Piston to valve clearance

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Gator417
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Piston to valve clearance

#1

Post by Gator417 »

My '77 GL has at least one blown head gasket (poor Nora). I think its been this way since I got it and just got super bad when she got a little hot on a recent ride. Coolant rolling out of the tail pipe bad. While the heads are off, I figured I'd get them decked and bump up the compression just a tad. I just need to know how much can be taken off without having clearance issues. I've read dozens of threads and web pages and haven't found anything remotely close to what I need. I know how to measure with modeling clay et al, but I'd rather not go through the hassle if someone has already done it, or otherwise knows where I can find that value.
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robin1731
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Re: Piston to valve clearance

#2

Post by robin1731 »

Can't answer you question. But do be aware that as you remove material from the head you change cam timing.
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ericheath
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Re: Piston to valve clearance

#3

Post by ericheath »

I took 0.025" off 77 heads, but put them on a 1200 block. I had the pistons notched on the intake side to be sure they would clear. Pistons are less domed on 1200's. I couldn't find data either. I think I calculated that I lost 0.6 degree in cam timing with the shave. I recently advanced the cams to get that back and a little more. So far, so good.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
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oldwings 78
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Re: Piston to valve clearance

#4

Post by oldwings 78 »

+1 Robin. I would only have the machine shop take enough material off the heads to get them flat again. I do want to know how the valve timing can change by milling a few thousandths off. The number of cogs on the crankshaft and camshaft are the same, just a few thousandths closer together right?
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EDIT oops, duh! I read my post and answered my own ???????? (a few thousandths closer)
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Re: Piston to valve clearance

#5

Post by chewy999 »

oldwings 78 wrote:+1 Robin. I would only have the machine shop take enough material off the heads to get them flat again. I do want to know how the valve timing can change by milling a few thousandths off. The number of cogs on the crankshaft and camshaft are the same, just a few thousandths closer together right?
Terry
EDIT oops, duh! I read my post and answered my own ???????? (a few thousandths closer)
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1980 CB250N Good to learn on
1981 CX500 good mid range tourer, went to Austria on it!
1983 GL1100C Pride and joy, sold when I bought my 1st house, big mistake
1985 GL650 Silverwing another mistake, horrible bike
1986 CBX550 Good commuter
1989 Suzuki GS750 (1976) cheap and cheerful until a dog ran out in front of me on Xmas Eve, 1991
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ericheath
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Re: Piston to valve clearance

#6

Post by ericheath »

Terry, the few thousandths off the head move the cam gear backwards. Because the teeth on the belt remain fixed. I calculated it as 4.7" dia of cam gear * pi = 14.766 circumference of cam gear---- 360 / 14.766=24.38 deg per inch---- 0.025*24.38= 0.6095 degrees at the cam.

That would be 1.2 degrees at the crank.

Interestingly, that same 0.025 at the cam keyway translates to is closer to 4 degrees because the cam shaft is so much smaller.

Now, I've been wrong before, so.............
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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Re: Piston to valve clearance

#7

Post by robin1731 »

ericheath wrote:Terry, the few thousandths off the head move the cam gear backwards. Because the teeth on the belt remain fixed. I calculated it as 4.7" dia of cam gear * pi = 14.766 circumference of cam gear---- 360 / 14.766=24.38 deg per inch---- 0.025*24.38= 0.6095 degrees at the cam.

That would be 1.2 degrees at the crank.

Interestingly, that same 0.025 at the cam keyway translates to is closer to 4 degrees because the cam shaft is so much smaller.

Now, I've been wrong before, so.............

My head hurts, that's too much math. ;) Put a degree wheel on it in stock form and then after moving it. That will tell you exactly where it is. :orange
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
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ericheath
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Re: Piston to valve clearance

#8

Post by ericheath »

Degree wheels need to be calibrated and set properly, and you have to know how to use them. Math is exact. I've been in school 50 years, but I'm still in fourth grade. So my math could be wrong. My numbers could be off a little as I haven't checked my calipers for a while. One of these days I'll pick up a wheel and learn to use it.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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Re: Piston to valve clearance

#9

Post by Gator417 »

Right, if the idler took up the slack form both sides of the belt, no change, I get it. I do like me some math, but I'm not the slightest bit worried about 1-2 degrees of cam timing, its never that accurate anyway. Unless you have an adjustable cam sprocket, you'll always be off a bit. What I am concerned with is finding an answer to my question. So if I don't get my answer here, you can bet I will find it myself and report back. Thanks for your responses.
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ericheath
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Re: Piston to valve clearance

#10

Post by ericheath »

I think you will have to. I've been hanging around here for ten years and don't remember anyone reporting it, unless Oldboy did it on his 1100. That wouldn't answer your question for a 1000. My gut says it will be okay, but you'd be best to use some clay and model it at the stock spot. That would give you an idea if you can go very much. It would give it some more punch at the lower rpm.
Whatever I suggest here should be given ample time for a moderator to delicately correct. I apologize in advance.
77 WING, 1200 engine with 77 heads, cams, gl1100 foot pegs, Magna V65 front end, 764A carbs, [-gone Suzuki M109 monoshock--, replaced with gl1100 shocks] gl 1200 swing arm, gl1500 final drive, wheel and rear brakes Valkyrie seat, Meanstreak tank, Sportster pipes, Power Arc ignition off crank.
77 Wing. black
83 Wing, in pieces
"Continuing education is important even if the subject matter is fairly useless (as in this case)."---Greg Foresi
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robin1731
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Re: Piston to valve clearance

#11

Post by robin1731 »

ericheath wrote:Degree wheels need to be calibrated and set properly, and you have to know how to use them. Math is exact. I've been in school 50 years, but I'm still in fourth grade. So my math could be wrong. My numbers could be off a little as I haven't checked my calipers for a while. One of these days I'll pick up a wheel and learn to use it.

LOL, there is math when using a degree wheel too. But after so many you can do it pretty quickly.

Degree wheel and a dial caliper is all you really need. Positive piston stop is useful too. But about the only way to use that right is to set the wheel up before installing the heads.
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
Gator417
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Re: Piston to valve clearance

#12

Post by Gator417 »

Yeah, that's what I figured. I thought I read about it once here, but there was no solid number given. I don't mind doing it myself, but it will be my first time, so we'll just see how it goes. I'll have to measure the combustion chambers as well, to see how much shaving will increase the CR. More math, but at least I've done that one before.
On another note, I think 9.2-1 CR is a little on the weak side. I'd really like to have it up around 11-1, but any increase will be just fine with me. My ignition is pretty hot (electronic ignition and MSD coil) so I think she'll be OK in that area. She woke right up when I trashed the original setup. Very excited to get her back on the road, and its nice to know this gasket may have been the source of my slightly rough idle and smokey (steamy?) start ups. Also going to hit some cosmetic issues, fix the neutral switch, lights, mirrors, repaint exhaust and wrap the headers befor buttoning her up again.
Thanks again,
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robin1731
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Re: Piston to valve clearance

#13

Post by robin1731 »

Easy way to raise compression. Bore the cylinders. ;)

This also unshrouds the valves some.
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
Gator417
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Re: Piston to valve clearance

#14

Post by Gator417 »

How is that an easy way to raise the CR?
Remove engine, split engine and diassemble, send engine to machine shop, buy new pistons and rings, buy a bunch of new seals and gaskets, reassemble engine, reinstall engine, rejet carbs. Not to mention, I would still have to do all the work I have to do anyway, to fix the head gaskets. Not following you here.
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Last edited by Gator417 on Wed Oct 08, 2014 10:38 pm, edited 2 times in total.
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Re: Piston to valve clearance

#15

Post by robin1731 »

Gator417 wrote:How is that an easy way to raise the CR?

Take the same pair of heads. Rather than put them on a 1000 you can put them on an 1100. You can put them on a 1200 too but you have to open the valve reliefs in the pistons.

Yes I did say bore them out. And that would be more work. But swapping lower ends is pretty easy.
1976 Goldwing Super Sport
1985 Honda Elite
1976 KZ900 Dragbike
1992 ZX7 Dragbike (KZ900 style motor w/NOS)
and a rotation of various purchases
Randakk approved Carb Rebuilder
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