bicycle engine tear down

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

Re: total tear down

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.

Re: total tear down

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.

Re: total tear down

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.

Re: total tear down

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

Re: total tear down

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.

Re: total tear down

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.

Re: total tear down

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

Re: total tear down

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.

Re: total tear down

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.

Re: total tear down

it bolts together with 1/4-20 bolts. rough looking


this is how it would be used to ream out the bushing if I had pressed in a new bushing lacking a ream you might be able to hone it to size with a brake hone. If you get a bushing from a dealer after it is pressed in it might not need to be reamed.

Re: total tear down

this is the shaft that the cluth rides on and the front drive sprocket all layed out in the way it goes together I'm pointing out the clutch spring this is what puts pressure on the plates and not the little spring out between the plates. under the clutch spring in the picture is the shaft that goes inside of the main cross shaft. it is the shaft that the flower nut attaches to and pushes the pressre plate off the clutch pads pretty cool how it works. I reassembled this and greased the inner shaft and the bearing.

Re: total tear down

using typing paper I push the screws through it and screw them into the block to hold the paper then rub with dirty fingers to transfer an image of the gasket area on to the paper. I then remove the paper and cover it with scotch tape to build up the paper and so it won't tear then cut out the insideof the gasket pattern until it fits the part. I left the out side of the gasket pattern lots of room to make it stronger. I can trim the gasket after it is in place and all tighten up.


you can see how the pattern turned out. the hole for the shaft is left small and is cut to size after all the bolts are in the case and tight. that is when I trim the outside part of the gasket as well using an exacto knife the gasket is fugly but this is how to make it easy and not tear.


a very small amount of gasket glue on the outer couple of edges to help hold it while putting the screws in place I don't use alot and only in the places you can see.This side has a raised lip and its the side i pressed the flywheel into fisrt then install the gasket and the other side pulling it down with the case screws turning each a little at a time


closing up the crankcase take your time and it will all go together. Put all screws in place to help hold the gasket in place then screw all screws a little at a time to close the case. Trim the excess gasket material on the outer parts of the case with an exacto knife to make it look nice and don't forget to trim the excess in the cylinder hole and the cross shaft hole. I found this to be the easiest way to get that thin gasket inplace with out tearing it. sort of cheating but it works. I took great care to make the gasket fit the rasied lip around the case as you can't trim it later. the patterm I make made helped to make it all fairly easy. the pattern took 4 tries before I was happy with it and could use it.

Re: total tear down

thought I'd show you how to make a simple bushing puller


how to make the puller into a bushing installer

my sorry quicky puller I used a big nut instead of tubing. I should have left the pictures big it hard to read the board I hope you get the idea I could redo this if you need me to sometime.

Re: total tear down

pushed the shaft back into the case from the clutch side the bearing will sit recessed in the case,the bearing will bottom out on a machined lip inside the case.


looking at the side where the sprocket will go after the bearing is pressed in place the bearing will also fit in the case recessed and will bottom out on a machined lip and you can't drive it in any farther


the bearing is being put on the sprocket side of the shaft

Re: total tear down

not really pressed I'm not beating the heck out of it either


this is the hole where the clutch cable mounts in. I grease the hole with my grease gun until grease comes out around the bearings then I dig out the grease in the hole and wipe off the excess grease on the bearings this will lube up the shaft and all the insides of the shaft parts. I do this on all the engines when I put them in the first time. I dig the grease out of the hole where I put it in so if it expands it has a place to go. it might be over kill as you saw what was hiding behind the clutch when I first took it off.


you can see the grease coming out around the metal seal area of the bearing stop when you see it.
****** UP DATE**************************************************************
If you can just pack the bearing with grease and lightly coat the moving parts of the clutch rod with grease. There really isn't a need to fill the through shaft area with grease.

Re: total tear down

Ok all of the shafts get their parts put back on the clutch the sprocket and the front gear along with the keys and lock washers a small amount of lock tight will help if you want. The front gear is a woodruff key (half moon looking thing) it can be a little hard to get in place so you will need to use pliers to press it into its seating area or a brass drift to tap it home all of the bolts are right hand threads so it easy to put back together. Tighten up the clutch and sprocket nuts then put on the front gear tighten the screw down with out the star locking washer to seat the gear then put on the star washer and if you have it use a hand impact wrench to tighten up the screw. notice the rag?! that is how I lock up the thing to take off or put on the gears.
well all of the rest of the engine assembly has been posted before except for installing the wrist pin and the wrist pin keeper. I use needle nose pliers to put the keeper back in place and when you get it in the keeper will spin freely in the groove put rags around the crankcase cause you don't want that wrist pin keeper flying into the crankcase if you loose the battle puting it back in the piston the first couple of tries. I forgot to take a picture of that. anyway that is about all for this time. I need to post on a front wheel bearing cleaning and repacking sometime.unless someone else wants to.

The screw/bolt that holds the small gear on the crank shaft size::: metric die that fits this thread is M8 1.0 threads are 12mm long head is aprox 16mm in dia.