DIY guy went HT Motorized Bicycle

Agreen · Jan 25, 2014

Finally bought a China girl engine last week to see what all the fuss was about. I love this thing! I'm especially fond of this thing's clutch. I'm thoroughly impressed with it altogether, even if it was made in China. Kind of confused me a little when I didn't get a fortune cookie in the box though.

So far I have about 8.5 miles on it, but I'm already running in to issues.

It only gets up to 30 mph max, and that's after being wot on a flat road for a long long time. It has the 44t rear sprocket, standard 66cc 2 stroke kit with an NT carburetor. I've set the needle at the 2nd notch from the top after finding it close to the bottom. Before that it would bog down on throttle transition from idle, so I tinkered with the position of the clip and found the 2nd from the top was the best place for throttle response. Not sure if 30 is normal, but from what I was seeing with others and the 44t sprocket that they were getting closer to 40 mph.

The carb doesn't fit. I had to rig a temporary intake made from heater hose and 1/2" pipe until I can make a decent manifold for it. No air leaks from this set up, but I don't expect the heater hose to last very long.

Most importantly, the chain stays are getting eaten up from the chain. I've seen where some people stretch this area, but my frame looks like it can't be stretched in that spot because of the rear brake. Maybe you guys can shed some light on this one on what I can do. I'm an experienced welder, so fixing that chewed spot won't be an issue, but I'd like to know what I can do to prevent it from happening again.

Thanks for looking!
Terrence

And my other "motorized bike"

xseler · Jan 25, 2014

Re: DIY guy went HT

Be careful with the WOT while it's that 'fresh'. You could substantially reduce the life of the engine. A 36 tooth sprocket may lower the height enough that the chain will clear the stay.

Best of luck with your project!

Agreen · Jan 25, 2014

Re: DIY guy went HT

Ah yes, the break in period. I'm well aware of it. I did let it sit and run at a high idle in my driveway for 3 separate half-hour sessions, so it should be pretty close to broken in by now. Just trying to get a feel for it and make sure everything is tuned in properly. I essentially have to go wot to get barely faster-than-pedal speed though. It seriously takes a long time to get it up there!

I just went out an re gapped my spark plug after finding the spec finally (0.025", in case anyone was wondering). The gap was right around .020. So I went out for a test ride and it felt even more sluggish. I took the breather off to see if it's an intake restriction issue and gave it a couple of throttle blips. Each time I did I got misted by raw fuel coming out of the carb's inlet. Either China timed the ports wrong and I have some porting to do, or there's an issue with my carb that has no adjustment...

Theon · Jan 25, 2014

Re: DIY guy went HT

You'd be pretty lucky if China got you port timing right!
I was taught to use an engine through it's expected rev range while breaking it in, just try not to get it too hot ( holding WOT for extended periods).
36t sprocket will possibly be to tall unless your on flat ground and have tuned the motor properly.
I have slotted the rag joint rubbers with 1mm cutting disc on one of my bikes to get the sprocket closer to the wheel, but how is your sprocket alignment? I find it is usually a little 'wide' on a multi speed with rag joint. 39t sprocket is usually the go with 26" wheels, and with a well preforming motor should get you to at least 60 Kph. 40 Mph with a 44t is getting up in the revs, probably not from an 'untuned' motor.
Can the front mount be made to sit lower, I usually shape the front opening and if I have to give the frame a squeeze to get it to mount, also shorten rear spacer block.
On the Phantom I left rear block out and shaped the cases a little to match the sharper frame angle sharing the angle difference from front and back.

2door · Jan 25, 2014

Re: DIY guy went HT

If I may I'd like to offer you some advice.
You really need to look at your chain alignment and see if you can move that rear sprocket inboard a little. The chain eating into the frame like it is will cause you some problems. Chain and/or frame failure aren't good things.

Letting an air cooled engine sit and run isn't a good idea. Air cooled, means it relys on air moving over the cylinder and cylinder head cooling fins to dissipate heat. You aren't doing your engine any favors by that method of break in. Ride it, or at least put a big fan in front to move air while it is running.

2 stroke, piston ported engine will 'spit back' through the carburetor. It's just the nature of the beast. The air filter/cleaner will absorb a lot of the blow back but not all. You'll always find the filter element oil soaked. Nothing you do will change that.
As far as break in; we always suggest 200 to 300 miles before starting to look at modifications or performance upgrades. And then do only one at a time so you have some comparison.

As far as your speed? 30mph is very respectful. Those 40 claims are often just that, claims. If you are reaching 30 with a 44T sprocket and a new engine, you are a lucky man. Don't change anything and see where you are after that 200 mile mark.

Good luck.

Tom

maniac57 · Jan 25, 2014

Re: DIY guy went HT

2door said:
If I may I'd like to offer you some advice.
You really need to look at your chain alignment and see if you can move that rear sprocket inboard a little. The chain eating into the frame like it is will cause you some problems. Chain and/or frame failure aren't good things.

Letting an air cooled engine sit and run isn't a good idea. Air cooled, means it relys on air moving over the cylinder and cylinder head cooling fins to dissipate heat. You aren't doing your engine any favors by that method of break in. Ride it, or at least put a big fan in front to move air while it is running.

2 stroke, piston ported engine will 'spit back' through the carburetor. It's just the nature of the beast. The air filter/cleaner will absorb a lot of the blow back but not all. You'll always find the filter element oil soaked. Nothing you do will change that.
As far as break in; we always suggest 200 to 300 miles before starting to look at modifications or performance upgrades. And then do only one at a time so you have some comparison.

As far as your speed? 30mph is very respectful. Those 40 claims are often just that, claims. If you are reaching 30 with a 44T sprocket and a new engine, you are a lucky man. Don't change anything and see where you are after that 200 mile mark.

Good luck.

Tom

2door covered it really well. Your motor is doing just fine for such low mileage. I find most of my builds take at LEAST three or four full tanks of RIDING to break in fully. Idling it in your drive way does NOT break it in like riding it.
Swap to a 36 tooth rear and a good midrange tuned pipe once it settles in and you will see 35-40 mph easily.

You can easily spread your rear framestay for chain clearance. Just use a cheap import car screw jack and some boards to spread the load so the tube does not kink. You may need to re-position the brake pads afterwards, but it will work for 1/2-3/4'' of clearance without a problem.
The heater hose manifold will hold up quite well if you support the weight of the carb with an extra mount of some kind. A large volume intake can help low end torque and throttle response so try different lengths of hose to tune it to your needs AFTER break-in.
Most importantly, Have fun!

Agreen · Jan 26, 2014

Re: DIY guy went HT

The driveway idling was done in 20 degree weather with a good wind constantly blowing. Otherwise I'd have ridden it. I did monitor the temp with my on contact pyrometer pretty closely to see if the temp was climbing, and it seemed to have stabilized out pretty well at 190. So I'm not worried that I baked it at all, but I do agree that riding it with a load is the best break in you can do. It was just too damn cold to ride it once I got it all together.

I do expect a little bit of blow back, but really not that much. I've worked on some 2 strokes before and known how soaked the filter can get, but this one was just saturated. And I mean that thing was spraying seemingly more fuel out than in. I seriously think the port timing is off. I'm not looking for a speed demon here, nor do I want to port it to gain performance over what stock should be. If I want to go fast I'll hop on the Yamaha or take my Rx-7 for a spin. It just seems like something is off. I think I'm going to try and re torque the head bolts, since there seems to be a fair amount of black goo coming from around the junction.

As far as spreading the frame goes, I forgot to post a pic of what's going on back there. The rear frame is curved for the brakes to be close to the rim. Spreading it out looks like it will interfere with the operation of the rear brake. I was considering extending the chain stays so the dropouts could be lower, but that would reposition the wheel too, and completely defeat the purpose of not spreading the frame (brake to rim clearance). I considered cutting that section out where it's rubbing and welding a curved section in for clearance. I know my welding and materials would be good, so I'm thinking that the structural rigidity would be just fine, if not stronger. Then again, I keep reading up about people saying to not mess with the frame of a bicycle unless you're a bicycle frame expert. Well, that I'm not, but I have welded on several other things that (I believe) take much more torque than a bike frame. Is there some sort of magical force on a bike frame that I'm not aware of, or is it more to deter amateur welders from mangling a frame and endangering someone's life?

Agreen · Jan 26, 2014

Re: DIY guy went HT

And to clarify, that's degrees Fahrenheit, not Celsius.

Thanks for the advice, by the way. I appreciate you guys' concern for me blowing things up. I'm no bicycle mechanic by any means, nor am I much of a 2 stroke expert. I am, however, an auto technician turned nuclear operator, so I feel like I know a thing or two, but I'll still humbly accept any and all good advice.

-Terrence

48ccbiker · Jan 26, 2014

Re: DIY guy went HT

Most 2 strokes have reed valves which prevent the carb "blowback". This engine is just piston port intake which is why it does that. If you do any porting on the intake it will do it even more. The NT carb does not have a true idle circuit which is another reason you see so much gas spray. Buy a good carburetor.

Agreen · Jan 26, 2014

Re: DIY guy went HT

I've been reading Gordon Jennings' tuners handbook. While it's geared towards performance, it also could be used for engine efficiency as well when properly tuned. Seems like a well tuned expansion chamber could solve some of the blowback, since it creates a vacuum using resonance during the exhaust sequence, then a slight pressure once the intake port is covered, forcing any intake charge over shoot back in the cylinder for a more complete combustion. Obviously it will increase the combustion pressure more, but if I design one for mid rpm operations then it should also in theory eliminate that blowback and assist with me having to give this poor thing **** to get over 20 mph.

That'll be down the line though, so well after I get it all broken in properly. I'm looking at this frame here and seeing that I can indeed spread it at the point I couldn't before. I was afraid the brake pads wouldn't make proper contact after spreading it, but now I see that they are indeed adjustable, so I'm going to give that a shot. Beats the **** out of cutting and welding it all to pieces.

I'm assuming you recommend a mikuni carb set up similar to what you have on your blog? Obviously with a larger jet for the larger displacement engine. I'm not opposed to making a new manifold, and any flange out there is well within my bounds to fabricate.

Theon · Jan 26, 2014

Re: DIY guy went HT

An old pair of handle bars, is good 22mm tube with nice bends for making manifolds for larger carbs, I'll take a picture, this manifold gave exceptional Low down on my motor using a speed carb. I doubt that your problem has anything to do with your carb though.
More likely Crappy rings, Bad port timing, Badly seated head, Restrictive transfers and Restrictive exhaust. And I'm not talking about building a race motor, just something that works like it should.
Some of the expansion chambers on the market don't look all that good to me, designing/ making your own is a very good option, however I have found a good (some are better) standard pipe with the inner tube cut back and match ported! gives good performance up to moderate revs.
Mate if there is black oozing from around the head,I'd take it off.
It sounds to me that you have sound mechanical knowledge for this task.
I always give a head a lap with a piece of wet and dry on glass.
And have seen a few bruises on mating surfaces from parts being miss handled before assembly.
Once back together retention head 3 times with heat cycle in-between.

Agreen · Jan 26, 2014

Re: DIY guy went HT

I torqued the head nuts down to specification. I read 120 to 140 in-lbs was good, so I hit it with a torque wrench and found them each to be about .5 turns loose each. Wow.

I think the carb may actually be an issue, since I started it for the first time today after torquing the nuts and it 4 stroked on me for a bit until the extra fuel burned off. I gave it **** and after a little bit it came back. I went back to the garage and noticed there was a pool of fuel on the ground from before I pulled it out. So I thought it had a bad seal at the float needle. So I pulled the carb apart and tested the shutoff with some lung-powered air pressure from a new bit of fuel line to the inlet and found that it was fine, so I adjusted the float down a bit and went for another ride. Better, but not great. I'll probably tinker with the carby a bit more to see what I can do for it, but this is by far the worst carb I've ever dealt with.

I'll be pulling the head if the black goo returns. If the loose head nuts damaged the head gasket then I'll pull the head and true it up before replacing the gasket. I'll just have to see if this is going to work first. Once it cools I'll hit it with the torque wrench again and repeat. If they keep loosening on me, I'll get some better studs and nuts too. I couldn't imagine they're too terribly high quality in the first place. They are, at least, the 8mm studs, so that's good.

Theon · Jan 26, 2014

Re: DIY guy went HT

I have a couple of brand new carbs here , the standard, and the 'speed',
My camera battery if flat, but from gasket to float arms (while the carb is upside down) is about 3mm if this helps.

slayer60973 · Jan 27, 2014

Re: DIY guy went HT

This may be a bit off topic but I recall reading that you have an rx7? If so id love to see that beautiful rotary powered machine. As for your motor, accelerate to about 20mph then brake, not hard but quick enough to get down to 10 or so mph. With the clutch not pulled in .This creates a vacuum and helps create better ring seal. Just be smooth with it though. And it also sucks out any small metal bits in the engine. Got this advice from a professional motorcycle mechanic. Did this with my engine and after 300 something miles I have little to no blow by on my piston. As for that rx7. You are a lucky guy. I've wanted one since I was 7

Agreen · Jan 27, 2014

Re: DIY guy went HT

OK, so new update!

I got to thinking while I was at work this morning (mid-shift) about the head's lack of torque and what all else that possibly affected. If it was allowing extra blow by, then it probably needed to run rich to stay running. So I got home a few minutes ago and took the needle out and adjusted it down (e-clip up) to the last notch. I went for a ride and it didn't want to start via normal pedaling and dropping the clutch. That's because before I never had to put the choke on. So I set the choke and dropped the clutch and it sprang to life without 4 stroking this time. After a little bit I eased off the choke and gave it a roll on the throttle. Much... much better throttle response, great power, and much smoother now. Seemingly this is where it was supposed to be all along. Keep in mind the 1/2 turn on each but was an average. One of them went a full turn before reading 130 in/lbs. That was one loose head.

So now I'm satisfied with it. Once I get it broken in I'll start tinkering with it some more to see if I can squeeze a little more out of it, but I definitely don't want to push it past its safe point.

And after sitting all night in the garage there was no sign of leaking gas, so now I know the float issue is resolved.

So there we have it. It was a culmination of a few problems all together that made it suck the way it did. The manufacturer obviously doesn't have high standards for quality control. Which is fine by me. Keeps the cost down, and I sure do love tinkering with problems like this. Makes things interesting.

I've definitely been using the engine braking technique a lot too. I have a somewhat hilly area around my neighborhood, and I always try engine braking it down hill to keep the speed down and engine turning for a good break in.

As for pics of the rx7, you can kind of see it in the background of a couple of my pics. It's an 88 convertible converted to a turbo drive train with some decent power adding modifications. Like the T04B hybrid turbo that I built, a standalone ecu that I also built, and a v-mounted intercooler/radiator that I fabbed up. It's not the most gorgeous thing in the world, but I sure love it. It's pushing about 350whp at 15 psi, 93 octane. Gets on average 13 mpg. God I love rotaries

Pics:

]

Theon · Jan 27, 2014

Re: DIY guy went HT

I had one once, just a standard old 12a with a rev limiter and a loud exhaust,
But a lot of fun and a lot of fuel!

slayer60973 · Jan 27, 2014

Re: DIY guy went HT

Agreen said:
OK, so new update!

I got to thinking while I was at work this morning (mid-shift) about the head's lack of torque and what all else that possibly affected. If it was allowing extra blow by, then it probably needed to run rich to stay running. So I got home a few minutes ago and took the needle out and adjusted it down (e-clip up) to the last notch. I went for a ride and it didn't want to start via normal pedaling and dropping the clutch. That's because before I never had to put the choke on. So I set the choke and dropped the clutch and it sprang to life without 4 stroking this time. After a little bit I eased off the choke and gave it a roll on the throttle. Much... much better throttle response, great power, and much smoother now. Seemingly this is where it was supposed to be all along. Keep in mind the 1/2 turn on each but was an average. One of them went a full turn before reading 130 in/lbs. That was one loose head.

So now I'm satisfied with it. Once I get it broken in I'll start tinkering with it some more to see if I can squeeze a little more out of it, but I definitely don't want to push it past its safe point.

And after sitting all night in the garage there was no sign of leaking gas, so now I know the float issue is resolved.

So there we have it. It was a culmination of a few problems all together that made it suck the way it did. The manufacturer obviously doesn't have high standards for quality control. Which is fine by me. Keeps the cost down, and I sure do love tinkering with problems like this. Makes things interesting.

I've definitely been using the engine braking technique a lot too. I have a somewhat hilly area around my neighborhood, and I always try engine braking it down hill to keep the speed down and engine turning for a good break in.

As for pics of the rx7, you can kind of see it in the background of a couple of my pics. It's an 88 convertible converted to a turbo drive train with some decent power adding modifications. Like the T04B hybrid turbo that I built, a standalone ecu that I also built, and a v-mounted intercooler/radiator that I fabbed up. It's not the most gorgeous thing in the world, but I sure love it. It's pushing about 350whp at 15 psi, 93 octane. Gets on average 13 mpg. God I love rotaries

Pics:

]

Very nice car man. If intake blow back starts to bug you there's a very nice intake manifold made by cr machine man. I think it's called the power plenum? Or something like that. It's supposed to help with limiting blow back. It's a bit pricey though. But cheaper than converting to a full on reed valve setup. I wanna getone when I save up enough money's.

http://www.shop.crmachine.com/Intake-Manifold-Plenum-Boost-Chamber-IPBC.htm

Agreen · Jan 28, 2014

Re: DIY guy went HT

Upon a partial engine teardown inspection I'm finding some interesting points. First off, I'll be trimming the piston skirt a tad on the intake side and doing some fine file work on the pports. Quite a bit of casting flaws and the piston skirt is about .250" too low, so not completely allowing full flow to the crankcase. The gskets are cut so badly that the intake and exhaust ports are about 1\2 covered by gasket material. Most notably is the fact that the cylinder walls look like total dog poo. For a brand new engine with about 10 miles on it (maybe 1\2 mile at wot) the cylinder walls are already showing some minor scoring, probably from the poor deburring job that was most likely not done. The head and jug flanges have pits from what looks like a preschooler trying to shove the square peg in the square hole, but lacked the proper motor skills to get it anywhere near aligned.

I have a small brake caliper hone that I'm hoping to take care of the light scoring, and I'll probably have to shave the mating surfaces of the head and jug to get rid of the dings. I'll also be getting a new head gasket, since the one on there now looks like it got sandwiched improperly during installation. One side is pinched , other side completely flat.

Once again, I'm not looking for massive power. I'm going off experience from the last motorized bicycle I made, and how smooth it was and the comparison of power bands. That was a 42cc poulan chainsaw engine before, so this one should outperform it without a sweat, right?

Theon · Jan 29, 2014

Re: DIY guy went HT

Hate to say I told you so, but all these motors need stripping and rebuilding properly from the start.
Do not trim the piston all the way to the port opening!
Do not worry about a few scratches in the bore,
Do not put a hone through it!
The cylinder wall is a very thin chrome plate and very easy to wear through with a hone.
Do the rings look as though they are sealing, is there any sign of blow by on the piston below the rings?
Before trimming the piston get a protractor!
Do not trim the piston past 60 deg BBDC (120 deg total inlet duration).
Did you get the clutch removal tool?
If so remove main drive gear and check the seal behind this and the Mag were put in straight. If you have a Dremel or similar then consider doing a bit of work on the transfer ports, not changing there heights, but just taking out the restrictions.
I would widen the exhaust opening, but not take to much out of the roof, again use a timing wheel/ protractor.
Start by finding TDC accurately, I usually do this by bolting the head back down, with piston but no rings installed and using a piece of solder to do a squish test. you may need thick solder. your squish should be 1mm but that may give higher than desirable compression ratio with a standard angle fire head.
Which head do you have?
After finding TDC and tightening the nut holding the protractor to the Mag so that it lines up with a screw head or something, check all port timings.
You want the transfers opening at around 120 ATDC, this figure is up to the individual, but adjust base gasket thickness to suit.
Then mark and trim inlet skirt.
Then lift the exhaust if necessary to suit and give the desired blow down time.
I hope this gives some inspiration.

Agreen · Jan 29, 2014

Re: DIY guy went HT

Before I proceed, I'll post some pics of the inside of the cylinder. With a flashlight, I just started noticing some pits. Looks like nothing I've ever seen before. I've run into chipped chrome before several times (rotaries have a chrome coating on their rotor housings) but this looks different.

As for signs of blow by, there are none... yet.
Standard slant fire head.
Yes, I have a clutch removal tool

Let me go bundle up real quick to take some pics.

DIY guy went HT Motorized Bicycle

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