Problem: main bearings & valve timing (139QMB scooter).

[WmY]

Replaced the main bearings.

Note: timing chain sprocket on the crankshaft is pressed on outboard of main bearing. It must be removed before replacing main bearing. There are no marks that I noticed on the crank or sprocket indicating position.

After the main bearing was replaced, the timing sprocket was pressed back onto the crankshaft in an arbitrary position, since there were no position indications.

The timing marks on the camshaft chain sprocket do not line up precisely as they are supposed to. They are only close. There is no adjustment.

What to do?

Edit: in case it's not too clear, the alternator flywheel is pressed onto the crankshaft, and has a Woodruff key to position it precisely. There are marks on the outside of the flywheel to allow the chankshaft to be set to where the piston is at TDC. On the other end of the crankshaft is a sprocket for the timing chain, which has no obvious marks and certainly no key to position it on the crankshaft.

The camshaft sprocket looks to be fixed in position, with no adjustment possible. It has marks stamped into it to align with the cylinder head top face for timing, but no adjustment seems to be possible.

The timing chain sprocket on the crankshaft could be pressed on in any arbitrary position, but then the camshaft timing marks won't line up.

This seems a horrendous problem!

[WD Forte]

set crank according to rotor and case marks for tdc
set cam sprocket to case marks check both cam lobes midway (EDIT: BOTH VALVES CLOSED! not on overlap)
so not 180 degrees out.
offer up chain to unpressed crank sprocket so when fitted chain links coincide with sprocket teeth (allow for tensioner)
fit sprocket and mark it for reference
turn motor a few times and line it back up to TDC using rotor/case marks
Observe relative crank and cam positions and remove and adjust bottom sprocket as necessary

I'm guessing it's probably occurred to you that if you had marked it before you removed it.....................
____________________
bikers smell of wee

[WD Forte]

If you look here you'll see a crank at cmpo
(a mere 52 quid !)

https://www.chinesemotorcyclepartsonline.co.uk/partno_CRNK001


the pic has a zoom function and zooming in shows a sprocket tooth aimed at the center of the
crank pin (as near as)
Aim that at the centre of the cam shaft.

I reckon setting up with that as a reference will get you within a few degrees
as long as other conditions are met.
Half a tooth would be 10 degrees out, a smidge would be a piddling degree or two
____________________
bikers smell of wee

[WmY]

Thanks very much for that. I guess there is a tool somewhere to align the crankshaft sprocket when pressing it on. I'll ask Pedparts if they know, since they sell the bearing kit....

The 139QMB-E Kisbee's gudgeon pin is 10mm, so the "normal" crank with 13mm gudgeon pin won't fit, and the 139QMB-E one seems, unfortunately, to be £130 not £50-odd! Ow!


The engine's largely rebuilt now and I am wondering about something....

1) The alternator flywheel with the "T" mark is located by a woodruff key. It's fixed.

2) The cam sprocket position is similarly fixed (two set bolts, central hole).

3) The thing that links these is the chain. The crank sprocket is pressed on and (hopefully!) immovable.


So, if I position the crankshaft and the camshafts, and hold them, then re-introduce the cam sprocket, without bolts, at (say) about 90 degrees to normal positoin with the chain on and tensioned, I could mark the PCD of the existing bolts, and positions for new holes through which to bolt the cam to the camshaft boss, and it would be dead on. New marks could be made on the cam pulley for future use.


Would that be better than repositioning the crank sprocket?

[WmY]

[WmY]

[WmY]

Um. The importer says it does not matter how the crank sprocket is pressed on as long as it's fully home.

That does not seem to be correct, unless it also does not matter whether the timing's out 5 1/4 degrees either way.

I'm tending to re-drilling and re-marking the cam sprocket, unless there's a good reason not to.

Any ideas?

[cb1rocket]

Just mark the position relative to where the old one is and swap over.
____________________
Honda H100S2 Rebuild - https://www.bikechatforums.com/viewtopic.php?t=253852

[WmY]

Ooooooo he's just gone off on a test ride. Fingers crossed...

I might write up some of the procedure later, there's a lack of info out there...

[WmY]

Write-up of 139QMB-E engine rebuild (also applicable to 139QMB, 139QMB-E has different conrod, head). (I hope I've remembered all the stages.... this is just supposed to be a help/timesaver for those who have not done this before).


A replacement crank complete is simplest, although a crank rebuild (below) is considerably cheaper for the 139QMB-E.


Tools: wood blocks, 5-25 nm torque wrench (£20+ id you haven't got one), jaw-type bearing separator/puller (~£20), ideally impact wrench electric or air, universal locking tool for variator and clutch, flywheel puller (~£5), other general tools.

Materials: Crankshaft complete OR bearings (and seals), gasket set, silicone rubber gasket, thread lock, grease, engine oil, paraffiin/paintbrush/plastic bowl.


Prepare to remove the engine: remove seat/compartment, panels: belly pan, foot board side pieces; disconnect wiring & other gubbins; remove carburettor & tie up out of the way; remove air filter box complete; disconnect rear brake. Photos pre-dismantling are useful.


Put scooter on main stand then chock up scooter on steel frame under foot board using wood blocks (bits of 2 by 4 or whatever) until stable and stand is just clear of ground. Undo bottom bolt of shock absorber. Undo the two bolts that hold the engine to the frame, push them out while supporting engine, then engine on stand can be wheeled backwards out of frame.


Remove exhaust pipe.

Remove drive cover, starter pinion, variator (easy with impact wrench), belt.

Remove plastic cowlings.

Remove fan. Undo (easy with impact wrench)/pull off the flywheel. Remove

Dismantle top end. Don't let the con rod strike the edge of the crankcase mouth as you pull the barrel off. Pull out the free chain tensioner arm.

Remove the offside crankcase cover.

Pull off the plastic oil pump gear.

Note, a tap using a hammer and a soft drift is helpful for separating joints. Do not lever on mating (gasket) surfaces with anything!

Split the crankcases. Don't drop the crank! The bearings run in steel inserts integral with the crankcases and should be a tight fit removable by hand only.

If you're replacing the crankshaft complete, that's it, skip bearing removal.


Bearing removal: If you're removing the bearings:

Pull off the oil pump gear (woodruff key, don't lose it!).

Pull off the timing chain sprocket AFTER CAREFULLY NOTING OR MARKING ITS POSITION!!! It seems that a tooth should indeed point precisely at the centre of the crankpin. All is not lost if you do not mark the position though, see NOTE below.

Pull off both bearings. These are an interference fit and will be tight. If you bought that £20 puller you may need to file the jaws to make them more tapered at the edge of each jaw (easy since it's made of cheese) when you pull off the drive side bearing as it's very close to the crankwheel.

Clean out the inside of the oil director ring on the oil pump crankshaft cheek most carefully! Blow it out with compressed air. Metal fragments lurk here.

Replacement bearings used on this 139QMB-E engine were:

1 x SC03A39CS20-NTN (equivalent 6302-17P53-NTN)
1 x 6204-C3-SKF Note: C3 clearance is recommended by bearing supplier for this application. The bearing with the collapsed cage that came off this crankshaft was standard, not C3.

These and the gear+sprocket were pressed on. You can carefully use appropriate diameter/length tube, washers and the variator/flywheel nuts to push them on if you are careful. Don't press on or strike the outer bearing race.

That's it for bearing replacement.


Carefully clean components in paraffing and blow out/dry with your air line.


Put it all back together, lubricating the parts as you go. Online manuals have torque settings, but their language is not-very-good-English.

Use a small spot of silicone sealant on each side of the crankcase mouth where you cut the crankcase gasket when you replace the barrel, also on ends of the rubber half-moon that fits in the head where it mates with the rocker box cover.


Re-fit the engine. Use thread seal/lock on mounting bolts. Turn it over a few hundred times with the plug out to get some oil around the system.


Connect up all the wiring & gubbins, replace bits using thread lock where appropriate, and that's that.



NOTE: If you lost the positioning of the crankshaft's timing sprocket it could be 10 degrees or so out when you re-fit it! But you can re-time the thing.


Find a bolt with the same thread as a camshaft sprocket bolt. Use rough engineering (rotate in electric drill, wipe against abrasive) to make up two short pointed grub screws (see attached photo) with clean threads.

1) Loosely fit the camshaft timing sprocket & chain, and set the timing as close as possible to correct.

2) Remove the camshaft timing sprocket, being careful not to turn the camshaft. Slip the chain off to one side.

3) Replace the sprocket but not chain, bolts finger-tight. Turn camshaft to exact proper position and then jam it there using springy pencil-thick pieces of kindling or what have you.

4) Position the crankshaft at the "T" mark on the flywheel.

5) Remove the camshaft sprocket, again. During these various operations DO NOT move the camshaft! Stick masking tape to the clean back surface of the sprocket, cut out for the cam boss hole.

6) Screw the pointy grub screws you made blunt-end first into th crankshaft bolt holes. A drinking straw makes a good holder. Leave the screws pointing out just a fraction.

7) Check flywheel still at "T" mark, put the cam sprocket back on CAREFULLY but about 90 degrees out of correct timing, fit the chain & tension it with a finger, press the sprocket against the protuding points to mark it. Hold it and mark the face of the sprocket with a new timing line using the top of the cylinder head as a guide. You might need three hands for this marking, i.e. a helper. Neither the cam nor the crank should move at all during this!

8) Remove the cam sprocket. Mark the new timing line permanently. Centre-punch the screw tip marks on the reverse, and drill new holes.

9) Re-fit. Check timing correct.


Pic is pointed grubs for camshaft sprocket marking.