cylinder head swap ?

[1fasttrucker]

ok question from all I have resurched I can put a cylinder head from an 80 through 84 yamaha 1100 on a 1979 xs 1100 special,?

I get a head with bigger valves in the 80 -84 1100 head and better flow?
I have hotter cams with my 79 special .

I team up a 80 - 84 1100 head witn a valve job with my 79 cams and I can pick up a low buget horse power or two?

any thoughts?

[GLoweVA]

Somebody might correct me, but with the bigger head, wouldn't you have more combustion area/volume? but then wouldn't your compresion goe down?
I mean the piston can only go so far up and compress the gasses, but if there's a little more room because of the bigger heads, then ie. less compression.

I also read somewhere that the pistons for the 78/79 wouldn't work in a 80/81 becasue of valve clearance. I'm sure some of the gurus here will have a lot of input on this question.

[natemoen]

Yup, the compression did drop in the 80+ engines but the pistons changed as well, I think the later pistons were domed up higher.

[crazy steve]

You can swap the '80-81 head on, but I don't believe you can use the later XJ head because of the YICS passages; at the least, those will have to be plugged. You'll take a slight loss in compression, and you need to check piston to valve clearance because of the larger valves. To get the most gain, you want to swap to the '78E-only ignition advance unit/specs as that has a more aggressive curve.

[BA80]

It doesn't work well if you put the older cams on the newer head. If you change the head keep the cams that go with it. And, you will lower the compression with the newer head on the older engine. The combustion chamber is larger and as Nate said the older pistons don't have as high of a dome.

[cywelchjr]

IIRC someone on here figured out a way to use new style heads with the old cams and got them to work, but I thought it involved slotted cam gears and slightly shifted cam timing to get them to work right. I think it was also tried to mix one older cam with one newer (can't remember if it was old intake and new exhaust or the other way around) that worked ok as well. But the bottom line IIRC was also that it works best to keep the same head with the piston type, as it keeps the combustion chamber and valve timing characteristics the way those very smart guys back in Japan figured it out. The other way is custom ground cams, which I hear can still be had, but you need a set of cams to send in to get reground for you and then tuning will be involved to take advantage of them.

[Incubus]

You are describing the setup I had (OK, still have for a little while) on Succubus, my initial XS11. I used the later head (plugged the YICS with set screws), the '79 cams, and the XJ pistons. Succubus is a screamer. She is practically another class of bike from Incubus, my second - and stock - '79F. Both are '79 Standards.

The drawbacks? I could not ever get Succubus to idle right or to perform well under 3000 rpms. At idle, No 1 cylinder usually didn't fire. I could never make it work consistently. At MOM this year, in a discussion with other members, I pretty much decided that you cannot time the early cams with the later valves to make them work right. It is very similar to problems I have encountered with Honda CB750s when you plug in a racing cam or just a more spirited cam. The valve timing goes off. With a CB750 you get a slotted cam sprocket that allows you to adjust the cam timing. You advance the timing 5 to 8 degrees to make the bike better well at all ranges. I suspect this would also be the case with the XS.

However, a CB750 has only one cam to adjust. I do not feel ready to tackle a project that requires me to change the cam timing on two different cams looking for a sweet spot. Plus, I know of no place that sells slotted cam sprockets for an XS and I do not feel competent to slot some myself. And, as I know of no one who has done the double slotted cam thing on the XS, there is no trail to follow.

Patrick

[crazy steve]

IIRC someone on here figured out a way to use new style heads with the old cams and got them to work, but I thought it involved slotted cam gears and slightly shifted cam timing to get them to work right...

That was Dan Hodges that did that; I went and read his posts as I was thinking about trying this combo. His conclusions were that the late head/early cams combo was worth a few HP due to the larger valves even with the slight compression loss. There was a bit more to be had by slotting the cam gears and fiddling the timing, but it wasn't absolutely needed. The big thing was you want the '78E ignition bits for it's more aggressive curve compared to the later setups, as that's what 'woke up' this combination. He did experiment with mixed cams (late intake with early exhaust I believe) but that basically just moved the power curve around a bit.

[TADracer]

And, as I know of no one who has done the double slotted cam thing on the XS, there is no trail to follow.

I have had slotted sprockets on my 79SF for years. I have not swapped heads or cams so I cannot say what effect that will have with a different setup of cvams and heads. But I have some mild porting and a cut back on the stock valves and I also have larger 36mm Keihin carbs. With my setup I find that the intake cam advanced to 107 Deg. lobe center (thats 6 deg. advanced) and exhaust to 98 Deg. lobe center (2 deg. advanced) it makes the tuning difference I needed to get stout performance from idle through redline. Adjusting the lobe center on the intake cam has the most effect. Drawback is that you can no longer just pull the cams and put them back in as you now need to find an accurtate TDC, a degree wheel and dial indicator so you can degree in the cams each time you touch just about anything up top.

I guess what I am saying is that if I were going to go through all the trouble to change out heads, pistons, cams, etc. I would go the extra step and slot those sprockets.

Oh, and please read the disclaimer that is under my signature below.