My custom project so far, almost one year in.

Hey all,

I was wondering if a maladjusted valve clearance could cause a motor to barely run. The motor won't run without throttle even then super rough; it is also spitting gas from the carburetor intake (compressing before the valve closes?).

Is this a timing issue? Damaged or stuck valves? I'd like to discuss all possibilities before tearing the head off. I won't be able to do a leak down test until next week.

I've almost completely rebuilt the carburetors and the floats are not malfunctioning, they are squeaky clean.

I've also been setting the valves in neutral, turning the engine through the nut on the rotor, I feel like this isn't giving me the most accurate TDC. Could this be an issue?

Thanks for reading!
 
What's changed since you rode it in that video a couple months ago? It seemed to be running well then. Go for the easy stuff first. Your valve clearance would have to be pretty far off to seriously affect the running of the bike the way you're describing it. Keep in mind the cam lobe profile -- you actually have a pretty broad arc around TDC where the valve clearances should stay the same.
 
As for what changed, I was trying to trace this problem through the carbs and spark first, I replaced a messed up carburetor body and replaced the coils/leads/caps. Those are functioning properly. I think part of the problem was due to bad gasoline, since then I've been using a temporary fuel source made out of a bottle. Could the bad gas have gummed up the valves? There was no defining moment when things went south. I noticed a small power loss at idle. I tore the carbs to clean, and adjusted the valves (most likely wrong). I doubt it's piston related. I plan on throwing the bike in first gear, and using a straw to find TDC....see where it goes from there.
 
Hey Twins,
The straw will work, using the mark's,too. You could have a tight intake that will cause it to back through the carb's. Also, be absolutely sure that the advance rod & weight's are free & not sticking . Very common for that system to bind up, esp. after sitting. I know you run it every once in a while, but when on the road the advance system is in constant movement. So the system will stay free. Dis assembly & cleaning, lubing should help.
Valve adjustment is a relatively straight forward procedure. If you have a hard time defining what a proper clearance 'feel' like, set a hand micrometer to .005 and take a .005 feeler gauge and pull the feeler gauge through the micrometer. It will have a good felling of 'tug', but slide through pretty easy.As cool touch stated, there is allot of cam lobe to get the valves adjusted well.
If the advance rod sticks in the full advance position, that will also cause it to back fire through the carb's. A bad (shudder) valve could also do that. Compression test & cyl. leak-down test will reveal any of those problems.
 
Again, thanks cooltouch and gordon,

Do TCI 650's use an advance rod? I left my manual at the garage. I've been setting the the tappets to .003 and .006 according to XSjohn. Should I return to the original specs in the Clymer (Intake .0024)? My compressor is broken and I'm waiting for my buddy to get out of the hospital to use his for a leak down test.
 
gggGary said:
A bit looser like .003" and .006" is fine. Have you done a compression test?
Click to expand...

The side that is firing right is around 115psi (throttle closed), the problematic left cylinder only gets around 20 or so:wtf:. Could this possibly be incorrectly adjusted tappets? Or more like a stuck valve?

gggGary said:
Resetting a sticky valve could throw things in a handbasket
Click to expand...

So you're saying I'm better off just taking the top off and seeing whats wrong, rather than trying to f*** with it?:banghead:
 
My #1 first thing to look for with sudden low compression is a chunk of carbon on a valve seat. Seems like we have been around this a bit before? trying to set clearance on a stuck valve or one with carbon on the seat can get the clearance way off. From the carb blowing gas comment I would tend to concentrate on the intake valve on the dead jug. Maybe try loosening the clearance some more? Did we discuss blowing air in the plug hole to see where it comes out?
 
gggGary said:
My #1 first thing to look for with sudden low compression is a chunk of carbon on a valve seat. Seems like we have been around this a bit before? trying to set clearance on a stuck valve or one with carbon on the seat can get the clearance way off. From the carb blowing gas comment I would tend to concentrate on the intake valve on the dead jug. Maybe try loosening the clearance some more? Did we discuss blowing air in the plug hole to see where it comes out?
Click to expand...

Do you have a suggestion of a clearance to try on the left intake valve? I'm probably going to try it one more time before I get a chance to do the leak down (which you talked about in another thread).
 
No sorry I don't. I would hate to tell you something that would cluck the motor up worse than it is already.
 
-Okay, well I ended up dropping the engine and taking a crack at a top end rebuild. I'm probably going to keep to stock specifications, unless there is a heavy persuasion to do otherwise. I'm basically planning to install some SS valves, replace the cam chain guide, and replace the piston rings. Everything else should be working fine, but we'll see.
-This is my first time doing this for my 650, so is there anything I need to know before I dive in? Any tools I should look into? Can someone explain oversized pistons/rings/valve guides? When do I have to consider these? :confused:

Also, is there anyway to break the cam chain without damaging it and without a special tool? Bicycle chain breaker?

Thanks again xs650.com,

Twins
 
Twins, you can remove the cam from the chain without breaking it by working the cam bearings loose from their placements. But if you want to replace it without opening up the bottom, you will have to break it or remove a link. MikesXS has tools for this.

You may not need SS valves. Best to inspect the stock ones first and see if they've still got enough meat on them, which they probably will. You may need valve guides though. And you'll want to mic your pistons and your bores to see if they're still within spec.

All this info is in your Clymer's manual, so you should probably give it a read through before you start in on this.
 
cooltouch, thanks for the advice as always.

I plan on reviewing a lot before I start; I'm just a bit anxious and excited to start but it's been hard to get time to work and look at the damn thing. Damn it's busy this time of year.

I've also put off lining my tank, even though I have the POR kit lol.:doh:
 
Hey Twins,
Your valves are probably in good shape. The exhaust might be a little rougher than the intake's, but that is an easy step for a machine shop. They would 're-face' them, grind a clean surface where they seat on the head. They would also cut the seats in the head for all 'new' surfaces. Hence, a valve job.
The thing on 'over' size piston's & ring's is if the cylinder has excess wear, then the cylinder get's a new surface via a machine shop. These are simple operation's- for a machinist. The reason machine shops are costly is the equipment needed to do these job's correctly. They are not cheap.
So, if an engine's cylinder's need to be bored out, depending on the amount of damage, will determine how much metal has to be removed to make them correct. A good machinest will measure them up & inform you what size part's you will need. So, let's say you have a 4" bore, and the cylinder need's to be bored out .050" to make it work-able. That would mean you will have to get .050 larger pistons & ring's.
I don't know what your engine has for milage, but on mine with 10,000 on the clock, my cylinder's are in great shape. When you pull your's apart, BEFORE you pull the cylinder's off the piston's, give them a very close inspection, looking for obvious sign's of wear. Places where the ring's are not hitting the cylinder's. Scuffing of the piston's on the cylinder's,ect. Or a hole in the piston. If that is the case, a complete top end rebuild is needed. But before you order piston's and ring's, you will need a machine shop to measure it up for you. BTW, stainless valves are not nessisarily going to be a whole lot better than stock.
 
To me, the main reason for having a valve job done is to have a 3-angle (or more) grind put on the seats. This improves flow through the head. But if you don't feel you need a 3-angle grind, you might be surprised how quickly you can get a good seal between valve and seat with just a few dabs of lapping compound and one of those suction cup tools. If the seating faces are still in reasonably good shape with a minimal amount of grooving to the valve's sealing edges, it probably will take only a couple of minutes per valve to lap it such that it will have a perfect seal. You can buy one of these tools and a tube of lapping compound for less than $10.

To me, a basic part of my personal set of tools is a selection of accurate precision measurement tools. I own a couple of dial calipers, a couple of vernier calipers, a bottom micrometer, a couple of 0-1" micrometers, a dial indicator, a set of telescoping bore gauges, an inside and outside caliper, and a few sets of feeler gauges. I took a year-long class in hand ad CNC lathe and milling machine operation, so I tend to collect more precision measurement tools than might be strictly necessary, but they do come in handy.

Still, I believe that any serious hobbyist who does his own engine work, be it motorcyclical or automotive, should have at least one accurate (not necessarily expensive, but accurate) set of dial or digital calipers (0-6" is most useful), a set of telescoping gauges, and a complete set of feeler gauges. All the rest are gravy. With these three measurement instruments you can accurately mic your pistons and bores, as well as thickness or gaps of any critical components.

So it would not really be necessary to cart your engine parts down to a machinist if you have your own precision measurement instruments, but when in doubt, it certainly won't hurt to have a second opinion.
 
Thanks for the piston advice/info Gordon, clears a few things up. How's your skull feeling? I'm hoping that the pistons and cylinders are not the source of my low compression and plan on keeping those stock.

Cooltouch, good point about the valve lapping. As for the grinding the seats, I've got no experience doing this nor do I have the tools/gauges for that process. I'm hoping that the valves prove problematic (low compression) and not the valve seats themselves.

I'm a flea market rat, I'm usually end up with about 5 new tools a week. I'll keep my eye out on measurement tools, as I've only got a few basic ones.

More questions:

Is there a specific way to refit the camshaft so the timing isn't f****d?

Are valve guide replacements pretty straight forward? Or is there something to keep in mind there?

Stupid questions but my manual instructions are vague...
 
Twin's,
The head is much better, thanks. Big ol' scar though. Looks like a third eye. The cam timing is important, and easy enough. There is a notch in the center of the cam near where the gear is pressed on to it. That goes to the left side straight up, with a line on the cam gear that line's up even with the head surface at the back of the head.
Guide replacement is a critical job. They have to be pushed into the head perfectly straight. It can be done with a hammer and the tool from Mikes. The trick is to warm the head up in an oven to about 125-150 degree's. The drawback is that they need to be reamed out to fit the valve stem, & the reamer is not cheap. It's like $80. You can buy all the measuring shit if you want, but a machinist who knows what he is doing is actually cheaper. An accurate 6" caliper & a 1" micrometer is all you really need.
 

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