bicycle engine tear down

[Norman]

OK I was going to replace the wrist pin bushing and do all kinds of things well turns out I thought the wrist pin bushing was bad so I took it apart and after looking at the bushing and talking to Duane at Dax this must be kind of normal on these engines. I had this apart before and the way the piston could wiggle around in ways I didn't think was proper in the china engine world is ok. but the minute I hear something funny its going to get a new bushing. I hope I'm close to home when that happens. I put a 36 tooth sprocket on so the cruise rpms is quite lower maybe it will last.
I'm posting the pictures and some information I did not take pictures of all the tear down as I have the same stuff on other posts. Some things were easy and fun some I should not have done and the gasket for the crankcase for me was ornery to get right. Well lets start with the show.
Norman

[Norman]

bicycle engine is in the stand. The sprockets nut has been removed along with the lock washer and the puller is used to take off the sprocket.

[Norman]

after removing the nut and lock washer pull the clutch off with the puller. Well greased isn't it the clutch didn't slip so the grease was not getting on the pads

magnet holding the key. can't see them but there is 2 shims on the shaft and what a nasty thing.

[Norman]

Here is where I got into trouble I took this apart don't to it as about 56 little ball bearing will go all over the place and hide on you what a pain it was to find them all at least I keep the floor clean so I found them and it was not fun to put back together. Lots of 4 letter words like darn and dang. What looks like dirt or grease is the sorry little bearings plotting against me on which way to run next


Big socket I have that fits to press all back together. Grease used to hold the ball bearings in place. If you just got to take it apart don't say I didn't warn you.

[Norman]

This is what is stamped on the seals on both sides of the bicycle engine in metrics . this is the ignition side

Gear box side

[Norman]

1. before you remove the piston mark it so you know which way is forwards if you put it in backwards it might hang a ring up on a port and destroy the thing. I later marked it with a scribed arrow to the front.

2. My wood piston support and pointing to the wrist pinkeeper

3. getting ahold of the keeper I remove it with sort of a twisting and gentle pull I remove only one keeper. I would replace it with a new one if I had one as you are not supposed to reuse them but being careful not to distort it you can get by notice the rag that is in case the keeper jumps into the crankcase.

4.There the little booger is sort of like pulling teeth.

[Norman]

Here is the wrist pin


Take a look here is the bushing in the rod see how its not centered. That is the reason I'm leaving it alone for now. That few thousands make the rod just a tiny bit longer and can change things. With the cylinder on and a 0.030 base gasket my piston top comes out of the cylinder and the head gasket keeps it from hitting the head. On Briggs flathead alcohol engines we decked the block so the piston would pop up out of the cylinder and the rules use to state no more than .005 pop up if I remember right. But that is on a 4 stroke.

[Norman]

the case screws are all out and 3 pictures of them. Only one has a lock washer on it and it goes under the clutch. The other two under the clutch don't have lock washers. I wonder if someone was lazy or out of lock washers or just goofed. I put them back the way they came out.


measuring tape so you can see the length of them just for reference

[Norman]

when driving out the shaft there are a couple of shims that were hiding in plain site on the shaft

got them in hand for better view

to get this out tap it lightly with a plastic hammer from the clutch side better read this all the way through cause what I first put on here to take the shaft out is not the best way. This is the clutch spring and the goodies that make it work. don't hit it hard or you will damage the smaller clutch rod in the middle. I have cave man ways with a hammer. the bearing on the sprocket side will come out with the shaft. Since this post I've found that it is better to drive the shaft out from the sprocket side less chance of dinging the clutch rod inside the main shaft. Do use some thing soft on the shaft so you don't damage the threads on the shaft pad it with wood or plastic. if you have it a press or an arbor press and take is easy these cases will break if you get just a little bit western with it.

[Norman]

all apart now to clean it up

I made a bushing reaming jig and I'll show you how its made

here is what it looks like with the top off it made out of flat strap and welded together not real pretty.