78/79 cam specs

[trbig]

I was wondering if anyone had a 78/79 book with the specs for the cams. I am running the 78 cams in my motor and want to try the later model cams (3H5). I have recently shimmed it up to specs with the 78 cams, but was wondering if I'll have to re-shim with the other cams.

In the XJ's book, it says the total cam lobe width ( labeled B in my book) is 28.31mm +or - .05mm. If the 78 cams are the same dimensions, the shims should still be fine.

I realize the cam LOBES are different, but you don't shim to the lobe. I'm wanting to know if the back side of the lobes are going to be the same.


Tod

[xschop]

cams

Hey Tr. I have a set of 80 cams from this head, you are welcome to them (unless they make more power, I want them back!) Just kidding....anyways what really is the best head combo? I have read so many diff threads about this subject....Seems like just sticking on an 80 head with 78-79 cams Without boring does just as good as boring out the early or later motor ....Anyways...keep me informed....chop

[trbig]

Thanks Chop. I have a couple sets of those later cams like you have, I have just never tried them. I have heard, like you, that the 78 cams improve performance.... but I have also heard it hurts??

I was wanting to do a swap and see if I can feel any difference... but was worried about the shims.


Tod

[mro]

80 cams...28.31 mm
wear limit 28.19 mm

mro

[79XS11F]

Re: cams

Originally posted by xschop
Hey Tr. I have a set of 80 cams from this head, you are welcome to them (unless they make more power, I want them back!) Just kidding....anyways what really is the best head combo? I have read so many diff threads about this subject....Seems like just sticking on an 80 head with 78-79 cams Without boring does just as good as boring out the early or later motor ....Anyways...keep me informed....chop

So what is different about the 80 head ?
Rob

[Bullet]

From my Yahama factory manual ..

78 cams ( 2H5 )

B - Measurement

28.341 mm +/- .05 mm
wear limit - 28.19 mm


80/81 head has bigger intake/exhaust valves ..

Intake -

38 mm - 80/81 vs 36 mm for 78/79 head

Exhaust -

32 mm - 80/81 vs 31 for 78/79 head


I am gonna use a set of 78 cams on a 80 head .. got no choice .. my 80 cams are toasted from PO'ssss ..

[trbig]

Thanks guys. Sounds like they should drop right in without having to re-shim. I'll check just in case though.

Tod

[egsols]

Bullett,

I might have a spare set of 80/81 cams. PM me if you want me to check.

[John]

Tod, there is a .05mm difference in the intake valve clearence from the 79 to the 80, so right there you will need to change the intake side shims. I believe the 80's are a closer tolerance.

[trbig]

There was a discussion about this when I originally put in the cams as to which of those specs to use... the 78's since those were the cams.. or the later specs since that was the head and valves. I have always shimmed them to the closer XJ specs. That may be one of the problems I am having since I get a puff of blowback into the carb vacuum port where you synch them at.


Tod