sicivicdude

SO we all have these recommendations about "squish" or "quench" areas but there seems to be quite a lot of speculation or guesstimation going on about what's the "right" amount and why. The rule of thumb is as follows: on a trail motor .050" between the piston crown and TDC and the surface of the head squish area is "about right" but why? First, lets get into MSV. What we're talking about is Maximum Squish Velocity and it equates to the fastest you can push fuel laden air before you excite it enough to explode on its own. Think about it, fuel and air mixed is a bomb waiting for a hair trigger (the spark plug usually) but pushing it fast enough causes enough molecules to slam together for the ignition to start on its own from friction. The latest and greatest head design (designed around MSV) results in a small hemispherical combustion chamber centered around the are you WANT to detonate (the spark plug) and tight enough tolerances out away from that to dampen the fire but not SO tight that it ignites the fire itself. When I say dampen, I mean that the "squish" or "quench" area is designed NOT to burn so that the charge is centered inside the combustion chamber and right around the spark plug. So let's walk through a combustion cycle in a MSV designed head..... It all starts when the transfer ports close (piston coming up) and the volume inside the cylinder is either rushing back in the exhaust port or trapped back inside the combustion chamber already. As the exhaust wave pulse from the tuned pipe does it's job, it rams the charge that has escaped out through the exhaust port back into the port right as the piston closes the exhaust port. This has a mild super charging effect in that the pressure inside the chamber before any piston led compression has taken place is already above ambient (14.7psi at sea level). As the piston rises (in the area above the exhaust port) the charge is being compressed. We have homogenized fuel and air (mixed) that is being pushed upwards as the piston rises. This is creating local hot spots (the reason why carbon on the crown is important!) but overall the charge is only gaining pressure and heat as a square of one another. As the piston gets near the top of the stroke, the fuel and air around the outside spikes in temperature and pressure locally as it's pushed between the piston and quench area. This action is the beginning of the REALLY hot charge as the speed of the engine and size of the squish area determine exactly how fast the charge gets pushed in this part of the stroke. It's VERY important not to push the charge too fast during this part, Remember, that charge is a powderkeg at this point and ANYTHING could set it off. Now here's where the magic of MSV heads really comes to shine.... at a certain point (assuming the charge was never pushed "over the edge" and predetonated) the piston rises close enough to the head surface that combustion actually CANNOT take place. This is the reason why this head design has two different names, squish and quench. One describes the action of pushing the charge towards the spark plug, the other describes what happens at TDC (and the spark event more or less). Once the clearance between the head and piston gets close enough, (generally that sweet spot of .050") the charge is pushed out hard enough that it becomes non uniform inside the chamber. The areas around the outside are no longer suitable for combustion. Also, because there is only a thin layer of charge between two pieces of relatively cool aluminum, more heat is drawn out of the charge (cooling by the head and piston) than is being put in (pushing upwards by the piston). Once that occurs, it's called "dampening" of the fire out in the squish area. Then it brings us to the ignition event. What we all came for.... The spark plug fires and all that fresh charge that was just pushed in towards the spark plug all explodes with the fireball growing out away from the electrode of the spark plug as a flame front. This flame front pushes out and down as the pressure rises exponentially pushing down on the piston and crank (and out eventually towards the wheels!). As the flame reaches the edge of the hemispherical bowl shaped combustion chamber, it has to "roll" out around the edge of the squish area. This is why the "break" or edge angle is actually fairly important.....[

While it may appear that way to being with, I promise you it's not ALL like that. That entire subject however, is a topic for another thread or maybe not on here at all as it's not my desire or attempt to drag BHQ and BF into another spat! I simply had some banshee related work I did recently and figured I'd post it on the most relevant forum available.

There, I fixed it for you Maybe some day sir I will but I have to get there first. What you are seeing in the pictures at the beginning of this thread is the start (not specifically that head ) for me.

While Ken (and/or his disiciples) are amongst you, I am NOT one of them. Surfrjag an ddq have met me personally and can attest to that. @ wheelman: AWESOME! That's the bee's knee's there.

I appreciate your kind words at the beginning and any advice you may have to offer. I will also think critically about anything said and try to find the "gems" in it. Obviously, not everyone who's ever done anything has done it in a 5 million dollar machine shop (not specific numbers, just saying). Some people truly do have to start "somewhere" and you are looking at that "somewhere". Any other advice you'd like to offer besides "don't do it"? Someone else suggested moving the bit down and into the fly cutter quite a bit more and "boxing it" in to reduce flex. I'm going to try a different carbide insert in it too, instead of the 60° pointed one. I've seen every different kind of fly cutter/head surfacing contraption you could name in my research. There's this really trick one made out of a SBC cast iron flywheel with many cutting bits spread around it. I decided for simplicity in the single point setup and may pay for rigidity for going the "easy" way. Do you have any suggestions as far as modifications go to that setup specifically? I was doing .010" fly cuts to reduce the mating surface down to where I wanted and even during the process the bit, flycutter, machine, head, and jig were not only not moving but only making a tiny "whoosh" sound as it was parting off metal (no chattering, no vibrations, nothing) so I think I'm on the right path there. I finished this up with a .002" finish cut (but again using the 60° pointed cutter) and then lapped the tiny ridges off. The lapping process was smooth all the way across the head (grooves were removed evenly during the process) so there's not that much variation across the surface. While I did just "branch out" into doing banshee work, this wasn't exactly a blind experiment either. I have been doing yamaha blaster heads for a while and have that pretty well down pat.

What I meant by that statement is that the idea behind the work is the same, he has REALLY good photographs on his website.

No misinformation exactly, but I'm sure cast in the worst possible light. I've ruffled as many feathers there as I undoubtedly will here so I have a "fan club" as you might call it. I learn by doing. With that comes mis-steps. Those mis-steps can either haunt or empower you. I choose to let them empower me to do better next time.

None of these I've run across have had that issue but I have seen blaster heads (what I have a LOT more experience with mainly because my old lathe didn't have enough swing over the bed to turn a banshee head!) with that issue. Seems yamaha wasn't terribly accurate in their machining processes. I certainly will be on the lookout for that issue before I throw one into the machine. Any other nuggets of wisdom you'd like to impart (not being a smartass here, actually asking for any other information you could bestow)

LOL This certainly isn't for everyone. The particular head setup is for someone who values that stock look.

I mispelled Haas, sorry. Their machining centers are a HECK of a lot nicer than anything I have or have access to. I'd be happy with a Chevy considering I'm riding a bicycle at the moment! For the record, I didn't know you (or anyone) did this work in particular. The head pictured is one I was given for freebies and decided to "play" with to help out a buddy. I didn't go about advertising this to begin with.... Read back through the thread. Someone else asking how much so I answered. I wouldn't blame anyone for going with someone else, just figured I'd throw my lot in the hat. I do appreciate your kind words and would be willing to listen to a few rocks (gently thrown mind you) as I try to learn everything I can. Thanks everyone for the attention. Matt, everyone who feeds you sugar isn't your friend. Be careful what you read from that "anonymous" member you got a PM from.

I'm not "from" blasterforum any more than you are "from" BHQ. I am a member on both as well as E2S. I'm not the one calling myself a machinst, read back through the thread. I simply posted the work I had done. I'm also not believing that someone with a 18mm DM engine is going to try and run a stock rechambered head. Only pointing out that stock heads have a lot of potential in them without running a pro design head. Good upgrade for a regular trail banshee.

That is the thread where I got the new machine. It's not exactly like I tried to hide who I am or what I do. I used the same screen name here as there.

And that has...... what to do with this thread? It's a indexable carbide insert tool with chip breaking edges as pictured.

I figured you were watching blasterforum too when you said something about 6 weeks. That doesn't count any of the time with my lathe prior to that or any of the machining work I did before I got machines at home.

Some of the best work I've ever seen has come from "some dude in his garage".... Who said anything about 6 weeks?

I slowed it down with a carbide chip breaker tool bit installed. It still left tiny ridges from the forward feed which I felt the need to lap off. Would it have worked well without the lapping? Probably. Is it as smooth now as the lapping stone? Definitely!

That's a 13 x 40 Smithy Granite with .0005" z-axis DRO and .0001" X and Y. While it's certainly not a Hass 5 axis CNC machine, it is more than adequate for the work being done. What milling machine do you have? Any pictures?

My point is that this is not a carbon copy of another design. This is special cut for a particular application. The combustion chambers are redesigned and polished and the mating surface flycut to correct the squish gap thickness.

Misunderstanding. What I meant was that this is a rechambered stock head cut to the owners need. It's designed using a computer program to calculate the squish velocity. I did not buy someone's head and simply copy it.

Because everyone has to start somewhere. They were amateurs at one point (10 years ago by his own words apparently) and had to overcome the exact same resistance. I'm sure Willard appreciates your vote of confidence.

I was referring to the picture with the background cut out of it and the polishing with a nice backlighting. Looks GREAT btw.

That was the first one I did and the one I used to make both my jigs for doing the work! One for the chambers, one for the face milling. Not much one for just sending out any old crap either. Like, going the extra mile and lapping the mating surface to make SURE it isn't going to leak. Glad I went the extra mile? Anyone who might be interested can PM me. I'd be more than happy to discuss anyone's particular needs.

It actually started out as a stock good looking head. I spun it around and polished the hemispherical combustion chambers. I then removed approximately .025" from the squish area to "sharpen" the break area some (keep that charge speed up!) and correct the overal diameter of the combustion chamber (66.5mm OAD was the goal). Once that was done, I fly cut the mating surface down to correct the squish gap and finish lapped it to spec. If everything adds up like it did in my calculator, you should have .049" squish gap and a 21cc head for a cranking compression of 155psi. Let's hope I got it right the first try.... I was wondering who surfrjag traded that to and if I'd ever hear back a ride report. He sent me those 17cc domes to take a look at too!

What you are looking at is the same thing with less photoshopping Maybe. I have 3 cores right now (none as bad as that one) that I'll be running on but I might take you up on that offer if some people are interested in getting their heads modded.

I built a flycutter for doing it but it leaves thousands of tiny ridges. The bit moves along under power feed and as it moves forward, it leaves a cut surface behind it. Some people might trust that, but I take it a step further and finish lap it. Are you complaining about another step someone is willing to take to ensure a leak free installation? $96 for pump gas heads and $116 for big bore and stroker mods from that other place. Sounds about right for the level of effort needed to complete the job and right in line with what I figured. I lumped all of them together in saying $120 no matter the need for modification.