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

Well in having conversation with a very knowledgeable guy in this hobby he told me that these engines with the cranks marked ZAE50 are the best of the cranks in these engines, they're normally the most true and the best balanced of all of the cranks out there, the engine do require a few tweaks here and there to get lined up properly, but make the best overall engines.

I found the lower of this engine to look excellent and it has one of the better looking pistons that is marked with a # 2 on top with an arrow opposite it on the other side.

What I found I do not like about the particular engine I got is the Jug/cylinder.

It is the worst I have even had as far as the ports are concerned all of the ports are the smallest I have seen on any jug I have ever had, other than that it looks OK, but no way I think this jug could be made into a great performer very easily, it would take a lot of grinding just to get it equal with most of the others I've seen before they had anything done to them, ports are fairly clean but just very small, I know the larger counter weights in these HB engines cause them to have higher crank case pressure/primary compression and that may help force the charge through these small transfers but the intake and exhaust ports being so narrow is going to really limit the rpm potential.

I'm gonna do some work on these just to get them cleaned better and I will likely widen them some and grind a radius in the narrow side corner of the transfers so the air/fuel charge wont be slamming into a blunt surface when it leaves the case headed fro the combustion chamber, maybe that will help it breathe a little better for good mid range power and torque and let it wind up a little better on the top end also.

Pics show what I'm talking about with these tiny ports.

Map

brown said:

Who sells the "half breed" engine?

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The Piston Bike engines are "Half Breed" engines.

I ordered mine off ebay from a vendor in Hong Kong Shipped to my door for $119.00

Thats for the entire engine kit, the jug on this engine is the smallest port jug I've ever seen, but I have other jugs that have bigger better looking ports so I've already just today hogged out the tranfers on another jug and cleaned up the intake and exhaust on it, this jug will go on the engine instead of the one that came on it.

the cylinder jugs can be fou d from several vendors that are better for higher rpms, I wjll use the small port jug on a for sale bike engine after I enlarge them a little and get them smoothed out real nice, they should work fine for a good running well tuned 30-35mph bike with a 36T sprocket and the ports might help make sure the rpms dont get to high and cause the buyer to trash an engine and think they got a bad deal.


Map

Got another email today from and expert builder of these Half Breed engines and he told me straight up that they have the very best crank and balance of all the china girls out here now, he assured me I would be pleasantly surprised and happy with how smooth the engine will run, plus the wider crank counter weights add primary crankcase compression that is higher than what is seen from the other engines which can help increase performance.

Ill find out for myself how good it runs soon, I'll have this engine completely built and running tomorrow if all goes according to plan, still need to notch piston skirt on intake side and put a better wristpin bearing in and she'll be ready to seal up and mount on the bike.

I'll be posting all the initial results when I get this done, I'm hoping this engine will act as Ive been told it should and be a low vibe good running engine.

we shall see.

joelogger2 said:

you need to get the half breed engine from freds cr machine i am totaly impressed about his porting job on them and the addition of the two boost ports

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I do my own port work and it works good for how I want my engines to run.

Fred does do a good job and his stuff from what I see here, and at some point I may get a top end from him for one of my engine lower I have just sitting around.

Thanks for the input joelogger2

Map

well I have good news and a little bad news..

Got the "Half Breed" which I'm gonna start calling a PK-38 since its basically a PK-80 but has the 38mm stroke crank.

Got the engine built, everything seemed to go together just as it should, used the Indian head gasket Shellac on the intake gasket and the jug to case gasket which by the way is the Juicemotoparts solid copper gasket and in this set up is the bad news with the engine.

I suppose the mating surfaces on this engine aren't good enough for the thin solid copper gasket, got the engine on the old Western Flyer bike, and headed out for the maiden voyage, released the clutch lever and in just a few feet she busted off, idle was a little weird but i didn't worry at first, I stopped and wanted to just let it run a couple minutes to warm up and loosen up the new parts and allow everything to get lubricated nicely, then she just kept running better and better and faster and faster.... who can guess what the bad news is here.....?

yep, a dad gum air leak........!!!!!

So tomorrow if I have time I'll pull the jug and yank that freaking copper gasket off and put one of the gaskets I make up and always use without any issues and be done with it.

I will say that the couple minutes it was running it seems that this is gonna be just like Fred had told me it would be and be a very low vibe engine, smooth at high idle a little buzz in the mid rpms and then as the rpms rise it just gets smoother and smoother, If what i seen with it is an indication of how this engine is gonna act when it's cruising down the road, I think this is gonna be a sweet little gal.

I didn't do any piston ramping on this one, I did lower the intake port 1mm and raise the exhaust 1.5mm, I widened the exhaust and intake just a few .001" but nothing major and I notched the piston skirt to fully clear the intake port when it's at TDC, the jug deck is basically left alone accept for running it across some 220 on a plate of glass to skim just a little material off and make sure it was nice and flat.

Port work I did on jug turned out looking real good, I spent most of my time getting the transfers cleaned up to help prevent crazy turbulence and restriction when the fule/air mix shoots into the cylinder, I think it's gonna flow good but I didn't want to get nuts and ruin the lower rpm power.

here is a pic of how it looks sitting on this dirty old bike, got some goop melted of it from spraying carb cleaner around case and jug to see where the leak was, but I'll know more when I get the leak fixed and get a few miles on it.

By the way the exhaust you see on this engine is completely gutted, the flange is port matched as good as possible to the engine port, the stinger has been cut off bottom , the hole drilled out larger and three extra 3/8" holes drilled in the end cap, this bike did just over 50mph with the modified kit pipe with the dax lower I had on it, so this exhaust does breathe good and its not overly loud, not fancy or stylish but it works good.

If I leave it on this bike and engine, I'll probably wrap it in exhaust pipe wrap, the chrome is just a little bright for me on this.

Compression is so low on this "Half Breed" engine so a bit ago I took an extra jug I had and chucked it up in the lathe and removed .060 from the deck, when I have time maybe middle week I will pill jug off of this engine and slide this decked jug on to see what my clearances will be and I think the piston needs a slight ramp on exhaust side since on these engines the piston doesn't completely open the exhaust port when piston is at BDC.

If these mods dont get this engine running like I think it should, I'm gonna probably become a "Half Breed" HT Engine hater.....LOL!

The jug I decked wont be run on this engine, I will just use it for figuring out if .060 is gonna be the magic number to get the piston edge closer to flush with top of jug instead of the piston sitting way down in the hole like it does now.

cannonball2 said:

I think the .060 should be where you want to be. If I am remembering correctly Fred said on his crank ID video that the half breeds piston was about .062 in the hole.

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you're correct, Fred said thats about where it needs to be for the pistonto be at its optimal point in the cylinder.

I know that this engine will not ever even come close to performing like I want it to until I correct this issue.

Theon said:

All 38mm stroke motors benefit from 1mm(.040") to 1.5mm(.060") decking.
As the jugs seem to be made for the 40mm stroke cranks.
I have found, that the 40mm stroke motors, have far better stock port timing because of this.
And as such run great with minimal base gasket.
The 38mm stroke motors, however can benefit from a little more base gasket.
I would be going down to the local 'news agent'/Wallmart, and getting a protractor to use as a timing disc for this one.
As I have found, fine tuning a barrel for a 40mm stroke and a 38mm stroke to be a little different.
I have given away three 38mm stroke cranks, and replaced with 40mm cranks, as this gave me a better motor.
Sure a 38mm stroke may be able to rev a little higher? but at 10500RPM, I pull mine up.

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would you recommend two base gaskets for this set up after I remove the .060 from the deck height.

I know you've tinkered with the 38mm stroke engines alot, I do plan to add a slight ramp on the piston on the exhaust side, do you thunk I could benefit from slight piston ramping on the tranfer areas also.

Im just wanting to help the port timing a little and get the compression up to a medium high but not at a maximum level.

Theon said:

Truly Map,
the jugs I've seen are all different,
This is also why my motors are running the wide inlet jugs now.
If it's a narrow inlet jug, I have no idea what to do to it until I put a timing disc on it.
I have found that a 38mm stroke motor will benefit from a little more base gasket, but my advice is, get a timing disc, get your transfers to what you want, then work from there.
Don't ramp the piston, unless your experimenting and plan to replace it when you get it right.
When your transfers open will determine the characteristics you want to then exploit.
So before decking jug, I take a reading of the transfers, then chose base gasket to suit.
I now know how much to take of deck the jug.
I then get inlet and exhaust to what I want.
One of the biggest mistakes I see here over and over is people giving too much inlet duration to these motors.
Again, this is where I recommend the use of a timing disc.
Also, lifting exhaust, it all depends on what your starting with, I can not make any to the mm recommendations for these motors with out having it in front of me.

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Thanks for the advice and information Theon & Davezilla,

I don't have a clue how to get done what you described, never used a degree wheel and wouldn't have a clue what measurements I should be trying to achieve.

I would like to have this knowledge but knowing what the optimal height of the ports in relation to where the piston is, is something I know nothing about.

I've always read on here where people say the exhaust port normally needs to be raised a little and the intake needs to be lowered about 1mm, I do understand timing is critical and will determine how an engine runs, and I can see how adjusting the base gasket will affect the transfer timing since that will change when the ports start to become open, by increasing spacing between the case and the jug the port timing is advance so that they open quicker as piston travels down the bore to allow a new charge in. this also raises the exhaust port so now I can see why the exhaust port and intake port should be adjusted last and the deck height surfaced for optimal TDC.

Like I said though my knowledge of where the transfer ports need to be is ZERO....LOL I don't have a clue where they should be and it's just a guessing game for me on this part.

Anyone care to expand my knowledge on this I'm all ears...

Thanks again for the reply Theon and Davezilla ya'll got me thinking more on this now....

any more details on what I should be trying to achieve as far as the height of the transfers would be much appreciated.

Thanks