Cylinder compression bad?

[tinman905]

Im already getting "the bug". The wife is already convinced to get a bike shed (we dont have a garage and HER bike needs a cozy home). Dont think I havent already looked for a "parts bike".

The first step to recovery is admitting you need more bikes.

There is no recovery after the "BUG" .If you are not careful you will become a "XS1100 JUNKY" Which I believe is a good thing.

[foreda]

Compression Test

Compression test is, pull all 4 plugs out, put compression gage into one cylinder and test, crank the engine around 4-6 times the needle will stop moving. Note the pressure. repeat for the other three.

Next, if one is really low as stated, put about two teaspoons of regular motor oil in the cylinder, put the compression gage back on that cylinder, retest. If the pressure goes up, you have rings not sealing, if not, you have have valves not sealing.

If it is a valve issue, first step is reshim the valves. Check the service manual for how. If it is rings, follow the info on MMO to free them up.

If it were me, I'd focus on the compression and get that resolved before you go digging into carbs and such. The biggest thing to watch out for on the carbs is the float post. If the pins are even slightly stuck, I'd make the tool Ken has posted before. I made on form a piece of aluminum angle stock. Best time and money I ever spent! I am sure it saved me a few broken post on the last set of carbs I worked on.

When you have it ready to ride, pause a moment and look in the manual and do ALL of the service items listed.

Don't forget to open the throttle wfo while checking compression.

[James England]

Without a clearly thought out diagnosis, you'll spend some money and maybe, if you're lucky, fix it by accident...I'm not being derogatory here. You've mentioned low compression on one cylinder and the fact that the engine is rough at low revs. There's no linkage between the two, because you also mentioned the possibility of a gaping hole in one of the inlet manifolds, correct? And it's stood for a year....probably with fuel evaporating out of the carbs .

It seems to me that this compression thing might be a blind alley. You've passed it on because the mechanic mentioned it, but he may have got it wrong.

You see, I would do the opposite of previous postings and start by looking at the carbs first.... certainly obvious things like inlet manifolds and so on. Sorting out the compression is a more major job, IMO, than doing the carbs. You're talking camshafts out, head off, gasket renewal, torque setting on head bolts, maybe a rebore etc.... whereas your misfire and rough running could be something simple in the carbs or manifolds. Popping and banging is unlikely to be compression or lack of. It's more a sign of carburation.

As I said before, I've never checked the compression on any of the four XS1100's I've had. I can't see the point if it runs OK. And if it doesn't run OK, I'd start looking at the obvious and easiest first... spark plugs, carbs, coils. The last thing I'd be doing is taking the cylinder head off, renewing rings, rebore, new pistons etc. You'll spend more money on a cylinder head gasket that what it would cost just to have a look at the carbs etc first. You might find a pinhole or tear in a carb diaphragm... a dodgy float valve.... simple, easily identifiable problems.

If, after having a look for the cheaply rectified and obvious, you still get nowhere, then yes, think of head off and valves and rebores etc etc but not right now... imagine doing all the head off stuff and then finding it still runs rough... because of a $20 inlet diaphragm...

[Redshirt]

Thanks for the procedure and tips. I will be following them.

So I just got back from the mechanic with my bike...
After talking to him he indicated in more detail what he did and conclusions he came to.

He performed the compression test with the following results: 140-80-140-140.
He then put in some lube (i forgot what type already) and tried it again:
Results 140-90-140-140.

He told me that he is pretty sure its the ring, but he was trying to spare me the expense of all the labor it would cost to work on it. Our initial conversation left him with the idea that I had no money to put into the bike. Thus his reluctance to do anything else that would cost me. In hind sight, it was a nice gesture.

The Ride Home™ "the experience"
Cold start+no enrichment (choke)+low battery = jump and choke open to get it going.
Vapor from left pipe (2nd cyl. side I suppose). Right pipe no vapor.

Rode the bike home from the shop (where I had brought it in on a trailer). Under 3k rpm, the engine struggles. Sputtering and underpowered as though it was out of gas, it requires a great deal of throttle to get it beyond that barrier. Once 3k rpm is hit, it opens up and has power. Took it up to about 55, cycled through as many gears as traffic allowed, almost got plowed by a merging bus. It has giddy-up (thanks, bus), but still feels underpowered (understandably).

Keeping the throttle steady, at about 45 mph, I felt a subtle variation of speed.

Epilogue
Parked at my house, a gasoline smell was heavy. The brake rotors looked much shinier and clean but the rear rotor was very hot. Front rotors were warm. I do not ride the brakes and have heard of some brake issues. Brake caliper rebuild may be in the list "to do".

Otherwise, I was happy to get on it and ride a little. Love the sound of the engine.

James, Thank you for your thoughts. I will likely go that route. Carbs, boots, coils, plugs. I wanted to give it all attention anyhow for peace of mind.

[CatatonicBug]

Once 3k rpm is hit, it opens up and has power.

That sounds like carbs to me. The pilot jets feed fuel until that point, then the main jets kick in. You probably have some clogged pilot jets, along with a bit of fuel residue throughout the carbs. Clean 'em really good, and re-install, and I bet you'll feel a LOT more power.

[natemoen]

I agree, clean the carbs and put some miles on it and see what compression is like after a couple hundred miles.

[motoman]

A +1 , then some to what England stated! You pull that carb bank off(do NOT seperate), remove float bowels and blast some carb cleaner through all open orfices you find, fix the intake boot problem, you'll see some definite improvement. As England stated, if your interested in learning/fixing issues yourself with some help here and maybe someone close familar with mechanical bike issues, it can be fun and at times challanging sorting out ANY older bike issue. There have been several here who with no real mechanical ability, but interested in learning how to make the necessary repairs now have an excellent running scoot, the knowledge they didn't have prior..........and a smile that can't be wiped off. The shop mechanic initially used may or may not have the ability........more times than not have seen this situation here with a new owner having a shop "mechanic" work on there bike and several hundred and even a thousand dollars later not properly fixed and no improvement.....just a warning from the wise as others here will concure.

[James England]

If you decide to take the carbs apart, check this forum very carefully. There are loads of really good posts about how to do it. It may appear daunting but it isn't... it's the same thing four times over. Use correctly sized screwdrivers to get the slotted jets out...they need to be a very good fit and then apply plenty of pressure when you turn the jet, to get it loosened. You don't want the screwdriver to 'ride up' over the edge of the slot in the jet because it will round it off, so a correct screwdriver and holding it down with good pressure is vital. I once had one slip and render the slot useless... I ended up drilling it out with ever increasing sized bits until what was left started turning when I used a screwdriver pushed on it.... big relief.

Remove the float pivots with wire snippers to get them loosened without putting sideways force on the two posts that they pivot on.

By the way... I replaced my intake boots because they were badly cracked externally. Three of the four were fine inside though (they are double skinned).

Personally, I think it sounds pretty hopeful! At least the engine fires and runs, however badly. That's a big positive.

Re brake discs... they get pretty hot just stopping outside your house.... If you jack the front end of the bike up and spin the front wheel, and spin the rear wheel, you'll soon know if they are binding......

If you get it to run reasonably smoothly, I'd use it for a few months and forget the compression thing for now... see what develops

[crazy steve]

He performed the compression test with the following results: 140-80-140-140.
He then put in some lube (i forgot what type already) and tried it again:
Results 140-90-140-140.

He told me that he is pretty sure its the ring, but he was trying to spare me the expense of all the labor it would cost to work on it..

It might be the rings; but that's not much of an increase after oiling. I'll be contrary here and recommend checking valve clearance first. If you've got a tight valve causing the low compression, continuing riding it without addressing that will burn the valve and maybe the seat, and then you will be pulling the head. If after making sure the valve lash is good, if compression still doesn't come up then go ahead and ride it and see if compression improves.

The numbers on the three are good by the way...

[DGXSER]

Here is the flip side to James' recommendation. IF there is a compression issue as it appears to be. Then the pump is not going to work right no matter how clean you get those carbs and how perfect and tight the intake boots are or anythign else you clean and make nice. It will still run like crap on that cylinder. Which may leave you to think you have not got something else right, carbs not clean enough...boots not tight enoough... and chase parts for months on end. Depending, it may well pop and backfire form the bad compression. Fuel can build up from not getting compressed to burn until it detonates like a diesel.

The numbers posted on the compression lean strongly to a valve issue. As it is even cheaper than carb work, or boots, or the other stuff, and not all that difficult, I'd start with checking the valve clearances and re-shim them. Then recheck compression.

Moving on to the other stuff and not addressing the compression to the point of knowing what the cause is, is like ignoring it. And as a fellow XSive puts it, the only problem he ever had that went away by ignoring it was his Ex-wife!!

Anyway, which ever direction you take, have fun, and ask questions before you make the next move if your confused. Easier to ask and learn than to fix what broke cause you did not ask first.

And before you ride that beast again, do please give the entire brake system a thorough cleaning. Typically you do not even need new parts, just clean the old ones and re-use. So it only cost you time and some brake fluid. Putting the GO before the Whoa can cost you some bones....the ones in your body, not your wallet.

[Redshirt]

boy have I got a lot to learn.

Ok Im hearing multiple things that need to be addressed and valves and shims are now added to the list.
Im looking through the manual for reference to valve lash and I dont see anything. Is this a colloquial term? What does it represent?

I see specs for valves:
Intake
Stem clearance (cold) 0.0004-0.0016in.
Exhaust
0.0010-0.014in.
Stem runnout max 0.0012in.
Valve seat width
spec: 0.043 in.
wear limit: 0.080in.
Valve clearance: 0.21-0.24 in. exhaust, 0.16-0.20 intake

Then I see the calculation for measured clearance, specified clearance, excessive clearance.

Are valve shims sometimes refered to as valve pads? It seems to be but if I dont ask, my head will explode.

To measure the clearances, will I need to buy one of those "swiss army" bladed gauges? What about a Valve Adjustment tool? Any other tools?
I plan on getting a compression gauge.

[CatatonicBug]

And before you ride that beast again, do please give the entire brake system a thorough cleaning. Typically you do not even need new parts, just clean the old ones and re-use. So it only cost you time and some brake fluid. Putting the GO before the Whoa can cost you some bones....the ones in your body, not your wallet.

VERY good point!! Even bikes that are used regularly need to have the brakes cleaned out every year or two. If that one has sat a while, I bet the fluid looks like cola! Or worse...

[crazy steve]

Valve clearance: 0.21-0.24 in. exhaust, 0.16-0.20 intake

Then I see the calculation for measured clearance, specified clearance, excessive clearance.

Are valve shims sometimes refered to as valve pads? It seems to be but if I dont ask, my head will explode.

To measure the clearances, will I need to buy one of those "swiss army" bladed gauges? What about a Valve Adjustment tool? Any other tools?
I plan on getting a compression gauge.

Valve clearance, valve lash; same thing. Yes, to just check the clearance, you'll need a set of feeler guages ('bladed' things). If you actually need to change the lash, you'll have to remove/replace shims (I've never heard them called 'pads', but maybe) and you'll need a tool for that. Do a search for 'valve adjustment tool' and you'll get all sorts of results. Motion Pro makes one (which has gotten uneven reviews as to functionality), some guys make their own, some pull the cam caps loose. Lots of reading...

[CatatonicBug]

There's a guy on ebay who sells those valve tools. He usually has only one available at a time, but as soon as one sells, he puts up another one. Not too pricey, but I've never used one, so I can't vouch for the usability.

[DGXSER]

Like Steve stated, the clearance is what your looking to measure. As to the tool. I did it once using the tool and it worked reasonable well once you got the hang of how to set it up. But, the cam caps method is pretty simple. As long as you have a torque wrench, that would be my choice.

Get the compression gage and check it for yourself. With the same results, pull the valve cover off. look around in there a few minutes or so, take pics and then read some of the threads on here about re-shimming valves by loosening cams and ask questions as needed.