BGF Hongdu/Solex

[Mike B]

I dunno. The motor looks good. Cranks over by hand, not a lot of compression, but the compression release works. The tilt handle went through the box, so maybe my hook is somewhere between here and Canada. The flywheel cover hits the flywheel lightly in 2 spotsthe middle cover says 4800 on it and doesn't fit well. The top cover has "Start" and start in another language with an arrow for the choke lever which is actually an enricher I guess.

Another thing I noticed, I guess these things are wide open throttle default and the "gas" lever slows them down?

I dunno, this is my first "Solex". Bought it because I always thought they were cool.

There was no decal on the tank and the hose they put on for the tank breather is no good. I'll post some pics when I get home today. Was going to last night, but I was too busy going over it and finding out all this stuff.

I still think they are cool. Funky looking, but cool and nostalgic. I do have a proper air filter though with the little backing ring on it. The spark plug also looks decades old.

Maybe I hit the jackpot eh?

 

[wayne z]

Jackpot for sure if it's an original, they run a lot better than the clones. Which vendor did you get your kit from?

 

[Mike B]

The guy in Canada.

Solex 49cc Motorized Bicycle/ Kit Engine Bike Motor | eBay

All new construction -

 

[Mike B]

Pics

Here's the rusty gas tank. Rust on the inside, rust on the outside. See that rust I exposed under the blister? See how half the back of the tank is blistered?

The muffler is brand new

As I said, the motor looks straight.

A 4114 spark plug

The castings all look very nice, much better than HT stuff.

And here's the grindstone friction drive

I dunno, what do you experts think?

 

[cannonball2]

If its an original Solex it will have a serial# near the front of the engine case. The Hongdu doesnt. Also the Hongdu fuel cap is a female thread, I believe the Solex is a male. Sounds like a Hongdu with the earlier style roller. Seems they are all slightly different. The original as well as the Hd runs @ WOT and is returned to idle when the brake is pulled. I have set one up both ways and the WOT set up makes the best sense as that is where the engine lives most of its life.

 

[cannonball2]

Thats a Hongdu. At least you got a good cylinder casting, the roller is not like the Hds I have nor the original Solex I have. Pull the nut of the crank cover an see if there are points, my guess there is not.

 

[Mike B]

Nah, no serial numbers anywhere.

There is a HD on the cast iron cylinder though, yeah, HongDu it is.

They must have got that rusty tank out of a scrap bin then. I did notice that one of the tank screws was not fully fastened.

I don't care, I knew it was China stuff when I bought it. The POS gas tank was a dissapointment though.

Maybe that is original Solex -

 

[cannonball2]

Some things to check. The compression releases have been too tight on both of mine, you may have to loosen the nut to allow the proper travel. If you switch to a long reach plug it raises the compression and the running is improved. If the plug in yours was like mine, it doesnt even come to the bottom of the threads in the head. The area in the head is so small that simple differences in plug dimension affect it. My first engine had one head gasket, the second had two for what reason I dont know. Depending on how far you want to go into the engine checking it, I pulled the head, lapped the compression release, and checked eveything out, just to see. All of these are different it seems, depending on who put them together and with what. Maybe these are rejects, or engines built from marginal/bad parts. My first engine was very good with only dents in the fuel tank, the second engine was nicer in most ways but had a marginal cylinder casting. I cant imagine this is a first run product.

 

[cannonball2]

Forgot to mention the sparkplugs. I am running a Bosch W8BC, a Champion L92YC works also. These are medium heat range.

 

[wayne z]

That gas tank is about normal for these kits. Both mine were very scaly and rusty indide. They are ok after cleaning with gravel,being careful about the in tank filter and using rust neutralizer.

You can cut the tailpipe to 3/4" long and drill a 6mm hole in the bottom of the muffler to help performance some. Run a drill in the tailpipe to be sure it isnt restricted with welding slag.
I used a piece of small dia coil spring about 1" long on my comp release cable to give the lever some feel and travel.
Also drilled out the 2 air cleaner inlet holes to 6mm.

First tank of gas was 32-1 mix. I used 40-1 after that.

Don't expect it to run real good until you get a few miles run in time on it.

If you haven't already, you should go back and read all the posts in this thread.Wealth of info on this kit.

 

[cannonball2]

Finally have what is supposed to be a good used original Solex engine comiing for my Velosolex project. I also have a new original piston/cylinder/rod assembly. The idea is to install the new parts on the Solex engine, then if the parts removed are in good condition, install them in the #2 Hongdu. Should be interesting to see if this makes a big improvement in power. My gut feeling says yes.

 

[jones0055]

Hi,

Firstly, thanks to all of you on this post, without it and the pictures, I would have been messing around for a lot longer. I just installed my first solex motor on an old bike. It's going quite rough but hopefully that will improve.

I have a couple of questions that I'd really appreciate if you have the time to answer:

1. which way is the accererator cable attached to the carb - anyone got a picture? I can't work out if mine's the wrong was round or if there's dirt blocking the fuel when I pull the lever. It seems to choke off fuel rather than provide more to the engine.

2. My kit didn't come with any of the mounting brackets that are in Cannonball2's pictures (the two flat plates between the engine mounts and the forks and the long thin exhaust stay). Were these part of the kit or did you make them yourself? If you made them, do you have a template you could upload or if not, anyone know where i could get them from? This is the main reason it took me a long time getting the motor onto the forks - all I could find were decking brackets that I had to hacksaw into shape (not really a pretty sight!).

3. I have the rusty tank problem - has anyone modified the fuel pipes to put a filter in?

4. Finally, anyone know what the spark plug gap is supposed to be and what the best plug is - any recommendations??

Cheers!

 

[wayne z]

Hi,

Firstly, thanks to all of you on this post, without it and the pictures, I would have been messing around for a lot longer. I just installed my first solex motor on an old bike. It's going quite rough but hopefully that will improve.

I have a couple of questions that I'd really appreciate if you have the time to answer:

1. which way is the accererator cable attached to the carb - anyone got a picture? I can't work out if mine's the wrong was round or if there's dirt blocking the fuel when I pull the lever. It seems to choke off fuel rather than provide more to the engine.

2. My kit didn't come with any of the mounting brackets that are in Cannonball2's pictures (the two flat plates between the engine mounts and the forks and the long thin exhaust stay). Were these part of the kit or did you make them yourself? If you made them, do you have a template you could upload or if not, anyone know where i could get them from? This is the main reason it took me a long time getting the motor onto the forks - all I could find were decking brackets that I had to hacksaw into shape (not really a pretty sight!).

3. I have the rusty tank problem - has anyone modified the fuel pipes to put a filter in?

4. Finally, anyone know what the spark plug gap is supposed to be and what the best plug is - any recommendations??

Cheers!

1 the throttle on these is normaly set up to run wide open when lever is released, and idle when the lever is squeezed. once you drive it you'll understand why it works good this way.
2 you could get some 1/8x1" strap steel and use vise with wood and or metal forms and presss to shape/cut drill, hammer ect. to make yer own. Someone here welded their plates directly to the forks.
The flat plates woule be simple to fab from some 1/8"x3" flat steel or aluminum stock

3 Read older posts of this threas to see how others dealt with rusty tank. It is salvageable.

4 again All this is in older posts. If you don't read them, yer missing a wealth of info.
Yer gonna like this little engine.

Wayne Z

 

[cannonball2]

Well I finally got enough parts together to restore the engine for my Velosolex. This left me with very good used parts from the restoration motor. So into the Hongdu on my Macargi 24" they went. I installed a cylinder head, cylinder, piston/rings/rod assembly and intake exhaust manifold, kept the Hongdu carb. This all bolts readily to the Hongdu lower end. There are major differences in the design of the parts. The piston port timing is different(I assume cylinder also). The cylinder head deck height is much lower on the Solex, rasing comperssion(Waynez already noted this). The Solex uses thinner base and head gaskets. My Hongdu had 2 head gaskets the Solex uses one. Any way this all adds up to the best this engine has ever run. Runs great from start, no 4 stroking until it warms up. Winds up to a higher rpm, top speed has gone up from an average around 19 to 21. And it makes slightly more power on hills. The biggest noticable differences are the higher rpm, and the extremely clean and crisp running. If the Hongdu crank bearings hang in there, this little engine seems like it could run forever.

 

[wayne z]

I decided to shave the head on engine #2 today. It already ran sorta good, top speed of 15 mph.

The deck height on this one was slso .100" ,The specs say it should be .060 and the other motor ran almost normal after shaving it to .060.

I shaved this one to .045 deck height, leaving about .020 squish left with head gasket in place.

Wow!! top speed increased to 21 mph! You can actualy feel acceleration now,even on slight hills.
That steep hill down the street, that it couldn't make before, it now pulls at 10 mph.
I actully have to throttle it down now in the driveway ect.

It now runs fastest with the enrichener on. This tells me that I need to drill the jet slightly larger to match the improved engine performance.

So, if you want to increase your Hongdu performance dramaticly, shave the head to .045 deck height. and fiddle with the jet some.

The fun factor also goes way up when they run this good.



Wayne

 

[Mike B]

That's good to know. My project will be awhile, have a few more ahead of it on the list.

I am thinking about putting it on one of these.

 

[wayne z]

CHECK yer FLYWHEELS!

Mine wasn't tight, and after improving the performance with head shaved, the power pulses are stronger.

A loud chattering started in the flywheel, and the motor quit.

I pulled the flywheel, and the cast-in key was sheared off.
There was a slight nub left at the outside edge of the hole.
I used this nub to align the flywheel to the keyway,and tapped the flywheel onto the taper with a hammer and large socket on the flywheel face .
Then I put on the nut and tightened it lightly with a battery impact driver.

After removing the nut, I centerpunched a spot at the edge of the flywheel hole, centered on the keyway.
Carefully drilled a 7/64" hole down the keyway,in the flywheel hole edge,about 3/4" deep.
The bit miked at .110. I found a finish nail that miked .112, cut a piece about 5/8" long and drove it in there with a small punch.
Then re assembled all, and ir runs great again.

Wayne Z

 

[wayne z]

That's good to know. My project will be awhile, have a few more ahead of it on the list.

I am thinking about putting it on one of these.

That's a great project for on of these engines.

They push start very easily. I can sit on my bike and take 3 striding steps and it starts right up.

You can use a rear axle mount kickstand on the front axle like I did, to keep it upright and stable an when parked.

 

[cannonball2]

Hey Wayne, if you want to fool around with timing, lap the flywheel to the crank with valve grind compound for a lock on fit, then advance it 1/2 the key way to start, I bet that will really wale it up!

 

[Mike B]

How did you shave the head?