Valve shim sensitivity?

I am adjusting my valve shims and don't know how sensitive the clearances are.

Currently my clearances are approximately

Intake: .076 .102 .076 .102
Exhaust: .17 .165 .14 .165

They are supposed to be .11 - .15mm and .16 - .20mm

I have heard that the closer you can get to the lower of the two figures the better and that getting close to the upper end of the spectrum could cause valve train damage.

For example if I go up the next size on the exhaust of cylinder 3 then the clearance will be around .19mm Possibly even a little more since my feeler guages jump around (ie. .038, .051, .063 etc)

I am thinking I only need to change the intakes on 1 and 3 and the exhaust on 3. Right? The biggest reason I am wanting to do this is because there is only one cylinder within spec compression. However from looking at the clearances two of them should be good.

 

Our valves normally slowly tighten with mileage, so setting them at the tight end of spec will only hasten the need to re-adjust the clearance as normal wear progresses. If things really get tight, you will probably have a burned valve and/or a cam-lobe wear issue..

Running at the high end of the clearance spec may cause a bit more valve-gear noise, but will not be any problem.

PS- your intake valves all need the next thinner shim, as does the one tight exhaust valve. This will probably be the only time that your engine will need to have the valve clearances adjusted, so why not do it right?.

 

Awesome, thank-you for the info. It has about 25k on it so we will see just how long I keep it. Just out of curiosity, why is it that they get tighter? Is it because the valve shafts themselves get stretched out?

Also when I was sticking my ziptie into the sparkplug hole to hold the valves open I noticed that they are kinda dirty. With black spots on them. Not just coated black because I could see silver also. Is there a decently easy way to clean them without taking the motor apart?

 

Best way I know to do valve work is with the head off.
You can check valve seating and guide clearance, and check the grind on your valves.

The only time I work on valves with th engine together is when I replace a valve guide seal, spring or keepers. (with compressed air to hold the valve in the closed position)

Sometimes, (really usually) you just can't cut corners and do a good job.

 

As far as the valves getting tighter. That is because the valves actually seat themselves farther into the seat as they were. IE the valve clearance gets closer to the cam causing the need for adjustment. As far as cleaning out the underside of the valves. I would suggest using some seafoam as instructed on the bottle. Use it in the fuel tank and it should clean everything out. This might be better done in the spring though, when you can get out and run the bike.

 

Do a "Wet Compression Test" to determine what's causing the low compression.

Get the compression values across-the-board. Write them down as a base-line.

Re-check each hole after adding a teaspoon of Marvel Mystery Oil.

If the values RISE >and hold < from the base-line. The cause is RINGS, not Valves.
You have to pull the Head and Block, to HONE the holes, and REPLACE the RINGS.

If the values RISE; but rapidly fall-off.
The cause is likely cracked rings or cylinder wall scoring. Repairs depend on the findings when you get the engine down.

If the values show NO CHANGE. The cause is VALVES. You need only to pull the head and service the valves. Lap new gas-tight surfaces on the valve and seat. Replace Oil seals. De-carbon and do any head porting while servicing the valves.

 

Ok, thanx for all the help. I'm gonna adjust my valves and then run some seafoam through it when it gets warmer and check the compression again and go from there. Plus I have put some oil in the cylinders for winter storage so it wouldn't be a good baseline.

Thanx again :mrgreen:

 

what kind of compression #'s are you getting?

 

I can't remember exactly since I did it in the middle of summer, but one of them was around 120 then something like 70 - 90 for the other three. I really don't think its the rings because over the last 2500 miles I have barely had to add any oil and it doesn't visibly burn it.

I don't have any experience with valve clearances but it looks to me like that is the main culprit.

 

Most experienced Mechs know that a top end rebuild requires a bottom end rebuild.. as in rings/ bearings in the least.
Redoing the head on a moderately used engine restores full loadings to the bottom end bits.. but being no longer new or up to specs, the rings and bearings soon fail under the suddenly renewed strain... not good.
Sometimes one can get away with only a top end renew.. but by my and the general accepted experience.. not very bloody often.
Moral is : Don't fix it if it ain't actually Broke... and when you do. ..do a Good job of it.. or face having to a V good job of it again, real soon..

 

Um... I'm not rebuilding the top end. I'm just adjusting the valve clearances.

So you are saying that I can't adjust the valves without completely rebuilding the engine? That doesn't sound right. I don't think that is necesary unless you already have something wrong with the bottom end or it has very high miles.

It would be much more detrimental to the health of my engine if I continued to let it run with the compressions between the cylinders being off as much as they are. Since I don't have the money for a complete rebuild I would just have to keep running it, I would have to take your advice and "don't fix it if it ain't actually broke" and the clearances would get tighter and tighter until I wouldn't be able to get the shims out without removal of the cams and possible have the engine seize on me after destroying the cams.

By the way did you ever find out what seized your motor, for sure?

Thank-you for the heads up, however just incase you are right, I will post an update in this thread to let people know what the outcome was (prob next october or november) after I have been riding it for a while.

P.S. - If anyone else has some hard evidence that this is true, please feel free to chime in, I just find it hard to believe.

 

You can definatly adjust your valves without needing to rebuild your engine.

I'm sure Danilo was refering to rebuilding your top end when it is worn out and not addressing the bottom end.
That is a rule of thumb, nice tight top end will take out the lower end if it's got some moderate to bad wear.

BUT - that doesnt count checking and adjusting valves!
You can do this and it is considered a part of normal periodic maintenance.

Just be careful you dont set those valve tighter than recomended- especially the exhaust valves!
a little loose is considered ok or at least definatly better than too tight.

 

Oh ... I have a good idea that you WILL be overhauling the Top End.
Nobody makes "Magic Shims"!

Adding the required shims to bring those clearances closer to - or - at spec's -- is NOT likely to do anything to restore the low compression numbers; nor increase compression on the holes that had the low compression readings.

The valve clearances you measured did NOT look to be so tight that you'd be suffering compression loss do to tight valves, or excessively tight where you'd have burned valves.

But ... BIG BUTT!

If the bike sat without being jacked-over ... you leave the door open for a couple of issues which WOULD make the valves suspect. Maybe the valves stayed open long enough to corrode the valve face's and seats a little bit.

To get your compression back ... you'll have to pull the head and lap the valves. Minimally.

Shims won't bring-back lost compression.
Shim clearances ONLY serve to PREVENT losing compression.

Don't waste any dough buying shims until you nail down WHAT is causing the low compression.
If you wind-up lapping the valves. You'll probably wind-up close to needing a couple shims -- after you have the valves lapped-in or new surfaces cut during the valve job.

 

Allright guys, thanx for the info. I'll just have to save my pennies and get into the motor more later.

 

Viper,

I just pulled down my parts motor and had several valves so tight that I could not fit my smallest gauge under them!
Compression was OK on this motor and it did not use oil, but I do not think the PO did any maintenance at all (bottom end needs a major overhaul).
I don't think your problem is caused by the shims!