Tappets

[MikeL46]

I run a tightly set 6 thou and 10 thou because I prefer the slightly milder cam timing it provides. It's a very small effect but noticeable. It also in theory cools the exhaust valve a little

Sorry, but tighter valve clearance equals slightly more radical cam timing and lift. And less time for the exhaust valve to sit on the seat and cool.

Mike

[barryh]

I run a tightly set 6 thou and 10 thou because I prefer the slightly milder cam timing it provides. It's a very small effect but noticeable. It also in theory cools the exhaust valve a little

Sorry, but tighter valve clearance equals slightly more radical cam timing and lift. And less time for the exhaust valve to sit on the seat and cool.

Mike

The opposite is true as 6 and 10 thou are a little wider than the book settings of 4 and 8 thou.

I think you may have misunderstood what I meant by tightly set. I meant not a fraction more than the specified 6 and 10 i.e. a tight sliding fit and with thumb pressure on the push rod end of the rocker arm to displace the oil film. Possibly 5.5 and 9.5 thou.

[Rob Frankham]

Rob said:”The clearances, set when cold, are, in fact, a way of achieving a minimal safe clearance at engine operating temperature without the complication and expense of adjusting when the engine is hot.”
The valve clearances do not change measurably with temperature. The clearances are to allow for long intervals between adjustments. You would be amazed at how powerful, smooth and quiet your engine will run with zero clearance. But then you’d have to check clearances every few hundred miles to be sure there is some, as (all?) racers do. Also, the recommendation to adjust valves when cold is primarily so the mechanic doesn’t burn his hands.

Rob also said:”The third part is to carry out a QC check. Turn the engine over at least once, preferably two or three times, and then check the clearances.”
You can recheck all you want, but turning an engine once, twice or a hundred times, does not affect valve clearances.

The method I described provides guaranteed in spec clearances with zero trial and error.
Feeler gauges, especially worn and bent ones, do not compensate for unevenly worn surfaces or operator inconsistencies.
Visualize a feeler gauge between a set of points that has a valley in one side and a peak on the other; your rocker arm to valve stem surfaces may be more like that than you think. They are rarely perfectly flat on a worn engine. Also, you can ask ten different people to set a gap with feeler gauges and get ten different results, depending on uneven wear and how tight or loose they decide the blade should fit between the parts. 1/6 of a turn, one flat of a hex, is a consistent no-brainer.


On my bike, I pop the covers off every oil change (5000kms) and check clearances by feel. I only have 520,000kms on my bike, so I'm not sure how my method will pan out in the long run but I'll keep you posted..

Oh and btw, for those of you who can't extrapolate, smidgeon means c%$@hair,

I'm sorry, you're not making any sort of sense. I'm not going to indulge in an extended argument. I would just suggest that you consider the following points...

1) If Push Rod engines can survive quite happily with no valve clearance, why in the name of the deity of your choice has every manufacturer of pushrod engines since time immemorial specified a valve clearance?

2) Except in the rather exceptional circumstances of VSR, valve clearances tend to widen with use not close up so the argument about valve clearances being there to allow for longer (5000 miles???) service periods is self evident nonsense.

3) If the bearing face on the tappet is starting to wear unevenly, then the valve clearance will alter from one revolution of the engine to the next because the tappet rotates in use. If the pushrod ends are wearing unevenly, the valve clearances will alter from one revolution to the next, the pushrods also rotate in use. Doing the job properly can detect these incipient problems.

Rob

Rob

[barryh]

I had a Matchless G3L single where the specified valve clearance was zero on a cold engine. The method was to adjust so that the pushrods would just spin with your fingers. I presume in that case the clearances opened up a little with a hot engine.

There used to be a tool sold called the SPQR tappet adjuster that used GSPD's method. It was based on the same principle of knowing the thread pitch and rotating by a set amount. It had a knob that could be turned through a number of clicks depending on the required clearance I think you can still buy them under a different name.

Going back to the original question, the exact clearance isn't all that important provided you adopt a method that gets both cylinders as close to the same as possible. Obviously zero clearance or less is not a good idea and at the other extreme if the clearances were set much too big you risk bypassing the clearance ramps on the cams so the valves would open and close too abruptly. I assume a noticeable increase in noise would let you know if that was the case.

[gspd]

With all due respect...
1)If Push Rod engines can survive quite happily with no valve clearance, why in the name of the deity of your choice has every manufacturer of pushrod engines since time immemorial specified a valve clearance?
Because if any manufacturer set them at zero BUT you had to check valve clearances every few hundred miles, nobody would buy that bike. I have friends who race with shim type valve adjusters (Ducati) and they get better dyno figures with zero clearance. They are constantly checking their clearances. On a desmo, checking clearances is relatively easy, but actually re-shimming is a tedious and time consuming PITA.
It's not necessarily a real advantage on the track because every body does it. Just ask any real racer, a smidgeon more power is always better than a smidgeon less..

2) Except in the rather exceptional circumstances of VSR, valve clearances tend to widen with use not close up so the argument about valve clearances being there to allow for longer (5000 miles???) service periods is self evident nonsense.
Sorry Rob, but in this case, you are completely mistaken. I've worked on dozens of cars over the years that were idling poorly because the valves were never checked and had tightened up over the miles. Too loose just clacks with very little ill effect except for maybe a slight power loss and somewhat accelerated wear. No big deal if its a beater. However, too tight will cause noticeable power losses, stalling and misfiring, and eventually burnt valves if not addressed. Ask any (very) experienced mechanic, they'll back me up.

3) If the bearing face on the tappet is starting to wear unevenly, then the valve clearance will alter from one revolution of the engine to the next because the tappet rotates in use. If the pushrod ends are wearing unevenly, the valve clearances will alter from one revolution to the next, the pushrods also rotate in use. Doing the job properly can detect these incipient problems.
Are you simply speculating? Have you actually witnessed this first hand? I never have. ever. If turning your engine over a few times changes your valve clearances, something is seriously wrong. I can't imagine what would cause that except for maybe chunks of carbon dislodging from the valves and/or seats and getting in the way...but I've never seen that either, usually the chunks just get blown out the exhaust.. If your clearances actually do change from one rotation to the next, how do you determine which rotation you will set them on? Rotating parts wear, but the their rotation generally assures smooth, consistently even wear patterns even if one part becomes convex and its mating part becomes concave..

[Rob Frankham]

With all due respect...
1)If Push Rod engines can survive quite happily with no valve clearance, why in the name of the deity of your choice has every manufacturer of pushrod engines since time immemorial specified a valve clearance?
Because if any manufacturer set them at zero BUT you had to check valve clearances every few hundred miles, nobody would buy that bike. I have friends who race with shim type valve adjusters (Ducati) and they get better dyno figures with zero clearance. They are constantly checking their clearances. On a desmo, checking clearances is relatively easy, but actually re-shimming is a tedious and time consuming PITA.
It's not necessarily a real advantage on the track because every body does it. Just ask any real racer, a smidgeon more power is always better than a smidgeon less..

The desmodromic valve setup isn't a pushrod system - irrelevant

2) Except in the rather exceptional circumstances of VSR, valve clearances tend to widen with use not close up so the argument about valve clearances being there to allow for longer (5000 miles???) service periods is self evident nonsense.
Sorry Rob, but in this case, you are completely mistaken. I've worked on dozens of cars over the years that were idling poorly because the valves were never checked and had tightened up over the miles. Too loose just clacks with very little ill effect except for maybe a slight power loss and somewhat accelerated wear. No big deal if its a beater. However, too tight will cause noticeable power losses, stalling and misfiring, and eventually burnt valves if not addressed. Ask any (very) experienced mechanic, they'll back me up.

If the valve seats have 'closed up' over the miles, that normally means they were set too close close in the first place and the exhaust seats are eroding. What other reason is there for valve clearances to tighten? In any case I didn't say 'will always' widen, I said 'will tend to widen' and I stand by that. Either way, if they are changing substantially between services, there is something wrong with the engine which needs to be looked at... which brings me to the next point...

3) If the bearing face on the tappet is starting to wear unevenly, then the valve clearance will alter from one revolution of the engine to the next because the tappet rotates in use. If the pushrod ends are wearing unevenly, the valve clearances will alter from one revolution to the next, the pushrods also rotate in use. Doing the job properly can detect these incipient problems.
Are you simply speculating? Have you actually witnessed this first hand?

Yes

I never have

If you don't check these things, you'll never see them.

. ever. If turning your engine over a few times changes your valve clearances, something is seriously wrong.

Exactly!!!

I can't imagine what would cause that except for maybe chunks of carbon dislodging from the valves and/or seats and getting in the way...but I've never seen that either, usually the chunks just get blown out the exhaust.. If your clearances actually do change from one rotation to the next, how do you determine which rotation you will set them on? Rotating parts wear, but the their rotation generally assures smooth, consistently even wear patterns even if one part becomes convex and its mating part becomes concave..

What you can't seem to get your head around is that servicing isn't just a matter of blindly doing a series of adjustments, by far the most important part of servicing is examining the parts to detect issues before they become serious problems. This is my main argument against your setting system... you blindly reset the clearances to what I would agree is a reasonably accurate setting without being able to detect whether (a) they need adjusting and (b) whether there is any signs of wear that would need further examination or attention. The main point of the service is completely missed.

Rob

[Rob Frankham]

I had a Matchless G3L single where the specified valve clearance was zero on a cold engine. The method was to adjust so that the pushrods would just spin with your fingers. I presume in that case the clearances opened up a little with a hot engine.

There used to be a tool sold called the SPQR tappet adjuster that used GSPD's method. It was based on the same principle of knowing the thread pitch and rotating by a set amount. It had a knob that could be turned through a number of clicks depending on the required clearance I think you can still buy them under a different name.

Going back to the original question, the exact clearance isn't all that important provided you adopt a method that gets both cylinders as close to the same as possible. Obviously zero clearance or less is not a good idea and at the other extreme if the clearances were set much too big you risk bypassing the clearance ramps on the cams so the valves would open and close too abruptly. I assume a noticeable increase in noise would let you know if that was the case.

I know of the SPQR adjuster. Wouldn't use it for the reasons discussed here. Just because someone makes a tool, doesn't mean it's good practice... In fact, one could take the position that 90% of these 'wonder tools' designed by aftermarket tool manufacturers are unnecessary. In my earlier days, when I was a little more gullible, I bought any number. Most of them have been thrown away or are sitting on the garage shelf unused. If it, or something like it, isn't used by the vehicle manufacturer, it probably isn't necessary.

Less than zero clearance isn't just 'not a good idea' it will destroy the engine in very short order.

One of the things I can't understand about this debate is why using a feeler gauge is thought to be in any way bad. It is a simple, quick procedure which produces a result that is accurate well within the requirements of the job being done. It's undoubtedly as accurate, probably more so than GSPDs 'guess the degrees and subtract a smidgeon method and it doesn't require a complicated special tool... and, if done properly, it will identify a number of developing problems...Why on earth do it any other way?

Rob

[gspd]

I like these exchanges with you, even if we don't always see things from the same perspective
You said" What you can't seem to get your head around is that servicing isn't just a matter of blindly doing a series of adjustments, by far the most important part of servicing is examining the parts to detect issues before they become serious problems. 

If you had ever worked in a new vehicle dealership, you’d understand that servicing IS EXACTLY "just a matter of blindly doing a series of adjustments." as specified by the manufacturer.
BMW dealers are all nuthouses during the riding season, especially in the spring. All those bikes that were stored over the winter hit the road in the spring. The newly sold ones are all back for their first checkup within a few weeks, not to mention the hordes of customers in for their annual 'tune-ups’ and the tourists in for emergency repairs. When you go through such a high volume of vehicles, and are required too do repetitious maintenance over and over and over, you MUST develop ways to do things more efficiently.

If a customer simply comes in for a routine valve adjustment, and has no specific issues, I really don’t give a crap what the settings are when it comes in. The mission is that it leaves properly within specs. Period. This is fine for 99.9% of the bikes, 99.9% of the time..There is simply no time or need to turn the engine over and over to recheck things ‘just in case’. There is no time for “examining the parts to detect issues before they become serious problems“ when experience has proven that these 'serious problems’ are the very very rare exception rather than the rule.

Unfortunately there’s always the noisy old clacker, the one with the receding seats, the moron with the flywheel on wrong so you can’t use the timing marks, the one with the bodgered adjusters, oh and if the owner attempted to fix it first, the one with the rocker studs pulling out of the block and stripped valve cover fasteners.
These .1% of ‘oddballs’ with actual problematic issues are dealt with on a totally different playing field, and will usually require that extra degree of attention that the majority machines on the road will never require or miss.
After decades of experience, I can often pick out those oddballs at a glance, even from across the parking lot.

[Rob Frankham]

Of course, that's why my bikes never see the inside of a stealership.

Rob

[Zombie Master]

Now that's a Boxerworks thread!