valve clearances
- Thread starter mcns
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I have found that the amount of wacking/running the engine in high RPMs with rapid acceleration makes the valves go out of adjustment more frequently that doing the harley shuffle - are you a putt-putter?
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Something to check re this...
When I disassembled my top end I discovered that the EX valves had rather deep pits in the stem tips where the adjuster screws contacted them. THis meant that my valve adjustments were off be a couple of thousandths because the flat feeler blade can't tell there was a pit there. I wondered why the valves seemed to be clattering a bit more than they should. You can't tell this is happening without unscrewing the adjuster far enough to be able to see the top of the valve.
The adjuster screws were also badly pitted...New AN valve adjusters didn't look much better but I won't go off again on my AN parts quality rant!
When I disassembled my top end I discovered that the EX valves had rather deep pits in the stem tips where the adjuster screws contacted them. THis meant that my valve adjustments were off be a couple of thousandths because the flat feeler blade can't tell there was a pit there. I wondered why the valves seemed to be clattering a bit more than they should. You can't tell this is happening without unscrewing the adjuster far enough to be able to see the top of the valve.
The adjuster screws were also badly pitted...New AN valve adjusters didn't look much better but I won't go off again on my AN parts quality rant!
While flogging the engine definitely affected clearances in the past, mushroom-headed tappets have practically eliminated valve adjustments since I installed them years ago. I'm not usually an early adapter but in my Combat they've been beyond reproach for many, many miles.
Tim K
kraakevik@voyager.net
Tim K
kraakevik@voyager.net
Replaced both exhaust adjusters with RGM parts in Mar 09 and one has really chewed up a valve in 4000 miles. But, to be fair that valve was starting to show significant wear. These were not AN items so I replaced with one of theirs and a new ex valve. The AN profile is a little different from RGM. The AN item better be good with the UK price at £6.50 now...$10!! The exh valve tips have a hard time with the angle they operate at, compared to inlets.
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What is a "compression plate?" How does it change valve geometry?
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Gee - I've always called such a thing a "spacer". Interesting how terminology changes from place to place :wink:
Replaces the base gasket (if you use one) which is around 0.015". My plate is 0.030". So, it lifts the barrels and head which is compensated for by backing off the valve adjusters and therefore I don't see how it affects valvetrain geometry much. Yes, the rocker and adjuster contact angle will change but by how much? Is it enough to justify shortening pushrods which is the recommendation with high lift cams and substantially shaved heads and is what I did when I found std length rods in my engine with a Combat cam and head. Since then I went back to a std cam and have just installed a PW3. Will have to see how wear develops this year.
I have a 72 non Combat with a Combat head, 32mm carbs and big bore exhaust. This thing would scream. I had to de-tune. Because I had standerd pushrods, I sandwiched the plate between 2 base gasgets and put on a single 36mm Mikuni. With the 40 thou added this should have brought the geometry back home, assuming the the head lost 40 thou or so from the factory.
With the big bore exhaust retained it is a great highway runner. The "MAIN WORD OF CAUTION" is to either hone the piston ridge out of the bore completely or if need be bore to the next level. This ridge can raise havic on rings with the new location of the cylinder wall.
With the big bore exhaust retained it is a great highway runner. The "MAIN WORD OF CAUTION" is to either hone the piston ridge out of the bore completely or if need be bore to the next level. This ridge can raise havic on rings with the new location of the cylinder wall.
Keith1069 said:Replaced both exhaust adjusters with RGM parts in Mar 09 and one has really chewed up a valve in 4000 miles. But, to be fair that valve was starting to show significant wear. These were not AN items so I replaced with one of theirs and a new ex valve. The AN profile is a little different from RGM. The AN item better be good with the UK price at £6.50 now...$10!! The exh valve tips have a hard time with the angle they operate at, compared to inlets.
Mine looked like that a couple of years ago, I shortened them back and fitted lash caps, and due to my ex seats being a bit deep was able to adjust the rocker contact angle a wee bit, after re torquing and final setting I had to close them up by 0.001-0.002'' for the first time in 18 months.
Something to ponder on your old antique motor, at 6000rpm the top of each valve is being hit 50 times a second, its a wonder they last at all :!:
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splatt said:
Unless the valves are floating hopefully it's more of a push than a hit. :mrgreen:
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