1980 Special Head Issues.

[vanimal5k]

I have an 80 Special with broken off stripped out valve cover and exhaust bolts/studs in it. I was wondering if I can use a 78 or 79 head on it, or does it have to be an 80 head? Thanks for your time!!!!!

[D0wn5h1ft]

I have an 80 Special with broken off stripped out valve cover and exhaust bolts/studs in it. I was wondering if I can use a 78 or 79 head on it, or does it have to be an 80 head? Thanks for your time!!!!!

IIRC, you can use early heads (78/79) with late pistons (80/81) but not late heads on early pistons from what I remember. The valves are larger on late heads and I think it will create a collision with early jugs/pistons because the domes are higher. There was a thread where someone did a test to see if the early pistons would collide with late heads and it was close but ended up ok thus disproving the earlier statement. I know there is a bad combination of pistons, heads, and cams that result in valve collision but it's been awhile.

Long story short, keep early cams with early heads and late cams with late heads and you'll be fine either way because late pistons (your 80SG) don't have the higher domes (I think).

Someone will chime in with a correction here in a second.

[rdmcguy]

broken studs

Howdy,..
It seems to me that rather than yanking the head and jumping through those hoops you could locate a GOOD shop to drill,tap or repair those buggered threads, probably cost less than head gaskets and such and less down time as well.....jat

[D0wn5h1ft]

Howdy,..
It seems to me that rather than yanking the head and jumping through those hoops you could locate a GOOD shop to drill,tap or repair those buggered threads, probably cost less than head gaskets and such and less down time as well.....jat

You would still need to take the head off to get those threads repaired...I don't know of any shop that would take a hand drill to an aluminum engine block to drill out heat stressed, broken off steel studs...

Best case he would need to take the head off, jig it up on a drill press, and use some hardened bits. Even then there probably won't be any aluminum left to re-tap once you get the old studs out so you'll need a helicoil or some other sleeve. That wall thickness of the valve cover bolt holes is really thin too so there's not much material that can be relied on later...

Seems like a lot of work to do when you can just bolt on a new (used) head off of ebay for $100 plus the cost of the head gasket if it can't be reused.

[rdmcguy]

lucky I guess

I guess I am just lucky,I have a great shop here that has done similar repairs for me including drilling and tapping the bolt holes that hold the cam in....while still in the bike.....old school mechanics..

[motoman]

IIRC, you can use early heads (78/79) with late pistons (80/81) but not late heads on early pistons from what I remember. The valves are larger on late heads and I think it will create a collision with early jugs/pistons because the domes are higher. There was a thread where someone did a test to see if the early pistons would collide with late heads and it was close but ended up ok thus disproving the earlier statement. I know there is a bad combination of pistons, heads, and cams that result in valve collision but it's been awhile.

Long story short, keep early cams with early heads and late cams with late heads and you'll be fine either way because late pistons (your 80SG) don't have the higher domes (I think).

Someone will chime in with a correction here in a second.

Before you go and mis-informed a member , maybe you oughta read the RECENT situation that 3Phase went thru just prior to the Colo. rally. No offense intended, but unless you've BTDT, your chances of mis-information runs high.

[cajun31]

You might

want to read this interchange thread put together by CrazySteve.

http://www.xs11.com/forum/showthread.php?t=36652

[3Phase]

Danger! Will Robinson!

want to read this interchange thread put together by CrazySteve.

http://www.xs11.com/forum/showthread.php?t=36652

And Steve's got the major technicality covered: "Going the other way will raise compression, but again you need to check piston/valve clearance."

The minor technicality compared to a possible piston-to-valve collision is the exact year/model the early 2H7 cylinder head came from because the exhaust header collars are different.

The '79SF has the shorter exhaust header collars and studs like all of the '80 and '81 3H5 heads and the XJ's 10M head so a '79SF head will work with a '80SG if the valves will clear the pistons.

A '78E (I believe) or '79F 2H7 head will work with a '80SG if the valves clear the pistons but they will not allow the exhaust system to bolt on without changing the exhaust studs.

.

[D0wn5h1ft]

Before you go and mis-informed a member , maybe you oughta read the RECENT situation that 3Phase went thru just prior to the Colo. rally. No offense intended, but unless you've BTDT, your chances of mis-information runs high.

Kind of clearly said that I wasn't 100% sure and that he should wait for a second opinion. Missed the "recent" situation someone went through but I did read a thread about mixing pistons and heads (that ended up with enough clearance in the clay) that I tried to point him to search for....never claimed to be sure of or even confident in my answer.

[cajun31]

Hey Vanimal

I remembered this thread from earlier this month. It seems that Tcoop has done what you were asking about.

http://www.xs11.com/forum/showthread.php?t=42323

[WMarshy]

Kind of clearly said that I wasn't 100% sure and that he should wait for a second opinion. Missed the "recent" situation someone went through but I did read a thread about mixing pistons and heads (that ended up with enough clearance in the clay) that I tried to point him to search for....never claimed to be sure of or even confident in my answer.

To elaborate on his comment, I believe what he is trying to say is if you dont have first hand experience with it or are not 100% confident in your answer (and can list your source) dont make the suggestion. It would be more useful to post a link to the info he seeks or tell him to keep searching.

Providing a reply with a lot of "I think I remember reading" can cause more harm than good. People read it and for some reason it will be the only thing they remember and can cause more damage, or worse it get repeated as fact...

[D0wn5h1ft]

To elaborate on his comment, I believe what he is trying to say is if you dont have first hand experience with it or are not 100% confident in your answer (and can list your source) dont make the suggestion. It would be more useful to post a link to the info he seeks or tell him to keep searching.

Providing a reply with a lot of "I think I remember reading" can cause more harm than good. People read it and for some reason it will be the only thing they remember and can cause more damage, or worse it get repeated as fact...

Point taken. I'll just refer to a specific thread next time or at minimum provide criteria to use in the search function.

[tcoop]

I did use a 79F head on my 80LG using the headers from the LG. To make this work I added a lock washer under the exhaust nuts. This may be to redneck for some but I have been running it that way for over a month with no problems. Not sure if over time stress will cause this set up to fail. THIS IS NOT AN ENDORCMENT TO DO IT THIS WAY.

This is how I have it setup.


Replacing the studs is the best solution.

[3Phase]

That looks great, Ty!

The 'wrong' exhaust studs in the head just adds an unexpected stumbling block to putting the bike back together but anyone getting close enough to actually notice and care about washers under the exhaust nuts should change the studs for you or at least offer to buy you dinner or something.

.

[motoman]

check your PM's 3Phase.