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Post by troutthunter on Nov 7, 2007 10:20:52 GMT -5
I'm building my first perfomance engine and I'm having some issues getting my engine to fall into place. My issue is with the Megacycle 25-162
When I get the timing in at .040" lift at 48deg. btdc I'm getting .000" clearance on the intake valve (checked with clay -crank will still turn through tdc but leaves only a translucent film of clay at the lowest point.)
I assumed that since I installed the suggested wiseco piston(90mm 11:1) and I'm using R+D springs things would be pretty much bolt up. -lol! a hard lesson in the cost of performance!
OK this is what I've done so far:
I got a thicker copper head gasket (.060")
I've dremeled .020" of the intake valve pocket
Now, this still leaves me .020" short of the .060" clearance I want. (.050" is suggested by Megacycle)
I'm considering retarding the timing by 3-5 deg. to give the piston some time to get out of the way.
How will this affect starting/performance? Should I just keep dremeling away another .020" from the valve pocket and go with the suggested timing? Is the piston beefy enough to loose .040" (1mm) and still be reliable?
is there a book I can refer to that (clearly) defines how power bands etc changes according to timing and exhaust header length?
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Post by StewRoss on Nov 8, 2007 3:55:13 GMT -5
Hi, I'd be taking the piston to someone with a mill and having the pockets cut a little deeper. There's no worries taking down to .060" on the Wiseco at all. They've a thick crown. Make sure that you carefully round off any sharp edges on the piston top so as to prevent hot spots forming on the piston and detonation. No short cuts to a performance engine...unless you don't mind bending the odd valve or two...or holeing the crown...heh, heh...I know I've done both. Check the valves on the overlap as well. Moving the timing can result in them becoming 'tangled'...not good. Wiseco's will sometimes fit with no modification with a standard cam, but more than likely not with a higher lift one. The harder springs only control the valves better with the cam. It would be useful to 'degree' the cam as well and do a diagram to see how it conforms to the specs from Megacycle. My Honda one was out a lttle...have you got a multi-holed sprocket that can be 'vernier' adjusted to get the timing just right? My fun will start again soon with my new engine... SR  |
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Post by troutthunter on Nov 8, 2007 9:22:40 GMT -5
I did get the vernier sprocket and I have checked the specs against Megacycle, it looks like it's all as it should be.
When i got the engine it had a bent valve already...very ugly, not somthing Id like to put the engine through again! That's why I'm trying so hard to get the clearance up to .060" I guess I'll get it on a mill this week and re-assembe next weekend. It's been too long though; I'm dyin' to ride it. Controlling my impatience is the most difficult part of this rebuild. I really envy those guys that can work methodicaly and slowly until the last nut is torqued. I haven't even laced up my rear hub and I'm ready to ride!
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Post by colinjay on Nov 8, 2007 20:56:18 GMT -5
Hi,
As Stew said there is not much danger in having the valve pocket in the Wiseco pistion cut a bit deeper in a milling machine.
I have done this to the pistons that I have fitted in my hot SR engine, mainly because I have had the head planed several time to remove blow-by burns from blown head gaskets and warping (with a std head gasket and and 11:1 piston the engine cranks 14.2:1 CR). The biggest problem (and cost) is the time it taked to set up the piston correctly. When I had my first piston done it was by a freindly TAFE teacher who mad up a jig to hold the piston, which still lives in my box of special tools.
CJ
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Post by troutthunter on Dec 3, 2007 14:09:00 GMT -5
Today I finally got it off the lift and kicked it over. I kicked with the ignition off for a while (long enough sweat a little) to get the oil circulating. Then after 3 kicks it came to life! Victory! but the victory was short lived. I have some issue with my carby. I hope you can help me chase it down.
I have a Dellorto PHM 38 pumper. It worked great last year on my SR400 that I rode overseas. I assumed it would have some jetting changes due after the 135cc bump in displacement and the new cam, but this is more than I expected.
It starts very easily with the choke on, but dies instantly when the choke is deactivated. When it starts it has a very high idle that can be dialed down to a 1,200-1,400rpm tickover -but only with the choke on.
My attempts so far:
Checked for vacuum leaks
changed pilot sizes (start @ 53 went down to 49 with minimal reaction seen in the revs)
tried to adjust the slide to be open more in the idle position but that didn't work either.
I have a #60 pilot that I may put in for 5hitz n giggles to see if will enrichen the mix up closer to the choke setting.
I guess we may need to move this discussion to the fuel system forum!
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Post by StewRoss on Dec 4, 2007 5:18:34 GMT -5
Hi, There's a possibility that it may be too lean on the pilot...or the pilot system is partly or mostly blocked. Pull off the bowl ansd make sure it is free flowing. From what I can see the mixture screw adjusts the fuel flow so go to the 60 and see how it performs (if the system isn't blocked). SR |
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Post by caferacercarl on Dec 14, 2007 2:30:23 GMT -5
The Mixture screw on the Dellorto is a fuel screw and is very touchy, winding it out increases the fuel delivered to engine, a quarter of a turn is almost a full point of air/fuel ratio, its worth perservering with, has your carb got a number5 pump ramp? check the bottom of the slide for the number, [ not for idle,but works best in singles] Do what Stew says and clean the circuit first, then maybe try 3 turns out and adjust from there. regards Carl
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