86 Evo - specs on cyl/heads
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86 Evo - specs on cyl/heads
Trying to give her a little more go juice. I got the heads ported and polished the way I want and started looking into how much to mill off the heads. So with bloody fingers I continued.....
I will get more specific numbers but it looks like the top of the piston is .200 to .250 below the top of the cylinder.
I honed and re-ringed it before I put the motor on the bike - I have a slight tight spot on the front of the front cylinder. I was only getting 90 psi out of each jug.
The head gaskets are at .047" after pulling them off....my new screamin eagle gaskets are right at .020" before installation.
I originally wanted to mill out about .060 off the heads - - to bring my static compression to around 130psi (or whateve that would give me).
It is bored and stroked to 96 inches and has s&s pistons - I will get the model numbers.
It seems that the top of the piston should be at or just under the top of the cylinder - but if I try to mill off .200 from the bottom/top of the jugs the intake probably won't fit - and that is just a whole lot of milling so I want to look into it before I start grinding.
I will clay the valve clearance with the old gaskets tonight, and get the piston model numbers and post them up.
It just seems that stock jugs should be stock jugs (I already had to take .007 off of them to get them to seal up)...and I just can't see taking .250 off them - feels like bad juju.
I will get more specific numbers but it looks like the top of the piston is .200 to .250 below the top of the cylinder.
I honed and re-ringed it before I put the motor on the bike - I have a slight tight spot on the front of the front cylinder. I was only getting 90 psi out of each jug.
The head gaskets are at .047" after pulling them off....my new screamin eagle gaskets are right at .020" before installation.
I originally wanted to mill out about .060 off the heads - - to bring my static compression to around 130psi (or whateve that would give me).
It is bored and stroked to 96 inches and has s&s pistons - I will get the model numbers.
It seems that the top of the piston should be at or just under the top of the cylinder - but if I try to mill off .200 from the bottom/top of the jugs the intake probably won't fit - and that is just a whole lot of milling so I want to look into it before I start grinding.
I will clay the valve clearance with the old gaskets tonight, and get the piston model numbers and post them up.
It just seems that stock jugs should be stock jugs (I already had to take .007 off of them to get them to seal up)...and I just can't see taking .250 off them - feels like bad juju.
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Joined: Sep 2007
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From: Bluffton, South Carolina
It sounds to me like you have the wrong pistons. It appears you have some "stroker" pistons. They move the wrist pin up closer to the top of the piston to offset the increased stroke. If you use them in a stock stroke engine you will have what you described. If you put a stroker in and order pistons for a longer stroke the results will be the same. DO NOT SHORTEN YOUR JUGS THAT MUCH !!! Hope this helps.
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From: NC USA
I've not messed with strokers, but the above notion makes perfectly good sense to me.
There's a term" called "decking" which describes the check you did for "piston top below top of jug distance." For whatever it's worth, the stock, preferred or generally speaking, necessary distance is .040 with the jug half torqued on a used base gasket, measuring from the top of the cylinder liner to the top of the piston in the center. (not in the notch)
Something is definetly wrong with your setup. (no offense) A bone stock Evo, properly broken-in with low to moderate mileage will generally pump 155 - 160 compression at crank-over speed.
Keep us posted...
There's a term" called "decking" which describes the check you did for "piston top below top of jug distance." For whatever it's worth, the stock, preferred or generally speaking, necessary distance is .040 with the jug half torqued on a used base gasket, measuring from the top of the cylinder liner to the top of the piston in the center. (not in the notch)
Something is definetly wrong with your setup. (no offense) A bone stock Evo, properly broken-in with low to moderate mileage will generally pump 155 - 160 compression at crank-over speed.
Keep us posted...
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Exactly
Measurements: The cylinder sits .220-.223 below the top of the cylinder (decking).
What you are describing is the conclusion that I came to over the weekend. The cylinder was bored to 3-5/8" and they put a stroker piston on, but either did not replace the connecting rods or maybe the crankshaft is stock.
Why can't I take that much off the heads? I have read several about several mods that took .080 off - and I personally have modified an evo to take off .060 without any issues....runs like a bat outta he!! too.
I am going to take .030 or so off the heads and put her back together with a .020 screaming eagle gasket and she what she does. It ran good before so this certainly cannot hurt it...I won't have very much compression - using big boyz calculator it comes in at 6.68 right now...it should come up a little bit with the height of the heads reduced by .050 or so.
at least I won't have any problems with Pinging - LOL...
Maybe next winter I will put on some new pistons and go through the bottom end.
What you are describing is the conclusion that I came to over the weekend. The cylinder was bored to 3-5/8" and they put a stroker piston on, but either did not replace the connecting rods or maybe the crankshaft is stock.
Why can't I take that much off the heads? I have read several about several mods that took .080 off - and I personally have modified an evo to take off .060 without any issues....runs like a bat outta he!! too.
I am going to take .030 or so off the heads and put her back together with a .020 screaming eagle gasket and she what she does. It ran good before so this certainly cannot hurt it...I won't have very much compression - using big boyz calculator it comes in at 6.68 right now...it should come up a little bit with the height of the heads reduced by .050 or so.
at least I won't have any problems with Pinging - LOL...
Maybe next winter I will put on some new pistons and go through the bottom end.
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Head Height
I have done some previous cleanup with sandpaper on these heads - to clean the mating faces for gaskets - but they are right at 3.757 inches now...they won't be for very long though. I took .010 off of the last night in a few minutes with a piece of sandpaper.....60 grit - when I get to 3.710 I will go to 100 grit, then 200, then 400 until I hit 3.700".
The jugs - as documented when I trocked and sanded them last time ended up at 5.509" face to face...
Now I need to measure how much stroke I got - er, uh, I mean the bike's crankshaft - so I will know what I have. The cylinder walls have a 3-5/8" diameter....so it is bored, but may or may not be stroked - but I definately have stock jugs and pistons that sit lower on the wristpins than stock - and almost stock heads (except for the porting and polishing that I have done).
Maybe next year I will try to put a stroked crank and such in - but really, she ran pretty good at 6.8:1 static CR - with 90psi at each plug...
If my modifications get me to 7.8:1 and 120ish psi at the plug I will be happy - and she will probably do wheelies - without pounding out 10.5:1 compression.....less beating on that old box the better.
How much increase in static CR and PSI should I see by taking .090 off of the length?
The jugs - as documented when I trocked and sanded them last time ended up at 5.509" face to face...
Now I need to measure how much stroke I got - er, uh, I mean the bike's crankshaft - so I will know what I have. The cylinder walls have a 3-5/8" diameter....so it is bored, but may or may not be stroked - but I definately have stock jugs and pistons that sit lower on the wristpins than stock - and almost stock heads (except for the porting and polishing that I have done).
Maybe next year I will try to put a stroked crank and such in - but really, she ran pretty good at 6.8:1 static CR - with 90psi at each plug...
If my modifications get me to 7.8:1 and 120ish psi at the plug I will be happy - and she will probably do wheelies - without pounding out 10.5:1 compression.....less beating on that old box the better.
How much increase in static CR and PSI should I see by taking .090 off of the length?
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