Planning 1980 xs1100 big bore project

[trbig]

trbig,


I didn't catch if you have done a big bore and ridden one?

Mine is the 1179, but I built another persons bike using the 1196 and rode many miles on it before and after the bore, as well as rode another's that I helped with another 1196. Two of them are XJ's and the other was one of the earlier 78/79 models. None of them had any noticeable change except a fresher/tighter motor. You will be FAR more money ahead if you can find a good stock exhaust, which these bikes were tuned for, as well as a set of really well tuned carbs. Sure, a good find on a good exhaust will set you back several hundred, but it's still cheaper than a rebuild. When I crashed my 81 Special and had to mount aftermarket mufflers, the HP loss was/is VERY noticeable. The HP I lost on my XJ when I went from a stock exhaust to a Special exhaust was very noticeable. Heck.. Accel coils will boost your HP more than a big bore. I realize nothing beats CC's, but I can honestly say that the only HP gains you're going to feel are the difference between an old tired motor and a fresh one with higher compression.

[TopCatGr58]

Hey Steve,

After I did my "little" 1179 big bore and got it broken in, I put it on a Dyno, and didn't see much of an increase in HP or torque compared to IIRC a fellow with a well tuned stock Xsive?? But I've got the 81 engine with the electronic advance curve. Your thoughts about the increased initial timing has me a little intrigued. I know I can take the timing plate off and slot the unslotted sections to allow me to advance the intitial static timing. I'm only getting the ~30 mpg as well, and I think I remember someone saying that they could smell a bit of fuel riding behind me.

I think I remember loosing a bit of the low rpm grunt when I put the 4-1 pipes on my stock machine back in the early 80's....(yeah, call me young/dumb back then), but I also think my pipes got damaged in a wreck, and thought the 4-1's would give me better flow/performance. It did move my powerband up a bit, and my engine does enjoy running in the upper rpm range.

Now that I'm running the modified velocity stack type filter mounts, plus the Dynatek coils, my bike does seem to have gotten some of it's low rpm grunt. But wondering if I might be able to increase the speed at which the engine will wind up if I increase the initial timing by 5 degrees or so?

Hey Tod, well I guess I'll hope to be lucky and see if I can get my engine to go over 100K total(at least 50K on the big bore) before the bottom end decides to go?? However, I've still got some 34K yet to go before I even get to the second 50K total, and with my limited usage, may take a "few" years! But since the big bore doesn't necessarily give one much more increase in HP, then there shouldn't be much more stress on the crank bearings than the stock engine, and since the bearings were already broken in, and working well...and folks have put over 100k on their non modded engines, I don't see why it's really necessary or prudent to have to split the cases and plastigauge the crank if it was otherwise non-symptomatic??

T.C.

[crazy steve]

Hey Steve,

After I did my "little" 1179 big bore and got it broken in, I put it on a Dyno, and didn't see much of an increase in HP or torque compared to IIRC a fellow with a well tuned stock Xsive?? But I've got the 81 engine with the electronic advance curve. Your thoughts about the increased initial timing has me a little intrigued. I know I can take the timing plate off and slot the unslotted sections to allow me to advance the intitial static timing. I'm only getting the ~30 mpg as well, and I think I remember someone saying that they could smell a bit of fuel riding behind me.

I think I remember loosing a bit of the low rpm grunt when I put the 4-1 pipes on my stock machine back in the early 80's....(yeah, call me young/dumb back then), but I also think my pipes got damaged in a wreck, and thought the 4-1's would give me better flow/performance. It did move my powerband up a bit, and my engine does enjoy running in the upper rpm range.

Now that I'm running the modified velocity stack type filter mounts, plus the Dynatek coils, my bike does seem to have gotten some of it's low rpm grunt. But wondering if I might be able to increase the speed at which the engine will wind up if I increase the initial timing by 5 degrees or so?

T.C.

Increasing initial timing will improve low-end grunt, but your problem will be limiting max timing. You can no doubt bump it up some (and using higher octane fuel will be needed) but being unable to limit total timing may cause pinging at high RPM. Possibly worth trying, but try 'sneaking' up on it a few degrees at a time...

[trbig]

Slotted cam gears would also help with timing. I've read several people talk of improvements with a 5 degree advance.

TC, what I was suggesting is if he was going to rebuild the engine and have the cases split anyway, then I suggested replacing the crank bearings. I wouldn't even dream of trying to do a job like this without splitting the cases and having a look at things in there. I don't think you can get the cylinders off the bike without engine removal, and splitting the cases with the engine removed takes less than 30 minutes if you're taking your time and drinking a beer. Every motor I've had apart shows wear and scratches on the crank bearings.. even some motors that are pretty new. Quite a bit of wear on the thrust bearing half that prevents sideways movement of the crank and the end bearings closest to the outside of the cases usually see the most wear. If you think it's a waste of time to take a look at the bearings, it's your call, your engine, and your time and money, but it seems unfathomable in my mind to not even take a look at them while you're spending hundreds and hundreds on a rebuild to make a motor like new?

Maybe I'm a bit jaded because I've had a couple crank bearing incidents. My first motor I had ran SUPERB in the bike and didn't have a single symptom before it spun the outside left crank bearing. This not only ruined the bearing... it ruined the crank and the engine case as well. A really nice running engine was complete junk. If you want an engine to last you 100k miles, that's great, but I'd like one to last 300k miles. I passed that 100k a long time ago I figure. In your case where you might not think YOU personally will ever get there, think of all the terrible PO stories we hear. Might be nice to leave a good one for the next guy, right? lol.


The Rod bearings are the ones I suggested to plastigauge if they had any doubts. Every time I've rebuilt a motor, I've replaced the crank and rod bearings, but every rod bearing I have replaced still looked nearly new. I've never seen any copper exposed yet on the rod bearings... but that doesn't mean you shouldn't at least check them while you're there. A visual is good, and plastigauge is better, but if there's no copper showing, it's going to plastigauge out just fine. I've just changed my mind about automatically replacing them every time.

As I said, it's totally your call, but it makes no sense to me if you're that far into it.

[WMarshy]

If you haven't read this already... the digital ignition system I posted about has several curves to choose from including additional advance at low rpm... Like anything else its just a matter of how much you are willing to spend.

http://www.xs11.com/forum/showthread.php?t=39503

[Bonz]

Thanks trbig, good stuff to share. I have stock exhaust on both my 80G and 80 SG, other than welded some Harley mufflers on the back end of the 80G because the stock muffs were rusted toast. Kept the crossover. Was very deliberate in keeping the crossover, I don't want to take an "easier" way out and lose out on the tuning the stock system brings to the party.

For the advance, I can vouch for a few more degrees of initial advance being very good for throttle response and overall crispness in the low and mid range on a couple of my bikes.

Had a Bandit 1200S, put a +5 degree rotor on from Holeshot Performance and woke that bike right up. You think you have a great running bike and can't imagine it being better, then you add some advance and find out it can be better...

Same with my current ZRX 1200, +4 degree rotor and disconnecting the the throttle position sensor allows max advance to come in sooner, made it a different feeling bike as well. The ZRX has an ignition map based on throttle position and engine speed. Disconnect the TPS and it's solely based on engine speed, which puts the throttle signal to WOT all the time, gives advance based on engine speed. It is a nice increase in "snap", above and beyond what the +4 degree rotor intially gave.

I still could still run regular fuel as well in both those bikes, so I don't think it would be an issue to add 5 degrees to the overall advance with an even lower compression XS motor.

[greengoon3]

Yeah your probably right about the hp gain, restoring the upper end will see some gain if wear is involved.

I am stuck with a kerker exhaust never had the original.

I do have a set of 79 carbs with the steel floats all rebuilt, jetted up and ready to put on if I can find some fuel and overflow tees.

I bought some off of fleabay and they won't fit the older carbs I guess?

I have considered a coil upgrade but unsure exactly what is best at a reasonable bargain.


Thanks for the input!

George

[GLoweVA]

I have considered a coil upgrade but unsure exactly what is best at a reasonable bargain.

George, I'm in the process of doing the Honda VF coil upgrade on my SG, As soon as I get this engine transplanted and the NGK red caps in then I can get her running.

I'll everyone here know how that goes.