MG Motorsports Forum
Valve lash
Posted by mgbrv8
Valve lash
#1
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Topic Creator (OP)
Mar 1, 2015 11:51 AM
Joined 12 years ago
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Topic Creator (OP)
Mar 1, 2015 12:18 PM
Joined 12 years ago
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About 12 miles from Sears Point, CA, USA
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Mar 2, 2015 01:39 AM
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Joined 17 years ago
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.012" hot is the minimum I would run.
Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
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More Cars than Brains
Basil C. Adams
1956 MGA Coupe (Show Car)
1957 MGA Roadster (Driver)
1958 MGA Coupe (Racecar)
1959 MGA Coupe (unrestored)
1960 MGA Coupe (unrestored)
1960 MGA Roadster (Driver)
MKIII Elva Courier (E1056)
1967 427 Cobra
1972 Alfa Romeo Montreal
A coupla late MGBs
1960 Austin Healy BN7
More Cars than Brains
Topic Creator (OP)
Mar 2, 2015 01:48 AM
Joined 12 years ago
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Mar 2, 2015 02:23 AM
Joined 16 years ago
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Lash is designed into the cam, varies by cam design; Going much off that is not good. Final at the valve lash varies by all the parts in between, and the materials they are made from. Many engines run .006 -,008; some are actually set at zero(cold), or better yet "zero - tight" for inlet, and "zero - loose" for exhaust. As I found out, if you set the valves on a nice warm day, you have no compression when it drops to zero deg F.
FRM
FRM
dipstick
Kenny Snyder (RIP)
La Center, WA, USA
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1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie" 1970 MG MGB GT "Pat's GT" 1971 MG MGB "Gifted To Me" & more |
Mar 2, 2015 09:20 AM
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Mar 3, 2015 09:43 AM
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Thanks Kenny. Here's a question. I typically set my lash by putting my car in 4th and rolling it 10 feet or so, back and forth. The download that you reference seems to indicate that it is important to only move the engine in it's proper rotation. Could that be why my lash seems to change even on an immediate re-check? I have been struggling with getting a consistent setting.
D.
Douglas Tourtelot
Seattle, WA
"Every education has a tuition"
D.
Douglas Tourtelot
Seattle, WA
"Every education has a tuition"
dipstick
Kenny Snyder (RIP)
La Center, WA, USA
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1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie" 1970 MG MGB GT "Pat's GT" 1971 MG MGB "Gifted To Me" & more |
Mar 3, 2015 10:53 AM
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Doug, Good question about direction of rotation (#2). I do adjust the lash in the direction of rotation to be sure the timing chain & tensioner remain tight, to be sure that the cam is on the center of the lobe base circle (not considering cam advance/retard). I too roll the car in 4th, but only in one direction.
Truth is that I don't use the "rule of nine". I use the top-dead-center mark on the harmonic balancer, and another mark I made on the other side 180* away. On the top-dead-center mark I adjust both the intake & exhaust valves for one cylinder (say cyl. #1) knowing that both lobes are in the center of their base circles, then rotate the crankshaft 180* to the opposite TDC mark and adjust the next intake & exhaust in the firing order. I also cut a groove across the forward face thru the inner & outer rings so I can tell if the outer (floating) ring has moved.
Be safe out there.
Kenny
Truth is that I don't use the "rule of nine". I use the top-dead-center mark on the harmonic balancer, and another mark I made on the other side 180* away. On the top-dead-center mark I adjust both the intake & exhaust valves for one cylinder (say cyl. #1) knowing that both lobes are in the center of their base circles, then rotate the crankshaft 180* to the opposite TDC mark and adjust the next intake & exhaust in the firing order. I also cut a groove across the forward face thru the inner & outer rings so I can tell if the outer (floating) ring has moved.
Be safe out there.
Kenny
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Dave Headley
Cortez, 4 corners, Colorado, USA
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Mar 3, 2015 12:14 PM
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Re: Valve lash
#10
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Mar 3, 2015 01:31 PM
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"base circle" amounts to a minimum of half the cam circumference, or a complete turn of the crank, so there is nothing critical here. As Dave says, at TDC no tappet is " at the center", but it doesn't need to be. There is no need to worry about "exactly", so far as position goes. Also doesn't matter which way you turn the engine for this, but in general it is good to get in the habit of only turning it the normal direction.
Have the plugs installed to adjust valves the easy way. A four cylinder engine with compression in all four will naturally come to rest in one of two crankshaft positions - you can see this by looking at the flywheel gear, where you will see the two wear areas. At each crank position, there are two possible cam positions, for a total of four. Each of these will have a pair of valves (example1&3) pretty much open, ie on the lobes, which leaves the pair (6&8) mirror opposite (by "rule of 9"on the base circle. Adjust those. A quick hit on the starter will advance the engine to the next pair - 4 hits and you are done. Good to disable the spark, though most engines will not fire in a half turn, so I usually don't.
If the engine will not stop in all four positions, it is a good indicator that one or more cylinders have low compression. If you are lucky, this will be because the valves are very far out. In that case just turn the engine through two turns adjusting by "rule of 9". If it still won't stop in all 4 positions, it is past time for the compression gauge.
If you get varying measurements, you have a bad tappet, valve sticking in guide, or debris on a valve seat - those are the only likely things that can change clearance in a few revolutions. Otherwise, it is a measuring error.
FRM
Have the plugs installed to adjust valves the easy way. A four cylinder engine with compression in all four will naturally come to rest in one of two crankshaft positions - you can see this by looking at the flywheel gear, where you will see the two wear areas. At each crank position, there are two possible cam positions, for a total of four. Each of these will have a pair of valves (example1&3) pretty much open, ie on the lobes, which leaves the pair (6&8) mirror opposite (by "rule of 9"on the base circle. Adjust those. A quick hit on the starter will advance the engine to the next pair - 4 hits and you are done. Good to disable the spark, though most engines will not fire in a half turn, so I usually don't.
If the engine will not stop in all four positions, it is a good indicator that one or more cylinders have low compression. If you are lucky, this will be because the valves are very far out. In that case just turn the engine through two turns adjusting by "rule of 9". If it still won't stop in all 4 positions, it is past time for the compression gauge.
If you get varying measurements, you have a bad tappet, valve sticking in guide, or debris on a valve seat - those are the only likely things that can change clearance in a few revolutions. Otherwise, it is a measuring error.
FRM
Re: Valve lash
#11
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Topic Creator (OP)
Mar 3, 2015 02:29 PM
Joined 12 years ago
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Re: Valve lash
#12
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at the glen
Jim Acquilano
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Mar 3, 2015 05:15 PM
Joined 9 years ago
179 Posts
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Re: Valve lash
#13
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dipstick
Kenny Snyder (RIP)
La Center, WA, USA
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1941 Ford N-Series
1958 MG MGA 1500 Coupe "Rosie" 1970 MG MGB GT "Pat's GT" 1971 MG MGB "Gifted To Me" & more |
Mar 3, 2015 05:18 PM
Top Contributor
Joined 15 years ago
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Kenny said, "... knowing that both lobes are in the center of their base circles ..."
I should have not used the phrase "center of their base circles" at TDC, but I a remain convinced that for a given cylinder both the intake & exhaust valves at TDC are definitely on the base circles of both camshaft lobes, not onto the acceleration ramps of the lobes. Were the lobes not on the base circles of the lobes why would the lash be set in any other position? Is somebody going to tell me that at a given cylinder TDC firing stroke both the intake & exhaust valve tappets are not on both the intake & exhaust camshaft base circles?
Be safe out there.
Kenny
I should have not used the phrase "center of their base circles" at TDC, but I a remain convinced that for a given cylinder both the intake & exhaust valves at TDC are definitely on the base circles of both camshaft lobes, not onto the acceleration ramps of the lobes. Were the lobes not on the base circles of the lobes why would the lash be set in any other position? Is somebody going to tell me that at a given cylinder TDC firing stroke both the intake & exhaust valve tappets are not on both the intake & exhaust camshaft base circles?
Be safe out there.
Kenny
Re: Valve lash
#14
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Mar 3, 2015 05:52 PM
Joined 16 years ago
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Re: Valve lash
#15
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Topic Creator (OP)
Mar 3, 2015 06:09 PM
Joined 12 years ago
329 Posts
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