Intermittent Performance

[TedMosher]

Hey all,

First post to the forums, I've got a 1980 xs1100SG. I've had it for 3 years, the bike is in rough shape. I've put about 8000 miles on it, and really am just now starting to put some TLC into it.

My issue is the bike has trouble starting, it doesn't like running for more than a few minutes at a time, and the cylinder on the far right (when sitting on the bike) is pushing at about 45PSI with the other three around 75PSI. I took the valve cover off today and found the intake side clearance to be in-spec, but the exhaust to be quite tight (between .13mm and .18mm)

I've cleaned every electrical connection on the bike, and just recently installed a new generator. In trying to chase down this issue.

I read that a compression test pumps 145 PSI when the bike is new. Do I need new rings? Is rebuilding this engine something I can do myself for under $250? If so, how many hours would you guess it'd take for someone who has never rebuilt and engine before?

Thanks for reading!

-Ted

[b.walker5]

Hi Ted.

Your compression readings seem way too low and could indicate significant problems, and would most certainly give you starting and idling problems. First thing I would ask is exactly how did you perform the test?

There are two schools of thought about whether the engine should be warm or cold, but either way the basic principle is the same. Clean around the plugs with an air gun and take them out. Disable the ignition by removing the primary wires to the coils. Jam the throttle wide open and crank the engine over a few times. Take your first set of readings from 1 to 4 and record them. Allow the engine to crank 3 or 4 times to get a good reading. For your next set of readings, using an oil can, give 2 or 3 good squirts of oil into each plug hole just before testing. As before, crank 3 or 4 times at least to get the best reading. Note the readings and compare each cylinder. No increase with the oil indicates an upper cylinder leak, i.e. gasket or valves. An increased reading indicates worn rings (the oil provides an extra seal and will increase cylinder pressure)

With a good manual (see Catatonic Bugs weblink) and a little 'nouse almost anybody could rebuild one of these, but I think your $250 budget could be a little optimistic.

[DGXSER]

Brian has you covered on the compression test. That and a good leak down test will tell you what is causing your problem. BTW, if you did not hold the throttle full open during your compression test those numbers you have are quite possible on a good engine.

The gasket set alone is $100, and you will need one, no doubt about it. Then there is rings, 1st overs will cost you easily $100 typically (you might get lucky and find a set on fleabay cheap.) You may want to have a machine shop hone the cylinders. You will want a fresh cam chain for another $50 time you get the chain, the link and the tools. I'd say if you got the engine complete for $250 you probably missed something.

Another option is to keep an eye out for a used engine.

One more thing, when you get an engine with good compression in there. Go gentle on the throttle at first, cause you have no idea yet what power this thing will have!!

[crazy steve]

I'll expand on what Don and Brian said a bit...

Keep in mind that 'rebuilding' the engine will consist pretty much of only replacing the rings, and maybe the valves. Pistons (in any oversize) have been discontinued for years, as are crank/rod bearings, and are difficult/expensive to find. The one exception to this is you can still get a 'big-bore' kit from Wiseco, but the kit is $500+ and will require a rebore (another $100+), so you're well beyond your budget. Even rings are hard to find; I think you can still get those from Yamaha, but they're $50 per hole. Most guys are using aftermarket oversize ring sets (sometimes found on eBay for $40-50) and filing them down to fit. This assumes your pistons/bores are still within wear specs.

Same thing goes for valves; new reproductions are available (from Oregon Motorcycle Parts), but are $120 per set of intakes or exhaust.

If you're on a budget, it's usually far cheaper to find a good used motor, or even a good top-end (barrels/pistons/head) and replace rather than repair...

[TedMosher]

Compression Test

Bad news is I did do the oil in the cylinder test. It brought the far three up to 100 - 125, and the 4th up to 75. Good news is I never touched the throttle for any of the tests. They were all done cold, and I cranked the engine with the starter.

I'll test again with the throttle, and report back.

[TedMosher]

Good news I think...

Compression test done cold, throttle wide open, all spark plugs out, no oil added.

From right to left (while sitting on the bike) I got 155PSI, 140PSI, 130PSI, 135PSI

Also as no one responded I was wondering what the tight exhaust valve indicated if anything?

What's next Guru's? I'm mechanically inclined but have limited experience with this sort of thing. Thanks so much for your help so far!

[DiverRay]

First thing is to ADJUST ALL VALVES! the pads have numbers on the bottom side, and tell you how thick they are supposed to be. I use a 0 to 1 micrometer to measure the actual thickness of the pads. The manual that you downloaded from "Bug" has a chart that should help in choosing the proper size pad to put in. Figure on all day the first time around, and be VERY CAREFUL with the cams when doing the adjustment. This will also be a good time to adjust the cam chain. YOU MUST FOLLOW DIRECTIONS! YOU CAN KILL THE ENGINE IF YOU DO THIS WRONG!
Once you have the valves properly set, you can then check the spark plug caps for resistance. Use a VOM to make sure all 4 are the same, about 5K Ohms. The caps just unscrew off the wires, so it's easy to check or change them.
Next is check the timing with a light. It usually does NOT need adjustment, but if you don't know what the PO has done, it's a good idea. The bike should be running well after that!
Don't forget to do a search on carbs as well. You could have some dirt in the carbs, and be in need of cleaning. Seafoam is an additive you can buy at O'Rilley's, and MAY fix or help with the carb problems.
Welcome to the site!

[crazy steve]

..Also as no one responded I was wondering what the tight exhaust valve indicated if anything?

That simply indicates that the valves haven't been adjusted in a while...

Remember, valve clearances get smaller with wear on these, not larger. That's why it's so important to keep them adjusted; too tight, and you risk burning them.

[TedMosher]

There's yur problem...



Well that was at least some of the problem. Now I need some shims for the exhaust side. Can anyone suggest a good source/idea for getting valve shims?

[DGXSER]

After you finish the cleaning process, try a local bike shop for the shims. They are 29 mm in diameter. And no the 29.5 mm ones will not work. I and several others found they will sell them to you pretty cheap.

[natemoen]

Talk to Davinci here, he will trade shims with you if he has the right sizes (which he usually does).

[TedMosher]

Seems pretty good...

So today I became abit discouraged because I'm flying from New Mexico to be in New England for a couple of months on June 9th. There is simply no way I could order the valve tool, determine and order new shims, fit them and seal up the head before I'm leaving for awhile. So I put the valve cover back on and made sure the old gasket sealed at least adequately. Put the new cleaned carbs in and started it up. Beautiful Idle, woah I thought...I buttoned up the rest of the small stuff, put the seat on and took her for a short spin. The bike ran beautifully. I was so pleased, I'll still certainly adjust the valves when I return, but boy was it nice to know my precious xs11 was still alive and well.

However the bike doesn't seem to be charging the battery, so...I was wondering...where do I start?

Thanks so much for your help thus far guys, I'd be stumped without your experience and participation.

Now to determine why the battery isn't charging...

[sabar10]

drivability issues.

Compression test done cold, throttle wide open, all spark plugs out, no oil added.

From right to left (while sitting on the bike) I got 155PSI, 140PSI, 130PSI, 135PSI

Also as no one responded I was wondering what the tight exhaust valve indicated if anything?

What's next Guru's? I'm mechanically inclined but have limited experience with this sort of thing. Thanks so much for your help so far!

looking at these compression readings on a cold engine with no oil i would say you have enough compression for this unit to run, however tight valves on at least the 130 psi cylinder may be possible but one cannot rule out carb issues after seeing the pics posted. i have had my xs for 32 years bought it new in 79, the advancer unit on the left side has wires that over time will shear from time and movement and this will cause a number of concerns. one other thing that is also a concern is how long did this engine sit? Rust never sleeps.

[bikerphil]

However the bike doesn't seem to be charging the battery, so...I was wondering...where do I start?

It won't really be charging at idle, gotta rev it up a bit. It should be 13+ volts at 2500 RPM and 14+ volts at 4000 RPM at the battery. If it is any lower than these readings, first place I would check is the alternator wire connector located in back of the fuse panel. It has 3 white wires and that connector can melt or corrode and hinder the charging.

[natemoen]

For the charging, first thing to do it to actually measure the voltage of the resting battery (should be about 12ish), then start the bike and measure voltage again (hopefully still about 12ish), then rev the engine to about 3500and check the voltage again (should be 14ish). If the first 2 are low then you need to charge the batter or may have a bad battery. if the last one is pretty much at the same as the second measure then I would first say to check the large white connector behind the fuse panel, it gets dirty and melts, 97% of the time that is the problem.