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"78 XR75 Head Swap

3K views 14 replies 3 participants last post by  firepower354 
#1 ·
I have a 1978 xr75 with scored journals on the head, Cam is also spent. Will a 1980 xl80 head and cam interchange onto the '78 engine? Looks visually close but don't want to make a pricey mistake.
 
#3 ·
Can't remember which, but XL heads also have a head stay mount on them that the XR's don't (the 100's do for sure....maybe the 80's dont....code on head is 152). The XL head is a drop in like FP said.....go with a 100 cam or buy aftermarket and add a pipe and carb w/opened up airbox for good performance, if that is what you are looking for.....
 
#5 ·
Thanks for the replies. I will be tearing down the xl this weekend, fingers crossed that the head is in better shape. If memory serves, that engine jumped time so likely bent valve but hopefully no scoring.

Question on the 100 cam - will a stock cam from a 2004 crf100 fit? I upgraded my 100's for at-home flattracking and have two stock cams sitting around.



The xr75 will be a rider, want it nice but not restoration-quality. I'm also working on a 1975 xr resto project but not finding the parts I need at a reasonable price so it sits... So many projects and so little time.



Terry, I'm the guy who traded you the xr100 engine for the Pitster parts last year - man, that bike is fun!
 
#11 ·
firepower354 said:
Head stay on a 75/80/100 series? I thought the old 100/125 jobs were all with one? Old guys:rolleyes: lol


Absolutely! The first version XL's to not use the old-style (SL/CL/CB) 100 engines, I think in 1979-80, maybe 81 as well, had a cast in head stay lug to tie it into the frame....I may be old, but.....err, uhh....what was I gonna say?!



Oh yeah! That I can remember stuff....sometimes, well, alright, occasionally!!
 
#14 ·
firepower354 said:
Yeah, that's what I'd meant. the head-stay versions won't bolt to any XR or other 75/80/100 series "small block" upright:)


No, What I meant was the 79-85 XL100S Honda head HAS A HEAD STAY.....and, bolts on later XR/CRF100/80 cylinders.......check the fiche....you, you, you,....non-believer!!! lol



patiently awaiting the crow for lunch bro....ha!
 
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