Got my new "Half Breed" Engine apart and I found...

[mapbike]

Thank you very much Theon, yes a little time needed for ironing this procedure out but I know now what I need to be shooting for.

this reminds me of the changes that just a few degrees of timing change makes on 4 stroke engines, to advance a few degrees helps low end power and then to retard a few degrees sacrifices a bit of the low end but I increases power in the upper rpms.

since I dont use reeds I guess 123-124 degrees is what Im gonna be shooting for then once I get me a set up to do the job put together.

Thanks again for the great info. hopefully this will help others also.

Map

Dave uses a dial gauge to get TDC, I use a squish test, which can be more fiddly, but will give a reasonably accurate result with patience.
I use a very thin base gasket at this stage to minimize error through compression of gasket, or leave base gasket out and tension barrel/head down with again no gasket or if barrel has already been decked, appropriate gasket to get me under a mm(>.040") of squish (.020" is perfect), I then use a piece 1mm solder and find the point at which the crank will rock back and forth against the pressure of the solder. You should find it will 'bounce' approx. 3 or 4 deg. Halve this, and you have TDC.
Set your Disc (attached to crank on the Mag side works for me, but drive gear side is OK also). Make sure it can not move on the crank and set pointer to suit.
Now you should be able to work out where your ports are opening.
I lift the head, and retention the barrel so I can better see whats going on.
Transfer timing is best kept close to 120 deg duration, even a little less, depending what your after.
So, the transfer port should be opening at between 119 deg ATDC and 124 deg ATDC.
119 giving Top end, 124 giving low down.
I usually aim for Top End and let the reeds help the low down, so 120 I find good.
But without reeds, and for a good bottom end, I'd go for 123 deg.
As you have probably gathered, 3 deg is a rather small amount, and likely equates to about a difference in base gasket of around 1.5mm?
But without going to this trouble, It can be very Hit and Miss.
The other beauty of this effort however is the ability to accurately duplicate good results.

 

[Davezilla]

Yes... Theon and I do things slightly different but there are more ways to get to the same place than one... and most of them work just fine.
for me, when I set the squish, the base gasket stackup is installed then spacers are added above the jug so I can torque the jug down. I use solid copper gaskets in both places so the torquing won't crush the copper and the results are dead on everytime. For a paper gasket, you can measure the thickness of an old gasket or use one for setting things up then replace with a new one when done since they're fairly cheap.
Once I got my bottom end set up I'll attach the degree wheel and pointer, then I'll zero the wheel first by tightening it down but loose enough to be moved a little if bumped, same for the pointer, then I mount the dial indicator and pre load it by about .1" and bring the piston up to TDC, next I'll zero the dial indicator to TDC, checking it several times to be sure. You can rock the crank about 3 degrees in either direction before the piston actually goes down but I always check this since a little more or a little less stroke will change this even.
Once I know exatly where TDC is at, then I move the pointer to zero on the degree wheel and lock it down, I'll also lock the wheel so it can't slip, then double check that it didn't slip while locking it down... Now I'm ready to take a few measurements...
my method is pretty tedious but it's accurate to less than a degree, also, I keep the pointer as close to the wheel as I can without tuching the wheel so I don't read it wrong because I'm not looking at it exactly straight on as well... just another tip to increase accuracy.
The gasket stackup at the base does more than just the squish for me because it does effect where a port opens or closes in quite a few degrees just by raising or lowering a few thousandths, this is why the different thickness gaskets Juice sells are so appealing to me.

I finally found my specs for the jug I'm currently using, at least how much was milled off the top and the bottom, and the port durations. Theon may remember when I transfered the jug to the Dax bottom end and the piston came up about a milimeter past the jug deck, but to correct this I made a .040" thick spacer to put the top of the piston level with the jug, or at least close to it, Then I torqued the head on and set the squish, it came out to be too much room in there so I cut off more from the top of the jug and ended up cutting a total of .052" on top with another .040" at the bottom.
After the spacer was made, this effected my port duration by about 12 degrees and what I ended up with was 167 degrees exhaust, 132 degrees intake, and 130 at the transfers, I was able to get the squish to come in at .75mm (.030") this is also a bit further than I or most others were comfortable with, but for some reason the engine still makes good power down low, and it can still rev to about 9500 rpm on top at top speed, it can also idle rediculously slow if I set it that low, but I keep the idle around 1000 rpm for easy pull starts. The bike pulls very smoothly and progressively stronger as the rpm goes up and it's really strong from about 25 mph all the way to 42 mph which is the fastest it's gone so far. The way the engine is set up with the long port durations this one can make more power on top with a bigger carb (I'm running a stock NT at the moment), but with the bigger carb some of those ill effects of the longer durations may be more noticeable, but this can be prevented somewhat by rolling into the throttle instead of just gunning it to full.
I'm still looking for what I did with the paper I wrote down my port opening and closing events on but if I don't find it I can find the events again by removing the head and putting the degree wheel back on.
The easiest way to calculate port durations I found is to measure your port open time in degrees, then subtract that number from 180, then multiply by 2 ... there are other formulas out there that may be more accurate, but this one is really close.

 

[Davezilla]

Yup... 123 to 124 degrees on the intake will do really nice... mine's 132, but because I didn't want to start over before testing how it ran, normally I wouldn't go that far intentionally on a piston port engine, but I somehow got lucky.. then if you ever add reeds, just cut a hole or series of holes in your piston to make a window for a full 180 degrees... then we get to go into boost porting 101 to find even more "hidden" power.

 

[Theon]

Choosing port timing is the same as choosing a cam for your Chevy,
Some want a 'Lumpy' Cam, some want it to be more 'Drivable'.
Neither is right or wrong.
But you want those numbers to mean something, not be a stab in the dark.

 

[Theon]

I first started reading Phil Irving as a teenager, My Father got me 'Tuning for Speed' and 'Scientific Design Principles of Exhaust and Inlet Systems', as gifts in my early teens. Growing up in a mechanic shop, I had a fair idea what he was talking about, but a lot went over my head.
You may find the same with Gordon Jennings and 'Jaguar', but if you reread it, and ask a few questions, Do a few experiments, it will all become clear.
This truly is the best way to understand what your trying to grasp.
I found a blend of Gordon's and Jaguars Advice very helpful.

 

[Davezilla]

Yup... that's pretty much the same way I explain it.... its like adding a hot cam to your car... not enough cam and it don't make the power or rpm you're looking for and too much cam will make the power on top but make the car very sluggish and boggy in the rpm range you drive in. A few degrees over wont hurt if you can build the rest of the engine or car up enough to support it either by lower gearing, more compression, and the right size intake and exhaust.
Also on that note, the whole engine must match the porting or cam or you'll end up with a poor performer. Since I knew my duration was on the high side but not so high that it would ruin the performance. It just needed to be compensated for by changing a few other parameters. I did compensate for it by building the rest of the engine around the port timing and duration. The compression ratio is as high as I could make it and still run 93 octane, I kept the 44 tooth gearing, and tuned thenpipe to match the engine by adding a 4"long section to the belly of the pipe. The KTM pipe also has the right baffle shape to widen the powerband a little more, but every little bit helped.
If I was off by like 20 degrees tho I probably would have been better off starting over with a new jug because the other mods would have not been effective enough.
I've seen too many people put too much cam in a car or the wrong intake manifold then wonder why its slower.
these engines can take quite a bit of duration but above a certain point it'll lose it's "street" manners and wont be as practical or fun for everyday use.

 

[Davezilla]

I also fully agree about following Gordon's advise in his book as well as Grahm Bell's and Jaguar also has some really good stuff too. As far as I know, his torque pipe is one of the best ones out there, the reason we don't see them very often is because they cant be bought,but built from the plans on his site.
Pipes tho can also make Angkor engine into a great engine when tuned and shaped right, but can offer little or no help, or even take away performance if not designed right or tuned to match the engine.

 

[Theon]

What I gathered, Gordon wanted 12 000 RPM, Jag wanted 8 000 RPM, I want 10 000.
So somewhere in between is what I aim for.

 

[mapbike]

excellent thread for information this is becoming, much of it is beyond what I have done to another of my engines and as I have told Dave, I suppose with some of my mods I've just been fortunate enough to get somethings close enough that I ended up with fairly good performance, the highes rpm I've ever recorded on one of my engines was 9,400 the thing sou ded like it was going to fly apart...lol

This was not running on flat ground but going down a slight decline so the load was less than a flat land run speedo was bounce off 48-49 mph and to be honest Im not sure the tach I had was 100% correct so maybe I wasn't actually turning 9400 rpm the bike had a 36T and 26" wheel I was being followed by a motorcycle and I was told that his speedo was right at 50 mph and he wasnt gaining on me so I'm pretty sure my speedo was right.

I really don't care to have a max speed over 45 mph so I can cruise comfotably at 33-40 mph most of the time.

Im anxious to get my stuff together and gets cracking with one of my dax lowers, ive decided I don't want to get this in-depth on the hybrid "half breed" engine since it's balance isnt as good as the dax lowers I have, they run a lot smoother from low all the way to max rpms and that is the foundation I want to work with and not one that has a real buzzy med rpm range like this 38mm stroke "pk38" as I've started calling it.

very good explanation fellas this is gonna help me get the engine where I want it to be, Ive been wanting to do this for a while because Im tired of the guessing game and never knowing for sure what Im gonna have when I get the engine together.

map

 

[cannonball2]

I will just throw this in the middle here. This is a pic of the half breed crank and a Dax crank. The 1/2 breed is quite a stuffer. Both have a similar rod design relating to oiling holes/slots. The Dax is somewhat more finely machined with what appears to be thrust type washers between the rod and crank halves leaving zero side play that is evident in the 1/2B rod. Its also advertised as 40mm stroke. If I had to choose based on manufacturing appearance it would be the Dax. Doesn't mean the 12/B crank isn't good. Why cant you run the GT 5 jug? its 38mm on stroke.

I have read the Jaguar site almost completely. Theres a lot of good info there and it benefits from being up to date conceptually from the older
"Bibles" written in the 70s, not that physics changes but more fully understanding them do. I believe it all works together to understand the simpliest most complicated engine design in the world. The Jag site is worth a read. Theres also a good explanation for retarding timing at very high rpms.

 

[cannonball2]

Another side note, I just bought this kit for $99 shipped. I could have bought a completed engine for the same or maybe less. I gladly paid the price to not have to disassemble to it find some ones mistakes. Heaven only knows if I will get the same as whats in the pic, but if I do then it appears to be a 1/2B crank engine. Will build for longevity adding high end bearings(probably SKF and a Japanese pin bearing). All I want is a smooth reliable engine. Will have to decide which crank to use. Race Engine-wow!

 

[mapbike]

yep cb2

I have a dax crank and a Half Breed crank also and the lower bearing on the HB crank is a little rough and stiff, the rank I got from dax is bed smooth and the ma hine work looks a little better than it is on the HB crank.

you mentioned using a GT5 Jug, I haven't tried it yet but it made be possible as long as the typeB piston was used, I know the GT5 jug wont work with the piston the HB engine comes with because they normally use the type A piston.

Fred told me that the standard type A jug can be used on a GT5 engines long as about .100" is milled off, this main not work on all jugs though since I have some jugs that dont have enough material between top cooling fin and top of deck to allow .100" to be removed without milling about .040" off the op cooling fin.

I suppose one could remove some from the bottom of the jug and then use mutiple gaskets to get jellyg so piston is just a hair shy of being flush with deck, butter thats is gonna jack the time up doing it that way.

I have a GT5 jug I plan to clean the ports up on and use on the GT5 lower I got from YILDS.

what Im gonna do to this HB engine is use two base gaskets and then set jug deck to give optimal compression since the way it is now makes compression very low.
If my thinking is right this will retard intake timing a little and advance the tranfer and exhaust timing a little, Im thinking this along with the increased compression will add alittle more power overall and especially help in the higher rpms to possibly get this engine over the hump alittle, this HB engine isnt balance as good as I was told it would be, maybe I just got one that isnt an example of the majority, I dont know since ive only had this one, once I get it to pull higher rpms I'll know more of what it is and may actually like this engine better pulling lower gear ratio since it gets smoother the higher it winds up.

I can guess about it all data and never know for sure, so I plan to do the mods and see what I end up with, Im not gonna get serious with this one since the crank balance is a little more off than I like but I will try to get it running better than it does now so if I do sell this engine on a bike the buyer will get a better than normal engine.

I'll play with it a little more before I decide what to do with it.

 

[mapbike]

Another side note, I just bought this kit for $99 shipped. I could have bought a completed engine for the same or maybe less. I gladly paid the price to not have to disassemble to it find some ones mistakes. Heaven only knows if I will get the same as whats in the pic, but if I do then it appears to be a 1/2B crank engine. Will build for longevity adding high end bearings(probably SKF and a Japanese pin bearing). All I want is a smooth reliable engine. Will have to decide which crank to use. Race Engine-wow!

Im thinking those are GT5 engines but I could be wrong, whenbyou have the crank in hand you'll know for sure and of course the piston will be the quickest identifier, wrist pin in the middle and bingo.... GT5, Type A piston and crank marked ZAE50 and you have a Half Breed.

be sure and let me know which it is, Im curious.

 

[Davezilla]

yep cb2

I suppose one could remove some from the bottom of the jug and then use mutiple gaskets to get jellyg so piston is just a hair shy of being flush with deck, butter thats is gonna jack the time up doing it that way.

On something like this, cutting on the top of the jug to get the piston closer to the deck or even with the deck is acceptable, but cutting on the bottom of the jug will change the timing the same way removing the gasket to lower the jug would since it effectively lowers the ports in relation to the crank.

Basically, anything you do to the bottom of the jug, cutting, adding gaskets, or changing gasket thickness, will all effect the timing. This can be a good thing tho if you're desigining a torque engine, but if you're shooting for high rpm power not so good and any cuts made to the bottom would have to be compensated for by shimming. Like on mine I cut .040" off the bottom to get it flat and true, but went back in and added a .040" thick aluminum spacer sandwitched by a .025" and a .016" copper gasket so all in all even after cutting the bottom, the jug ended up raised by .041" in reference to the case.

You can shim the bottom by either doubling up on base gaskets, making a shim, or stacking copper gaskets. Personally if I was using paper gaskets only I wouldn't go more than 2 gaskets thick, but with metal gaskets you can get away with stacking a few more. I've also had to trim the metal gaskets to match the transfer openings, the ones Juice sells match fairly close but he does leave enough metal for the end user to "trim to fit". His head gaskets are spot on tho.

 

[cannonball2]

Ok Im trying to understand whats going on here. The 1/2B crank has a 110mm rod+ about .3mm, the Dax rod is 110+about .6mm for a .3mm difference in the overall length(not pin distance). Dax says his crank is a 40mm stroke with a 115 rod. Whats he talking about? In theory the piston would be way out of the jug.

Maybe this will help other folks like me trying to arrive at a good crank/piston/jug combo. https://www.youtube.com/watch?v=rzLWYSlpFEg

 

[Davezilla]

Different type of engine... some of them have a longer rod and higher piston pin hight so they sit about the same in the cylinder.
I had one that the piston stuck out above the deck by 1mm but to fix it I made a shim for the bottom of the jug since I needed to raise the ports anyway. If I needed to keep the ports low it could have been corrected by using a thicker head gasket or stacking 2 gaskets on the top. You can also get thinner copper gaskets for the head and base to give even more hight control when needed like setting up a tight squish clearance.