Piston to valve clearance

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Casper
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Re: Piston to valve clearance

#31

Post by Casper »

I'll keep watching this thread, gator let us know how it all turns out for you.

Cheers,
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passx
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Re: Piston to valve clearance

#32

Post by passx »

On my bike when I clay'd the pistons it required no mods to the pistons which is why I did the clay thing to begin with to see what was going on in there since I'd advanced the cams to move the power down. When you do that it moves the intake valve sooner and creates more clearance but it opens the exhaust sooner as well which means the piston is higher in the bore and less clearance there. I know when I was building hotrod engines you want about .060 in. clearance on the intake and .080 in. on the exhaust, as far as mine I can't remember exact numbers because it's been about 10 years or so since I've done that. THe great thing about this is that the power is way more tractable between the cam advance and the compression increase from the heads. You'll find that you need to downshift less and it's always ready to go. When I did the cam advance I had access to running it on a dyno and it actually lost 2hp peak but it picked up 2 ft/lb and the curve was more squared up so that at a lot of points it made 10-12 hp and ft/lbs more, it only varied from peak torque by 2 ft/lbs from 2200 to 6800 rpm. Also as you're doing this I recommend you rejet the carbs. Put #65"s in the primary mains and 115's in the secondary mains, this will help richen the bottom end up where it's very lean and they checked the emissions up to 2200rpm and then it'll lean the top out that's extremely rich, typically 10-10.5 a/f ratio. That is what gives you that "on the cam" or "on the pipe" sensation, it's not a power increase per se it's just where the motor finally clears the glob of fuel out and starts to run clean from when you whacked the throttles open, you'll like it.

Steve P.
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Re: Piston to valve clearance

#33

Post by Gator417 »

Steve,
How do you do this cam advance of which you speak? I do not have access to a dyno, but I will trust a fellow Hoosier. I think my carbs are already 65 & 115, but I'll have to look at my records to make sure. Do you know what the stock jets are for this year? Very excited to have some real first hand experience here & looking forward to having some more torque and hp where it matters.
Thanks again,
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Re: Piston to valve clearance

#34

Post by ericheath »

75 came with 65 pri, 125 main. 76 and 77 came with 62pri, 120 main. I chased jetting all over when I did this to my hybrid, 1200 with 77 heads, cams, carbs and 0.025" shaved. Finally decided to change the speed at which the slides opened by blocking one of the three holes in the bottom of the slides. Seemed to cure it. I am back to nearly stock jetting. I think my primary is around 70. I have run it for two weekends with the cams around 2.5 degrees advanced and the power curve feels more like Steve describes. When I took it to 4 degrees advanced, it would hit a wall at 7300 just like a rev limiter. In messing with the 2.5 degree advance, I also set my ignition timing to 10 degrees rather than 5 degrees like a 77. That may have been causing my " rev limiter." I might try it back to 4 degrees with the ignition timing advanced as well.
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.
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alwing17
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Re: Piston to valve clearance

#35

Post by alwing17 »

Hey Steve...Glad to see you are onboard action1 Lots of great guys on the board here.
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Re: Piston to valve clearance

#36

Post by passx »

Guy's,
Eric is correct on the jet sizes. I was lucky to spend a lot of time on a Dynojet dyno and seen a lot of Keihin carb'd bikes run on it and they all showed the same stock results on the jetting regardless bike, from my GL1000 & CBX to Harly's and Valkeries.
All ran 15-15.5 to 1 on the low speed circuit up to 2000-2200rpm and then pig rich above at about 10-10.5 to 1. The 65 primary main helps a little on the bottom and helps cover the transitional stumble and the 120 o 115 secondary mains 10-10.5 to 1 lean the top down to around 13-13.7 to 1 depending on the bike. I too played with the slide holes by blocking 1 of them and this made the slides very sluggish and this showed as the same in the bike, so you'd think drilling an extra hole would be the answer but not so because it now opens too fast and throws even more fuel to the blob that's drowning your engine when you whack the throttles open. The slide vacuum holes are pretty well balanced as is, don't mess with them. Eric on my 1000 I added a set of highly machined and modified 1100carbs and had the same rev limiter effect, the thing just quit pulling rpm at about 7800 which initially I attributed to the smaller 1100 carbs BUT I had them off this spring for another problem and changed the main jets from the stock 145's to 140's and holy crap it now rev's freely to 9k and above. On the cam advance, I had a machine shop EDM 3 new key ways at +2,+4 and +6, the +6 setting gave the overall best cranking compression which says that's the best setting but this was only 2psi better than the +4 setting and as eric said advaning the cams moves the power band down in the curve so prudence said put it at +4 which by the way I verified with a degree wheel to be about +3.5 after the head cutting. If these were DOHC motors you could play with intake vs exhaust cam timing which on my 80 CBX went from -5 (production tolerances and wear) to +5 on the intake cam and the exhaust at 0 which I left alone, this gave a +2 hp bump and a +5 tq bump plus like the GL squared up the power curve, way better !! On the GL's I'd now just have a +4 keyway cut in and call it a day. Hope this helps answer some of the questions.

Steve P.
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Re: Piston to valve clearance

#37

Post by passx »

Thanks Dr Al, I've been lurking here for a while but haven't really got involved just because of time constraints but our friend Ed M. asked me to comment on the head cutting thing and it's kind of blossumed from there. It's really interesting about how much power Honda left on the table with these motors and most of it was in the carbs which they generally ran real rich to keep the warranty stuff down plus once you get them jetted exactly right they then become weather sensitive because you've jetted it to whatever conditions were that day, Hondas answer to that was just make them rich so they essentially run the same all the time, makes the consumer & accountants happy ya know. I did a 2000 Valkerie for a friend of mine where I opened the ports up and lots of time in the carbs and got the jetting good and I told him that it would be a little weather sensitive which he said he didn't care about but he couldn't quit messing with it until he had it totally messed up and it came back to sort it out, a process repeated two more times before I said "no more".

Anyway good to hear from you Al, hope all is well over there
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Re: Piston to valve clearance

#38

Post by ericheath »

I went out this morning and bumped it back to about 3.5 advanced. My ignition timing around 11 degrees. I opened my plug gap to about 0.037. It's wet here so no chance to pull it much. I did take it out and it felt a bit sluggish compared to before, but second gear at 4500 it would break loose. Hopefully it dries out a bit this afternoon. I never learn to do one mod at a time!! I should go back to ten degrees advance and left the plugs alone. I did take the rpms up moderately and it sputtered a bit at around 7500-8000 and then took off again. It makes me think it might be running out of fuel. A Dyno would be nice. Changing jets is a pain on these.

As to my bike and the slide holes, remember I have 300ccs drawing in what was supposed to be 250ccs. I'm thinking the additional vacuum is pulling the slides up faster. I may need to jet up one, but I may put a washer under the needle first as it's easier.

You are a welcome addition, Steve, as it appears you have experience and some years with real data. Any chance you have some Dyno charts around we could gaze at?
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.
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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

#39

Post by joedrum »

well this is like confromation on what i know to be true......cv carbs are not for me ..... when you put 1000 early cams in a 1200 ... i think its completely different in valve timing ...than when its in 1000 or 1100 motor....my friend dan put 1200 cams in 1100 and compression went up ... everything done at tdc and timed right .... playing with compression and cv carbs is not going to fix cv carbs problems ... after running the proggressive weber as long as i have .. it really obvious the carbs really hold back the motor ...my bike runs like a oldwing rocket hunter .... great post steve... it confirms what i already knew ..
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Re: Piston to valve clearance

#40

Post by Gator417 »

ericheath wrote:Any chance you have some Dyno charts around we could gaze at?
+1 for that. As well, would you have a photo of one of these cam wheels you have had modified? I'm just trying to get a mental image of what's going on there, but its till sort of vague to me.
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Re: Piston to valve clearance

#41

Post by canuckxxx »

I'm going to show my ignorance here because I have never done this; but wouldn't it be possible to measure valve/piston clearance by turning engine to TDC on exhaust stroke and then push the exhaust valve down till it touchs the piston? Maybe have a zeroed dial indicator on top of the valve spring to measure the movement.

Thanks for your patience :oops:
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Re: Piston to valve clearance

#42

Post by robin1731 »

canuckxxx wrote:I'm going to show my ignorance here because I have never done this; but wouldn't it be possible to measure valve/piston clearance by turning engine to TDC on exhaust stroke and then push the exhaust valve down till it touchs the piston? Maybe have a zeroed dial indicator on top of the valve spring to measure the movement.

Thanks for your patience :oops:
Brian

That works but it isn't the point where the valve is closest to the piston. And pushing the valve with that much spring pressure isn't the easiest. On race engines we assemble the head with just one set of valves using very light springs. Get the cams degreed in and then do what you are talking about. but with the springs we use we can push the valve in by hand. Just a finger really. But, TDC is not when the valve is closest in the cycle.
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Re: Piston to valve clearance

#43

Post by hoganJr »

robin1731 wrote:
canuckxxx wrote:I'm going to show my ignorance here because I have never done this; but wouldn't it be possible to measure valve/piston clearance by turning engine to TDC on exhaust stroke and then push the exhaust valve down till it touchs the piston? Maybe have a zeroed dial indicator on top of the valve spring to measure the movement.

Thanks for your patience :oops:
Brian

That works but it isn't the point where the valve is closest to the piston. And pushing the valve with that much spring pressure isn't the easiest. On race engines we assemble the head with just one set of valves using very light springs. Get the cams degreed in and then do what you are talking about. but with the springs we use we can push the valve in by hand. Just a finger really. But, TDC is not when the valve is closest in the cycle.
This is a fascinating discussion, even though I understand very little of what I read. You put play-doh in the cylinder to measure piston/valve clearance? And how can TDC not be the point at which the piston is closest to the valve?

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Re: Piston to valve clearance

#44

Post by CYBORG »

When the piston is at TDC the valves are closed. They open 5-10 degrees of crank rotation before the piston reached TDC. The playdough idea will work ,but involves several removing and replacing of the head
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Re: Piston to valve clearance

#45

Post by robin1731 »

The exhaust valve is closest to the piston as it is nearing TDC. So the piston is moving up toward the exhaust valve as it is closing. We shoot for about .070" of clearance between the exhaust valve and the piston on a race engine. The intake valve is opening as the piston moves down, just after TDC. On that we shoot for .030" valve to piston clearance.

In a perfect world you could have 0"-.001" clearance. But with thermal expansion and things going crazy in an engine you need some space. As rpm increases things happen faster so you need that margin for safety.

Look on youtube. There are some vids showing inside an engine on what a valve does as it cycle through. They can bounce off of the seat as they close. Pretty cool to watch but scary at the same time.
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1985 Honda Elite
1976 KZ900 Dragbike
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and a rotation of various purchases
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