maximus75

I need some help. I just installed the big bore kit in my cy23 fulie. Before doing this the enige would start in 3-4 pulls, now I cant get it to start at all. I have spark, new fuel, seems like good compression (60psi) tested with a glow engine tester which didn't really fit that good. Everything went together exacty how it came apart. It seems like it's not getting fuel. The plug seems dry. The only issue that I had was the piston was very tight going into the bore. The old piston and bore went together much easier. I had to really oil up the new one and kind of wiggle it in. I thought maybe I damaged the ring but it should have less compression if thats the case. Any advice would be appreciated.

davido666

Did you by chance reverse your fuel lines.

maximus75

No, I thought the same thing so I double checked. I even richened up the mixture screws to compensate for the larger volume. BTW are the pistons in these engines directional like a glow engine or can they go in either way? It looked the same on both sides to me.

hellya

did you make sure the dot/mark on the piston head went to the exhaust port side??

davido666

Did the kit come with a new plug?
Even when you chock the engine the plug still doesn't get wet?
Did you recheck the intake gaskets and make sure none are damage.
You could take off the air cleaner and chock it by hand. Cover the intake with you hand and pul a couple of times and see if the plug gets wet.

davido666

This is froms Daves rc FAQ
How should I install a new big-bore kit on my Zenoah or Chung Yang RC-style engine?
Here are some basic instructions to help you install a new big-bore kit or replacement top end for your motor:
1) Remove all outer engine parts from your current engine - remove the airfilter, carburetor and intake manifold; remove the engine shroud and ignition coil, disconnect the muffler, etc. The cylinder should now be bare with nothing attached to it.
2) Remove the cylinder by removing the bolts holding it to the crankcase. Gently slide the cylinder up and off. Remove the old cylinder gasket.
3) Separate the piston from the crankshaft. Remove the c-clips which hold the piston on the piston pin and bearing. Slide the piston off, and remove the piston pin, washers, and pin bearing if your kit includes new ones.
4) Put the piston ring on your new piston. Slide it down over the top. Be careful not to bend the ring or it may break. Make sure the gap in the piston ring is aligned with the little nub in the piston ring groove on the piston.
5) Re-connect the piston to the crankshaft. Make sure the arrow or dot on the piston is toward the exhaust (not intake) side of the engine. Make sure you have the pin washers at both sides of the piston pin. Install the c-clips at both sides to ensure the piston is securely attached. Make sure these clips snap securely into their grooves.
6) Place the new cylinder gasket on the crankcase. Slide your new cylinder down over the piston and ring. You may need to compress the piston ring slightly to get the cylinder on. Again, make sure the gap in the ring is aligned with the little nub in the piston ring groove. Slide the cylinder down slowly and smoothly. Try not to wiggle or twist it too much to avoid scoring the cylinder.
7) Reconnect the cylinder to the crankcase. Tighten the bolts firmly.
8) Reinstall the carb, filter, muffler, shroud, coil, etc removed in step 1. When reinstalling the ignition coil, place a business card between the coil and the flywheel. Turn the flywheel so that the magnets pull the coil and flywheel together, pinching the card. Now, tighten the ignition coil bolts. This will ensure you have a proper gap between the coil and flywheel.
9) Once all parts are reinstalled, fire up your new engine and enjoy your new, more powerful machine! Be sure to heat-cycle the engine several times (run the engine for a few minutes at a low, varied throttle, turn it off and allow to cool, then repeat) in order to allow the new parts to properly seat themselves.

maximus75

No, I didn't even notice that second dimple. Could that cause a no start?
The plug barley gets wet when I choke it by hand and it did come with a new plug. I pulled off the carb and checked all the gaskets, there all good.

hellya

yep.....take your head off and double check..... you want the dot to the rear of the engine/exhaust port... installed the wrong way will also prevent proper gas flow

and when you reinstall the piston line up the ring like this..... then squeeze it together ...... then insert the piston into the head

maximus75

Well, I pulled it apart and my pstons has the dimple in the middle and a triangle to the side of it. I'm assuming they used this instead of the dot. It is lined up with the exhaust(got lucky) but i noticed the ring was stuck into the piston groove at one side. It has a tight fit on one part of the ring. I pulled the ring off and cleaned it up. I deburred it alittle so it would fit better and reassembled but still no go. One thing I did notice is that my baja with the stock 26cc has much more resistence when pulling the pull starter then this engine. Do you think I could have a defective ring? I also notice a small horizontial grove on the intake side at the bottom of the cyl that goes across the vertical groove which goes from the bottom of the cyl to a small hole. the stock cyl doesn't have this horizontial groove. Looks like it could be a scratch or something.

PAPE

Thought this might help

When I do compresion tests on my zenoah 26 I get 80-90 PSI depending on the head gasket (85psi stock)

also the split on the piston ring ALWAYS goes facing the intake port on these engines.

wan6176

couldne possible the simple dot coz the prob i had this problem too.wen i remove it was reverse.sumtime simple small ting are beyong our sight frommistake we learn to be perfect.

Kemo

some piston kits (just saying in general for any sort of piston in the engine world) dont have a clear dot... SO, with that being said, anything I rebuild, I use a sharpie and mark which side goes to the exhaust port on the new and old piston.

SPI pistons for snowmobiles went a while without this dot. My neighbor had her yamaha 600 rebuilt, and the guys put the pistons in backwards. It ran, but there was a nasty failure 5 miles into the break in.

wan6176

from wat i had experience all piston must have an indication .u cant go wrong unless ur too engross in doing it without reliase.

Kemo

the cool thing now is that instead of just a dot, you can find many pistons these days (not yet for CY) where it says EXH engraved on the piston and has an arrow pointing .

splcrazy

this has happened to me maybe three times , with the ring getting squashed in the ring groove in one side , its like the top of the piston hit the top of the cylinder smashing the top of the piston and making the ring getting jammed in the groove , to me it gives me suspision that the head was not properly machined to allow for the +2mm clearance , and sometimes it happened with the stock length crank also , to solve this i just used a 040 copper head gasket and never had a problem like that again , i always had problems like that when using the cy big bore kit 29cc, but since i got a proper name brand like ESP i can trust them that the clearance was cut for +2mm so i just used a 020 copper head gasket and no problems yet . BUT yeah when the ring got jammed in the groove it will never start but will FEEL like it has PLENTY of compression thats why we get tricked into
thinking that its something else rather than the piston , so like me , if you just put in another new piston it will fire up and work again untill it maybe happens again lol just remember to run more oil in your fuel mix then you usually would and it will help thats what i do .

maximus75

I definitly think its a compression problem. It just turns over way too easy. I don't think I had any head to piston interference but I do think either the ring or the pistion was not made right. Or maybe the bore was cut wrong and ruined the ring. I'm going to put the stock head back on and see what happens. If it fires up I'll have to see about getting the kit warranteed. Do you know what the stock needle setting are for the cy23? Thanks.

kidd

i remember an engine builder telling us here that some of the cy rings and heads don't match that well.

you should probably try another ring. just because it's cheaper and if you call the retailer they may just send you one

maximus75

Definitly something wrong with the kit. I put the stock one back on and she fired right up. And there is much more resistance when trying to start indicating much more compression. I'll have to call Dave's and have them send me another one.

TheFgMan01

^^ Good luck with that !!

clubin

I would check the diameter of the piston, it might be from a smaller displacement kit. Kinda makes sense, frustrating.

cyclops1970

My Feedback: (5)

indeed mistakes happen and if thats the case they'll do you right !

kryptonite5b

My Feedback: (-2)

i had the same problem with my headkit. this is what did to get it started. it seemed that it had fine compression but i was wrong. the ring was not true to the cylander. to fix that long enough for it to start, i just put about a little less then a soda cap of 2 stroke oil in the head thru the top of the spark plug port. roled around the motor so the oil would seat around the ring creating temperary compression. it was hard to pull for a about 2 yanks, then losened up and POP!! fired up. reved the snot out of it creating good back pressure around the ring and its been running ever since... just so you know, i spent about thirty bench hours and countless blisters pulling and checking every little thing, like spark, carb needles and wich way the piston was facing... the oil trick worked after 4 pull's!!

maximus75

This is true. It was a learning experience. The piston has a little play in the cyl but maybe the cyl was machined wrong, not sure. I can tell you one thing, I will be getting a compression testor this week. Thanks for the help everyone. I will use that trick on the new kit if I have any probs. I'm not takin this thing apart again until I have the new kit cause if I put the bb cyl in agian and it doesn't start I think my head might explode!!

splcrazy

lol if the ring got sqaushed in the groove and you managed to rip out the sqaushed ring and repair the groove for a new ring , it still wont start lol beleive me i tried already , the best way to fix it is put on a new piston kit with a thicker head gasket .

maximus75

The piston groove was fine, it was the ring that has a high spot on it. It was tight in the groove only on that spot on the ring. I tried to debur it but no go. I'm changing the whole thing out.