to remove the head?
Also, why should I "Move the left cylinder exhaust rocker and valve cover from the old head to the 75 head"?
Sorry for all the dumb questions.

Your '72 should be a XS2, these had a cable opperated decompressor built into the LH valve cover - hence the "odd" four 8mm studs instead of 3x6mm as used on the XS1/XS1B.
The factory soon found that the decompressor wasn't really needed, so it was deleated for '73, but the modified castings with the four 8mm studs remained until the end of production in the '80's

 

[gggGary]

the engine has to come out to remove the head?

Yup unless someone has previously removed the studs from the crankcase and slotted the ends for easy removal there's no way to remove the head til the motor's out.

Move the left cylinder exhaust rocker and valve cover from the old head to the 75 head

If you want to retain the compression release. More of a fashion thing than needed for operation. I've found that the little bump for the compression release also stayed on the rockers for years, maybe til end of production.

 

[5twins]

The rockers with the "bumps" were used for a few years after '72 but eventually the "bump" disappeared. I'm thinking that maybe Yamaha had a large supply of the "bump" rockers (more than needed for just spare parts) so wanted to use them up.

 

[TFR Aussie]

Your '72 should be a XS2, these had a cable opperated decompressor built into the LH valve cover - hence the "odd" four 8mm studs instead of 3x6mm as used on the XS1/XS1B.
The factory soon found that the decompressor wasn't really needed, so it was deleated for '73, but the modified castings with the four 8mm studs remained until the end of production in the '80's

The decompressor has been deleted on my 72. Eng#s650 129 120 which according to the lists I have make it a 72. Looks like a late number though.

XS2

306

S650-100101

1972

Brilliant Red