| Author | Message | ||
     Sportyeric |
How important is it? I've started on the project with Thunderstorm heads. The 15 degree shelf is not very accurately cast so I've had it machined accurate. The down side is that the shelf as cast has a bit of a step down before the sloped shelf begins. Now the step is about 15 thou. Starting from that point, I'm probably going to need to shave either the head or the cylinders to the point that I'll need adjustable pushrods, which are an added expense that I'd rather not spring for. I'm considering just scrapping the squish plan. What do you think its worth in terms of power and pinging? Alternately, how much free play do the lifters really need? If I take 40 thou off the cylinders (or whatever is needed once I measure it), if the stock pushrods still provide 15 thou clearance before bottoming the lifters out, that should be enough to allow for valve seat recession, yes? The lifter slack is more for expansion of the cylinder than compression of the valve line. | ||
| Sportyeric |
Nobody is answering you, Sportyeric, because you should have searched the archives first. This has already been discussed several years ago. In fact, you were part of the discussion. Too many brain cells killed over the years. It seems the correct answer is: Squish is important. Decking to 50 thou seems to be OK. New news. There are Screamin' Eagle pushrods that are 50 thou shorter than stock, made just for these occasions. New question. At what point in decking for correct squish will I have issues with intake manifold fit? And is the fix as simple as hitting the manifold with a belt sander or is it theridge above that becomes an issue? | ||
| Sportyeric |
Another question, since its so fruitful asking them here. It looks like I might need to deck the heads 50 thou or more for proper squish. Still haven't measured. At what point will valve to piston clearance become a problem? I'll probably have to measure that myself anyway but is it even close? Need I bother? (Its extra work to re and re the valves for the mearing.) | ||
| Woody1 |
Glidden often told people that the reason he dominates his brackets was that most people spend 2 weeks building an engine but he would spend 2 months building an engine. My experience with engine building is that it is hard to beat the guy who addresses the details, to me squish area is critical why spend the time and money on everything else and then screw it up cutting a corner? to get it right you may need to shave the deck and/or dish the pistons I'm sure the heads will need to be shaved to compensate for the machine work that has been done. but ultimately most engine builds are reverse engineered for desired results and then the decisions are made from there to get the proper fit and finish | ||
| Sportyeric |
AWW!!!. I just measured the piston-to-head clearance and its 90thou!! With the heads already decked 15thou. I wish I had never started messing with it. Or that I'd taken them to someone who understood what I was after. In hindsight, I should have suffered the inaccuracies of the cast 15 degree shelf and tried for a good squish out of that than to have it machined to accuracy and give up any possibility of getting it close at all. I'm pretty sure that decking it another 55 thou to get a 35 thou squish is going to give me valve clearance issues on top of the need for shorter pushrods. Thanks for your input, Woody. I'm starting to consider what the use of the bike is. My Sportster is for roadracing and maybe the drag strip while the Buell is my two-up tourer. It would still be nice to put up a fight with the Ninjas if and when I'm solo but the project is failing. I think I'll deck another 35 thou to a total of .050, keep the stock pushods, and leave the squish non-existant at .055. Whooops. Just did the math and that would leave me short 9cc of chamber volume I think. I'm going to bed! (Message edited by Sportyeric on May 05, 2009) | ||
| Mtkawboy |
Cutting the head will have no effect on quench or total deck clearance. You have to do it with gaskets or cutting the cyl base or top or a combination of all three. Quench is the area between the top of the piston & the head so cutting the head does nothing except increase compression | ||
| Queenofspeed |
mtkawboy, Actually that is not true when it comes to thunderstorm heads as they have a shelf between the deck and where the 15 degree squish band starts. To get the proper squish you need to deck the heads down to where the 15 degree starts so that you eliminate that shelf. On other heads such as XBs what you said is true but not on lightning or thunderstorm heads. To do it right it is best to have a professional shop with a CNC machine do it so it is exact | ||
| Pash |
Has anyone measured the angle of the squish band on the piston? I was always led to believe the Thunderstorm heads and pistons were matched, however: The head has a poorly cast 15 deg squish band:  But when I look at the piston (part number 22546-98YA which comes as part of kit 22676-98Y):    The squish band is 10 deg... These parts are out of a 2002 X1. | ||
| Buelliedan |
that is correct. Stock thunderstorm pistons are 10 degrees but the heads are 15 degrees. NRHS has true 15 degree forged pistons if you want it to match up correctly. | ||
| Pash |
Many thanks for responding... | ||
| Nitrous_jim |
from my experience the tighter you get it the more it will resist pinging. I have set motors at .018. (I am not saying things wont hit if you try it) when I first got my buell I took it apart and cut a total of .055 from the heads and cylinder surfaces and still ran the stock pushrods. I have also used J&E 30 degree pistons as a starting point. put them in the lathe and cut them back to 20 degrees, then cut the chambers to match. the first time I did my buell I cut out .055 to bring the compression to 11.4. swapped out the cams for some andrews n6's and it made 103 hp on the dyno. custom exhaust, carb mods, and ign. the tool you are using to measure your piston dome is not accurate enough. IMO. you need a good protractor. this one reads out to one tenth of one degree. bad pic but you can see it.  one way would be cut the cylinders so yo have zero deck. then when you have your heads cut right the quench will be determined by head gasket thickness. (Message edited by nitrous_jim on February 20, 2013) |
