Rebuild opinions wanted!!

[trbig]

OK... I was wondering what the general opinion would be if you were in my shoes. (But hurry up... it's the only pair I own!) As many of you know, I am currently running a 78 XS motor in my XJ with the bigger valved head from the XJ and the cams off of the 78. The compression in my #1 cylinder is about 20 lbs lower than the rest, and it has developed some noise lately that sounds like piston slap. It hasn't gotten any worse in the last couple thousand miles, but I figure it's time to get a rebuild during the coming winter. I have the spare XJ motor, but it would need rebuilding also. I plan on having this bike from now on, so I have already decided on the 1174 kit to allow another rebuild in the distant future.. (Or give my kids enough room to do so after I'm gone! )
After all that, I finally get to my question... lol. Would you rebuild the XJ motor which is a slower than the XS, but be able to continue riding during the process (I ride all year, rain snow or heat) or just take time away from it and get the XS re-done? I am really liking the crank lightening that I read about on Ape Racing Products website and thought about sending mine there, but I am wondering if it would really help any if I am going back with everything else pretty much stock. I also wonder if it would make the crank weaker which is dang near indestructable in these things as-is.
For once... someone actually wants to now what your opinions are!!

Tod

[mro]

Dependability,
I'd keep it near stock, but loose the yics

Want more power, do it similar to Maximan's.....



mro

[GNEPIG]

.. having the crank turned is cool, it will cause your engine to rev alot faster, in return causing you to realize your peek power faster... the the down sides to the lightened crank is more vibration, rear wheel traction will suffer especialy in wet conditions and how it will be way to easy to over rev your motor[like when you miss a shift].
..if you have two bikes, one near stock and one for play, having the crank turned would be fun. if it was my only ride and my main source of transpertation, i would probly leave well enough alone and spend your 4- 6 hundred bucks for a nice paint job.
.. you are going to like the way your bike feels after the big bore kit.

[DiverRay]

Tod,
I'd have to agree with mro. Maximan has his bike close to stock, with the yics head. He is pulling a LOT of power and bottom end from the bike, and it's very docile.
I would rebuild the XJ motor, and put it in once done. A little work, and jetting, and you would have a bike that will go another 100K miles, and be quick at the same time. JMHO.
Ray

[trbig]

Hmmmmm so far that's one Yea the YICS.. and one Ney! As for lightening the crank...pardon my ignorance again please... if it is balanced correctly, why would there be any more or less vibration? A truck tire that's balanced correctly shouldn't vibrate any more than small car tire balanced.... more inertia yes... but I don't understand why a lighter crank would. As for price... APE prices say 225 for the lighten and balance... and 60 bucks for the magnaflux... so under 300 bucks not counting shipping.

As for the motors.... all things being equal... wouldn't a rebuilt XS be stronger than the same rebuilt XJ motor? I tapped, threaded, and plugged the YICS ports on the head I am using, but would be easy enough to unplug. I was just under the impression that the early XS motors were the powerhouses.

Tod

[DiverRay]

Tod,
The early motors had the power from the cams and slightly higher compression. You can rebuild the '82, go ahead and block the yics, run a hotter cam, or do as Maximan did and have the cam gear machined so you can adjust the cam timing. The crank and rods should be balanced, but if you lighten, you remove the mass that helps keep the vibrations down, and possably weaken the crank just a little. On the XS/XJ, I don't think it would hurt, but it is your money.
The XS/XJ are built on the SAME bottom end, so they are equally strong. the larger valves on the XJ make it the head you want to use, with the early cams. That with the cam adjustment and the 1179 kit should give you close to 85 RWHP.
Ray

[81xsproject]

just my personal opinion, but like, I think it was Maximan, said get the 1196 and and a spare set of jugs off ebay for backup.

[mro]

so under 300 bucks not counting shipping.

Hmmm...........

Lighten crank???, or have head done???..........
What kind of exhaust you running???


mro

[trbig]

I still have stock exhaust. Only thing I have done is put the pod filters on it along with the 78 cams in the 82 head. I am still sticking with the 1174 kit. As hot as it gets in the summer here and the sometimes stop and go traffic I have had to ride in, the extra heat build up of the bigger bore deters me a bit from it.... as well as the option to be able to do another bore on it in the future if needed. The XJ motor I have has the attachment and lines for an oil cooler which will definately be installed... I just need the radiator part.
I have a local shop that will redo the head for me for 100 bucks labor, and he is going to bore and hone all the jugs for me for 150 bucks when I get the pistons for him to measure.

Tod

[81xsproject]

Maximan said he got his cooler from just some normal auto parts store. You might check into that...

[GNEPIG]

if it is balanced correctly, why would there be any more or less vibration? A truck tire that's balanced correctly shouldn't vibrate any more than small car tire balanced.

.. what's going on inside your motor is not like your car or truck tire. as a piston is slung towards the head at a high rate of speed the counter weight [or cheek] that is on your crank moves in a different manor to counter the violent movement the piston is making moving away from your crank then stops and then snatches the piston back towards the crank. in it's stock form, your crank, conecting rods/rist pins and pistons are balanced as a set. make your cheeks lighter and you will have less weight to counter the weight/force of the piston/rist pin/con rod as it is moving at super speed towards top dead center and stops suddenly. less weight on the crank= more vibration, unless you can figure out how to make the top end parts lighter as well.
.. i am not saying dont do it, i'm just letting you know some of the consequences.
Falicon was going to charge me about 450 bucks to have my crank lighten about 7 years ago. i didnt know it was so cheap now.

[TopCatGr58]

Hey Tod,

Do you remember our PM discussion about finding head gaskets?? I was going to make an arguement about not being able to use the YICS anyways since the special XJ gasket isn't available from Yamaha anymore...but then I found it on PNM!

The XJ styled gasket with the openings for the YICS system is available from PNM in their "set". But since you already have the XJ head plugged, just keep it plugged! Don't use the YICS system, since you essentially have a 79 engine anyways.

So....use the XJ engine and cylinders, get them bored, put the new pistons and all in it, and THEN, when you're ready for the swap, pull the XJ head off of your 78, and put it with the 78 cams onto your XJ engine! Don't bother with the YICS system! This way you CAN keep riding until you're ready to do the engine swap!
T.C.

[excess11]

What???

I know that cranks are spin balanced and that you can balance the rods and pistons so they all weigh the same. But I have never heard of balancing the crank to the weight of the rods and pistons. Our bikes have a 4 cylinder engine so the effect that you are talking about is canceled out by the other cylinders. That is why the firing order is not 1 2 3 4. Your theory would only apply to a single cylinder engine. Where you have to balance the reciprocating mass.

[trbig]

Hmmmm... and the discussion deepens! Thank you everyone.. I do appreciate this input so far. I realize now that the blocks and cranks are essentially the same for both motors... and that the thing that made them different (Pistons mainly) is what's being changed. After GNEPIC's reply, I had really decided not to have the crank done, simply because I am after a cruising bike... with a little extra power to pass when I want it. The extra vibration would be a serious deterent for me since they vibrate pretty well on their own without extra help. Now Excess11 has got me thinking again. On Monday, I am going to call one of the techs at Ape Racing and get their input on this discussion since I don't have the knowledge myself about this. I may take their reply on this with a grain of salt though since they surely would tell a guy what he wanted to hear for some business?? Hopefully it won't be like that.

OK All.... carry on!

Tod

[excess11]

Reply!!!

If the vibration theory was true then how would a big bore kit ever work? The additional weight of the larger pistons would make the engine vibrate like crazy!!! But it doesn't. No one has ever had their crank rebalanced after a big bore kit to make up for this difference. You have one piston going up when one is going down so the additional weight cancels it's self out. The theory has been busted!!!!!