A tale of two heads

scotts · Posted: October 28, 2009, 9:39 am Post subject: A tale of two heads

I have a running '78 engine with cracked fins on the head.
I have a non-running '75 engine that is frozen. The fins are in great shape.
I'd like to swap the heads when I do a general freshen up on the '78.
My main concern is what happens to the spring tension when valves are stuck in the same position for so long?

I assume that at the very least I'll need to lap the valves and bead blast the head.
Can I swap out the best parts of each head (cam, bearings, springs, rockers, etc.) over to the '75 head and make one good head?
I have not pulled the head off either bike yet, so no visual inspection at this point.

jayel · Posted: October 28, 2009, 10:58 am Post subject: Re: A tale of two heads

the complete heads are the same part numbers as far as I can see, just go thru a parts site and compare numbers

scotts · Posted: October 28, 2009, 11:26 am Post subject: Re: A tale of two heads

I know that the heads will physically swap. I was asking more about springs and valves in the '75 that have been held in the same position for years.
Could I use springs, rockers, valves, etc. out of the '78 head and put them in the '75? Assuming they check out and are in good shape....

Srinath · Posted: October 28, 2009, 11:51 am Post subject: Re: A tale of two heads

scotts wrote:

I know that the heads will physically swap. I was asking more about springs and valves in the '75 that have been held in the same position for years.
Could I use springs, rockers, valves, etc. out of the '78 head and put them in the '75? Assuming they check out and are in good shape....

When the head is out get a 3 angle valve job and re do the seats etc. That should get it all nice and new and sealing up. The springs and seats should be OK as long as its had no exposure to the elements. The seals should be replaced but they cost very little.
I did that to a GR head that was rusted. Seemed good when done but I am yet to get it on a motor. Springs etc seemed OK.
Cool.
Srinath.

gordo · Posted: October 28, 2009, 3:39 pm Post subject: Re: A tale of two heads

scotts, most machine shop's have the tool used to check spring pressure's. Spring's are usually checked in two spot's, one being at the 'set' height, the other at 'open' height. There is a spec for both height's, can be found in a clymer's or the knuckle buster's site. Or, you could just replace the whole set because being pressed open for so long doe's make them weaker. Your other head's have cracked fin's, so if they have been in use, they should be ok.

oldkarkid · Posted: December 17, 2009, 12:34 am Post subject: Re: A tale of two heads

Agreed with Gordo, if you are in doubt, swap your springs too.

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