Valve Clearance Advice

0-8er · Oct 4, 2014

Since I had to address a starter problem, I did a valve clearance check today while the bike is in pieces. This is the first valve clearance check and the bike has 30,568 miles on it. All the intake valves are mid range but all my exhaust valves are at the wide edge of the spec range. Here are the values:

Clearance in mm

1 Ex 1 Ex 2 Ex 2 Ex 3 Ex 3 Ex 4 Ex 4 Ex spec low spec hi

0.254 0.254 0.254 0.254 0.254 0.254 0.254 0.254 0.18 0.25

1 Int 1 Int 2 Int 2 Int 3 Int 3 Int 4 Int 4 Int spec low spec hi

0.203 0.203 0.178 0.178 0.203 0.203 0.203 0.178 0.15 0.22

The 0.254mm feeler gauge is very tight on six of the exhaust valves. It takes less effort to push the 0.254mm gauge in on two of the exhaust valves, but it is still tight.

All postings I have read regarding valve clearances say the clearances generally get tighter over time. I would like to hear your thoughts on my exhaust valves having a 0.25+ clearance, do you recommend I change shims to bring it back to mid range? Should I leave it "as is" expecting it to get tighter over time? What would cause the clearance to get wider?

MCRIDER007 · Oct 4, 2014

If it was my FJR, I would put it back together and ckeck the clearances again at 80K miles.

Twigg · Oct 4, 2014

Worry less, ride more

Nuttin' causes the valve clearances to get wider. Theoretically, I guess that if they weren't fully closing, or if the end of the valve stem wore down unusually, that could happen. I guess in theory the shims could wear too, but all three of those possibilities are pretty much unheard of.

The valve clearances wear "tighter" because of valve and valve seat wear. The valves, over time, retract further into the cylinder head moving the end of the valve closer to the shim. If they are allowed to wear too tight then the valve doesn't fully close. This is a particular problem with the exhaust valves as the hot gasses can begin to leak through a seat that should be shut, causing a burning of the valve or seat and a whole world of hurt.

garyahouse · Oct 4, 2014

Here's another question: do valve clearances tend to wear at about the same rate throughout the lifespan of the engine, or do they tend to wear less once the engine made it to say 26k... when it's time for the first valve check?

0-8er's bike shows one valve clearance is down to .178 @ 30k miles. Would a guestimate of an approximate predicted wear down to say .158 by 60k miles be valid?

mcatrophy · Oct 4, 2014

garyahouse said:
Here's another question: do valve clearances tend to wear at about the same rate throughout the lifespan of the engine, or do they tend to wear less once the engine made it to say 26k... when it's time for the first valve check?
0-8er's bike shows one valve clearance is down to .178 @ 30k miles. Would a guestimate of an approximate predicted wear down to say .158 by 60k miles be valid?

Surely the specification Yamaha gives allows for any incremental change that might occur between checks? Yamaha have done the required anticipation of change in the clearance values they've come up with, no need to second guess.

Fred W · Oct 4, 2014

A couple of things...

First off, I see based on your reported clearances that you are using inch based feeler gauges (that are also marked in the metric equivalent). The odd number of mm is the give away. .254 mm is .010".

The spec range for the exhausts in inches is .0071" - .0098" and the range of the intakes would be .0059 - .0087. That is because the specs were set with metric gauges and the inch equivalents were calculated. These can be rounded to .007 - .010 for exhausts and .006 - .009 for the intakes

Using the inch gauges is fine for doing the checks with, using them as go / no-go gauges, but when it comes time to actually shim you will want to use a metric gauge set. A metric set can measure to an accuracy of .01mm (plus some interpolation for looseness or tightness). Inch based gauges can measure to .001" accuracy (plus the interpolation). Since .001" is equal to .025 mm, you will have that much (2.5 times) more precision in your measurements. Which will become especially important when calculating new shim values.

The spec range for the valves is the limits that the engine can be left alone at. This means that the designers know that it will be safe for the next 26k miles if it is found in that range today. If it is in spec it is fine. But furthermore, the only real hazard to the engine is in allowing the clearances to get too small, which is what they will do with valve wear over time.

When the valve clearance during use gets to zero (we don't measure hot clearance, but it is assumed to be something less than the cold clearance) the valve will no longer close fully. At that point your cylinders will not seal, you will lose compression and you risk burning valves due to burning mixture passing through the open valve area.

If the clearance is too large you lose valve open duration and lift, but that will only result in a marginal decrease in performance, probably nothing you would even be able to feel. So a slightly too large clearance is not much cause for concern

As twigg says, there are rare occasions where people have found increasing valve clearances due to wear of the valve train components (not the valves or seats) but these are very rare, and none have been reported on any FJR engines that I am aware of. What does get reported (pretty often) is increasing of the exhaust valve clearances due to a buildup of combustion deposits on the exhaust valve faces and seats. If you are one who tends to baby your engine a lot, mostly use low rpm ranges and gentle with the throttle, this may explain why your clearances are so large.

Running the engine hard every once in a while, as it was designed to be, is a good way to keep the carbon deposits low. You can also try one of the various gasoline additives that claim to reduce combustion chamber deposits used on a regular basis.

MCRIDER007 · Oct 4, 2014

garyahouse said:
0-8er's bike shows one valve clearance is down to .178 @ 30k miles. Would a guestimate of an approximate predicted wear down to say .158 by 60k miles be valid?

I don't think so unless the valve clearance was also measured at zero miles and even then its probably safe to assume that the wear down, at least during break in, is going to be faster than after break in.

TravelinLite · Oct 4, 2014

Good info in this thread. Thanks guys.

Pterodactyl · Oct 4, 2014

Fred W said:
A couple of things...
First off, I see based on your reported clearances that you are using inch based feeler gauges (that are also marked in the metric equivalent). The odd number of mm is the give away. .254 mm is .010".

The spec range for the exhausts in inches is .0071" - .0098" and the range of the intakes would be .0059 - .0087. That is because the specs were set with metric gauges and the inch equivalents were calculated. These can be rounded to .007 - .010 for exhausts and .006 - .009 for the intakes

Using the inch gauges is fine for doing the checks with, using them as go / no-go gauges, but when it comes time to actually shim you will want to use a metric gauge set. A metric set can measure to an accuracy of .01mm (plus some interpolation for looseness or tightness). Inch based gauges can measure to .001" accuracy (plus the interpolation). Since .001" is equal to .025 mm, you will have that much (2.5 times) more precision in your measurements. Which will become especially important when calculating new shim values.

The spec range for the valves is the limits that the engine can be left alone at. This means that the designers know that it will be safe for the next 26k miles if it is found in that range today. If it is in spec it is fine. But furthermore, the only real hazard to the engine is in allowing the clearances to get too small, which is what they will do with valve wear over time.

When the valve clearance during use gets to zero (we don't measure hot clearance, but it is assumed to be something less than the cold clearance) the valve will no longer close fully. At that point your cylinders will not seal, you will lose compression and you risk burning valves due to burning mixture passing through the open valve area.

If the clearance is too large you lose valve open duration and lift, but that will only result in a marginal decrease in performance, probably nothing you would even be able to feel. So a slightly too large clearance is not much cause for concern

As twigg says, there are rare occasions where people have found increasing valve clearances due to wear of the valve train components (not the valves or seats) but these are very rare, and none have been reported on any FJR engines that I am aware of. What does get reported (pretty often) is increasing of the exhaust valve clearances due to a buildup of combustion deposits on the exhaust valve faces and seats. If you are one who tends to baby your engine a lot, mostly use low rpm ranges and gentle with the throttle, this may explain why your clearances are so large.

Running the engine hard every once in a while, as it was designed to be, is a good way to keep the carbon deposits low. You can also try one of the various gasoline additives that claim to reduce combustion chamber deposits used on a regular basis.

Thank you for this.

0-8er · Oct 4, 2014

Thanks for the input and valuable information. I'll leave the shims "as is" and take a look next time.

QUOTE (Fred W @ 04 October 2014 - 6:20 AM)

Fred W said:
First off, I see based on your reported clearances that you are using inch based feeler gauges (that are also marked in the metric equivalent). The odd number of mm is the give away. .254 mm is .010".

You are right about the inch based feeler gauges. I called around town looking for a metric feeler gauge set last night and couldn't find one after hours. Have one on order and it will be here Tuesday.

Fred W said:
Running the engine hard every once in a while, as it was designed to be, is a good way to keep the carbon deposits low.

That is advice I started using as soon as the bike was broke in. Five minutes after leaving work at the end of a long day I can be carving the foothills and ending the trip on one long, straight, smooth, deserted road.

0-8er · Oct 4, 2014

QUOTE (garyahouse @ 04 October 2014 - 5:30 AM)

garyahouse said:
0-8er's bike shows one valve clearance is down to .178 @ 30k miles. Would a guestimate of an approximate predicted wear down to say .158 by 60k miles be valid?

I should have mentioned that for the smaller intake valve clearances, the 0.178 feeler gauge was very easy to insert while the 0.203 would not go in. That tells me the clearances are closer to 0.203 than 0.178.

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