All new parts but still wont crank well past compression

[alex71]

Hi all, i am new here but been reading posts about similar issues without luck.... so here is my first post.


So the engine in question is a Zongshen 167FMM/CG 250 watercooled. It sits in a Bashan 250 quad and will be a great help on my farm, i hope



The problem for me is most people with similar symptoms all over the net i have read about have either not replied with their fix, cause it was probably a bad wire or something or found the cure which unluckily for me is not what my issue is.


I owned a large garage in the UK for over 30 years and was also a diagnostic specialist so fixing this bike should be easy for me but with the funny problems/quirks these Chinese bikes can come up with this one has left me sort of scratching my head.... but an engine is an engine, suck,squish,bang, blow



Got given this quad years ago, it had a very bad starter in it which i thought was the problem, it would start occasionally and then run fine unitl you needed to restart it.
Im lucky here in Portugal as i have thousands of miles of dirt fire roads around my farm and the bike went well for a few half day runs, if it stalled it would be hell to restart and with no kickstart often meant the wife coming out to pick me up.
The quad was then left sitting for a few years,,, until now.


So we get and fit all new= starter motor, KF Japan PZ30 carb and a Yuasa 12v 9AH 115CCA battery...and a new CDI just to eliminate the CDI that came with the bike.



I didnt doubt any of these parts as the bike did run if it would start, only thought at this time was pickup coil or CDI.
older starter was burned out, needed a new battery and replaced the carb as had seen better days.

years back i previously suspected poor "Asian" wiring so i cut out all the lights etc and re-wired most of it also made new starter motor feed cables as i know the standard ones are way to thin. all checked and O.K


So we go to start it and it is the same as it always was, starts to crank well but slows on compression stroke then passes and speeds up for one more revolution then back to slow, no real kickback that you can feel but that is what is happening and as it only has electric start i cant try and kick it over.


Removing the spark plug lead while starting removes this issue and she will crank well for ages, click spark lead back on and instant problem again.

So it is advanced ignition timing causing the problem!


A pretty easy one to diagnose........ yeah right!

I put a timing light on it but with spark plug removed and cranking it over as it wont start at this point.
i do not see the F but the two | | marks in the window with the light, so it is firing on the advanced marks..... am i right here?
(A cg125 manual states using the light you should see F in the window)



I know it is firing early but by how much and why i dont know yet

I can not find any timing information on this exact engine but will check and report the angles, position of the timing hump, when i next remove the side case. if i can get it running again i will check with my timing light again.
Anyone got any help with this info would be very welcome.



So at this point i suspect the pick up coil in the stator.......... we buy a complete new wiring harness kit that comes with everything, CDI, stator and pickup coil, regulator switches etc.
Fitted all this and my new upgraded cables for the starter wiring.


We also bought a new sprag / starter clutch as I know they can go bad with similar chinese quirky bad start and after the days/weeks of cranking its had i thought it cant hurt.


Side case off again, keyway is fine, flywheel looks undamaged.



The original starter gear where the clutch engages looked a little rough but the new clutch came with a new gear so all good there.



All these new parts fitted and still the same on cranking so not the pickup coil or starter clutch.
The starter idler gear and large starter gear also look ok and have all their washers.



check valves again just to be sure it isnt the valves, all ok at 0.08mm. got good compression!





Side case off again.... This time i remove the crankshaft oil seal and take a look at the timing gears............... the crank timing gear has either slipped or been fitted badly.... see attached photo.

The "0" is off from the woodruff key by exactly one tooth clockwise on the crankshaft by checking with straight edges etc.
As you can see the upper valve gear "0" is lined up correctly with the "0" crank gear so that means it had retarded valve timing too


(I only know this engine with starting issues, i dont really know the history of it but the guy who gave it to us said the guy he got it from said it had a fairly new engine.... who knows?! we all know how these little things get abused)


So off comes the head and cylinder to get at the valve timing gear.

I didnt take any pics but it has some hours on it but still has honing marks in the bore, no scratches and no signs of previous rust!


Head and piston were coked up so all cleaned and looked pretty fresh so maybe it was a pretty new engine, got this issue and hence it sat sitting around before we even got it, and then we left it sitting



Push rods, valve cam and gear and everything else all look brand new, no signs of any wear and measure good.



I then move the upper valve timing gear to the left of the offset crankshaft "0" by one tooth.
The upper valve timing gear "0" now lines up with the woodruff key as i believe it should and looks very inline now.

So valve timing should be back to very close to normal. I dont have the timing gear puller and currently looking for one online.


So i have advanced ignition timing, at least on starting and with my timing light it also confirms it,only at cranking speeds/plug out.
The flywheel woodruff key is OK, new pickup coil all confirmed as working as it had run, it is just when starting it has problems.


All i could think to do was to move the pick up coil, a bit of drilling and filling the pickup coil securing tabs i have managed to move it counter clockwise until it almost hits the inside edge of my side casing, i cant see it giving me much more that 3/5 degrees of retarded timing but at least it is in the right direction.



Can i pull the crank timing gear off and re-fit it correctly inline on these engines??


To me in a vehicle engine we would just fit a new one,,, if it slipped once it could slip again.... and the same in this case but i know this isnt a car and you can get away with reusing some of these simple engine parts.

But again with all the parts i can find online i can not find a crank timing gear anywhere in europe.still searching.

I can buy a new crank with a timing gear already pressed on for 70Euros.


But it means engine out, split it etc and with a 35 acre farm and 50 milking goats time is hard to find time, seems a lot of work just to change a gear i can replace with only the side case/ flywheel removed. Plus the engine is telling me it isnt thrashed,,,,, yet ,,,, so why change the crank, feels smooth when turned by hand.


Put it all back together,
Tried the original and the 2 brand new CDI's i have all with same result, but it sounded like it had slightly less problems passing compression, did that little retarding do something?

i think that is down to the valves now being in time and it eventually fired with the help of opening the throttle a little. i have to get the opening and release of the throttle just right and she fires, it aint right but allows me to see and hear it running.



I took it for a ride and she goes very well, exhaust also now feels a little cooler, again the valves are now (more) in time.

I know valve timing can also cause this and other issues but removing the plug wire and getting a good crank disputes this??


(When it ran when we fist got it, it ran just as well i think from memory.)

On the ride I stalled it, it started the same, sluggish on compression but she started.
I rode it pretty hard for several hours up steep hills, i live in a mountain range, these are steep hills! dirt tracks etc, didnt miss a beat, no backfiring or pinging, a sign of over advanced timing, lots of power, would idle for 10 minutes without any faltering at all, again no knocking or shakes while idling or under load, it sounds sweet when running,,, promising little engine but whats wrong with it



It went like that for last couple of days managing to just start itself with a slight throttle twist but you will only have limited tries at this before it draws the battery down enough that it the really struggles as the starter really pulls when fighting the kick back and i keep the starter going and normally will eventually fire.
I have battery testers here and battery is good, just shows how much the starter is working, with spark plug lead removed she will crank for hours.



Not knowing these engines very well all i can think of now is, what can effect timing...



The Crankshaft has some sort of twist even though everything looks ok?

(when cylinder was off the crank/con rod checked out good no excess play in any of it)


Could it have had a high comp piston fitted, pretty unlikely but i will take the head off again and take a pic of piston top, if i remember right it was just flat topped with valve recesses.



The slipped crankshaft timing gear, what i have done by moving the upper gear, is it 100% accurate enough?, it looks inline with the key after i moved it and these are only pressed on, no key, by lining up the woodruff key with the "0" by eye anyway..... but this is an ignition problem i dont think a valve problem but without any data i cant tell for sure (still like to swap out the gear as it could move again) but the kick back is being caused by ignition way BTDC as proved by removing spark plug lead.



So can anyone tell me what degree BTDC the pick up hump on the flywheel is meant to be on these CG250 engines.... i found a cg125 timing data online at 15degrees BTDC but i dont know if that is standard on all flywheels?

Can they go bad ?? causing the pick up to be triggered/fire early or other problem with timing.


CDI#s.
All give the same results and after looking to buy them online i assume these are standard, one fits all type deal,,"Motorcycle 6 Pins AC Ignition CDI Box for CG125 CG150 CG200 CG250 Scooter ATV Quad",, could i have the wrong one some how?

I checked some websites selling Bashan BS200/250 quads, same CG engines and all CDI's they have look the same as each other and the same as mine, so i dont think it is the wrong CDI but it would make some sense as heard some have over advanced timing.... i really dont know enough about these CDI's and the curves set in them.
All parts and wiring check as good.



To me everything is lining up, except for my pickup coil move i did but that was to retard timing and can only help it start in its present state and can be put back to original easily., so if i go messing around more with me manually retarding further, which doesnt look possible with the pickup coil anyway, any further retarding would effect the whole timing curve, when from how the engine sounds and pulls i think it is only on start the advance is an issue. Id rather find and fix the problem rather than mask it unless anyone has some ideas. 24volt starter



To me if nothing mechanical is twisted or out of spec and that can really only be the relationship between the piston crown and the woodruff key on the crank, and i am pretty certain the crank isnt twisted... so what is causing this to fire so advanced on start.
Piston sits at TDC and T mark line up, also checked with case off, woodruff key also lines up with valve timing gear 0 mark, as i have set it.
i know it will fire on F not T so assuming my flywheel is correct if T lines up with TDC everything is well with piston and woodruff key then it should fire at the F by whatever the degree is Btdc that i dont know, so that would leave the connection between the woodruff key and the (pickuo coil) hump position on the flywheel to be at fault, Very unlikely...



So do i have the right flywheel, is it bad some how?, as i said above i think i am right in saying the CDI is programmed one for all type of thing and it would be the flywheel hump that triggers the pickup coil that would be set at different degree angles on flywheels for different engines? 50cc 150cc 250cc



Sorry for the long post but i havent ever seen this problem in months of internet searching and wonder if it could also help others if i find the problem.


This thing has me stumped now and dont want to keep chucking money at it, so here i am hoping you guys might have some ideas



Cheers

Alex