Simple valve check defies manual

[Oliver Boy]

All I want to do is check my valve clearances, should be simple- right?
Bike was running fine most of last season, but poor starting made me decide to take a look at the valves before timing and carbs...
Issue one; when the end of my camshaft is at the position stipulated in my Clymer manual, it states that I should be able to check exhaust valve clearances on cylinders 1 and 3 ; except the lobes on #3 do not align with those on #1.
Is there some other secret manual I should really be taking reference from ?
Issue two ; the smallest feeler guage in my kit is .038mm, and none of my valves has that small of a clearance, even though the minimum tolerance is meant to be .06mm.
I'm stumped; has my 1982 DOHC been substituted with some other engine?

 

[The Jimbonaut]

Hey man, I checked my valve clearances today as well (also using the Clymers as a guide, in fact it's open on the table next to me), and noticed the same thing. The lobes were not aligned. Thing is, I'm not sure they're supposed to be. I could be totally wrong, but at least you can take solace in the fact you're not alone =)

As for the clearances - my gauges are in inches. But I just did a google check and 0.038mm is 0.015". The smallest gauge I have is 0.002" (0.05mm). That happened to be the smallest clearance I found, and from what I've heard a good clearance is 0.005" (0.127mm).

Sorry I can't be more help, but hope someone will clear this up for both of us

- J

 

[Oliver Boy]

Thanks Jimbonaut.
I guess a new set of feeler gauges is first on my list.
I'll do a compression check on all the cylinders too; if they are all OK I may leave well alone.... I'm concerned that if my manual is inaccurate regarding the cam lobe orientation, the clearance figures may be unreliable as well.

 

[The Jimbonaut]

Hey fella,

From what I understand, higher valve clearances would not adversely affect compression, although smaller valve clearances would.

I ran another valve clearance check today - numbers came out pretty much the same as yesterday. All my measurements are in inches, the smallest being 0.002" on a few (not however on #1 cylinder) and the highest being 0.009 (which is the second exhaust valve on #1 cylinder).

The cylinder compression is 150psi on #'s 2, 3 and 4, but 130psi on #1. I poured a teaspoon of engine oil into the spark plug hole in #1, cranked the engine and it jumped to 180+psi. Again, from what I understand, that isindicative of a piston ring problem,and possibly something else which I'm hoping to find out (with help from this forum!)

Good luck man, interested to hear how you get on.

By the way, I think Clymers is correct - use the mark on the exhaust cam. I don't think the cam lobes necessarily need to be aligned. But I hope someone can verify that for both of us.

 

[amc49]

The service manual is correct, the lobes AREN'T in line, the two cylinders would then have to fire at same time and they don't.

It's just that it is possible to set valves in more than one location as long as the checking point is on the 'base circle' of cam. The base circle is the part that would be left if you carefully ground off 100% of the lobe to be dead level at the cam, or simply a circle with no lobe at all.

Old school (the way I do it) has you setting them at the exact opposite of the lobe's highest point but then you end up cycling the motor around much more and it kills shop time doing the work. So, since the base circle is present up to maybe 30 degrees both before and after the lobe low exact center point, Honda makes marks so that you can set on both sides of the dead low middle. It gets bike out of shop quicker, ergo, more money.

In fact, the issue I tell you about the clearances being too close had them slightly change the marks up from the early ones, after around '82 or so they moved the marks to be somewhat different. I think they realized there were problems like I say with getting reliable valve clearance numbers.

You can move the lobe pairs to where the high point is dead 180 degrees opposite the tappet contact point on each pair of valves and set them just fine and all day long.

 

[The Jimbonaut]

Interesting, thanks amc for clearing that up

 

[Oliver Boy]

Thanks amc49
Wish I knew half what you do

 

[amc49]

I wish I MYSELF knew half of what I do......................

 

[Oliver Boy]

I have a question .....there may not be a good answer ....
How can all the valves end up so uniformly tight?
I'm currently on the lookout for a set of feeler gauges that measures thinner than .038 mm- otherwise I cant even measure what thickness shims I need to set things straight .
I'm wondering if I should order a set of ' sacrificial' thin sims to swap in, just so I can start to measure accurately.
Any thoughts please?
Thanks

 

[The Jimbonaut]

Those are some tight clearances you've got there - did you try rotating the cams on a particular cylinder until the lobes of the cams are directly opposite the valve shims? I'm guessing this would ensure the maximum clearance between cam and shim, and might allow you to get a feeler gauge in there easier.

 

[Oliver Boy]

Yes, just did it again.
All too tight.

 

[amc49]

The valves are made of crap low grade steel, the only thing that lets them live is the very thin nitride hardcoat over them. With that hardcoat missing (say if somebody 'thinks' he can grind the valve itself) the soft valve will die in only a very few thousand miles, less than 10 for sure. They were intended for an era of low lead fuel, not the zero lead we have now. Even very low leaded fuel actually improved valve life quite a bit over zero. Zero lets the valves recede, they slowly erode seat and valve material away to sink lower and lower into the head. In the time period they were intended the valves were intended to recede about the same amount as what they would loosen like most other engine types do, that then cancelled out wear. Once the lead disappeared though the recession happens faster than the wear.

The holes in head cams run in are looser (up to .008") than the valve clearances, that means the cams since fairly hard sprung will push the valve clearance around to eat some of it up, what you measure is not what is really in there real world and running. Why you go to .005" to set them instead of .003", pretty much 2 thousandths of whatever number you get there does not exist and why they burn valves at .003" and below.

That's also why you can move around on cam base circle or even measure closely to get the exact same checking spot over and over and STILL get slightly different clearance numbers every time you recheck, the cams move around a little bit different every time you roll the motor around.

I got the same tight everywhere on the first one I ever did and it freaked me out too. I burned several valves in less than 5K on a brand new bike thinking I was 'holding them close' at .003", some were as low as .002" and those are the ones that burned. Treat a check of .002" as zero and you will do fine. Why I bumped all setting to .005".

Whatever crosses your mind.............DO NOT turn engine with a shim out of the tappet, it will seize tappet up in bore and ruin head. You DO pretty much need a couple at least extra shims for checking to swap some of the ones you got to different locations.

Common issue on these, people just can't get head around the fact they commonly close up rather than get looser, why so many of the bikes sold are running like pure crap.

 

[Oliver Boy]

Thanks (again) amc
Much to think about; I have a spare engine which seems to have much better valve clearances- I think I'll get braves and prep the spare head for a swap.
I appreciate all your advice, now I have to get my hands dirty
Oliver Boy

 

[The Jimbonaut]

Hope you get everything worked out bud