2015 - Project Rocket Kart #2

[Desertduler]

I have a serious problems this cylinder is not sliding down easily on the pistons it keep getting stuck I need help

What size piston rings did you buy? What are the numbers on the top of the pistons crowns both of them? Did you insert the piston rings in the cylinders before you installed them on the pistons and check the end gap of them while they were in the cylinder bore? Do you know what the cylinder bores are? I ask these questions first as a process of elimination.

 

[rushking19]

The bore is 64.5 mm the piston rings I ordered is 64.5mm for the Rotax 399cc which is my motor, unless I got sent the wrong one, and I didn't have the tool to check end gap but I did put the piston rings in the cylinder to check,there are no numbers on the pistons, and the strange thing is that it went on easy on the first and second piston rings but then after that I just stopped and got stuck and I can't get the cylinder off now I put oil in the cylinder and let it soak to see if it will loosen up so I can take it off

 

[Desertduler]

The bore is 64.5 mm the piston rings I ordered is 64.5mm for the Rotax 399cc which is my motor, unless I got sent the wrong one, and I didn't have the tool to check end gap but I did put the piston rings in the cylinder to check,there are no numbers on the pistons, and the strange thing is that it went on easy on the first and second piston rings but then after that I just stopped and got stuck and I can't get the cylinder off now I put oil in the cylinder and let it soak to see if it will loosen up so I can take it off

64.5mm is the standard bore for that engine and that engine has a right left pistons that need to be in their correct locations when the cylinders are installed if not the end gaps of the piston rings can be exposed to a open port and protrude out into the port and break, do you have the pistons in their correct locations and or the cylinders in their correct location? Did the cylinders slip down on the pistons easily? Did you make sure the end gaps of the piston rings were oriented on the locating pins on the pistons?

 

[rushking19]

Yes I do the mark is pointing to the exhaust port like its supposed to and before this I made sure that it did come near any ports and plus the piston rings haven't even reached the ports and there already stuck

 

[Desertduler]

Yes I do the mark is pointing to the exhaust port like its supposed to and before this I made sure that it did come near any ports and plus the piston rings haven't even reached the ports and there already stuck

Both the right and left pistons have an arrow that points towards the exhaust,that engine has a twisted cylinder configuration and the pistons are also twisted to align with the cylinder porting,look at the bottom of the pistons and you will see that they have an open area just off the centerline of the wrist pins,those open areas of the pistons have to line up with the transfer ports in the cylinders and if they do not then you have broken the piston rings and you have problems.

---------- Post added at 04:12 PM ---------- Previous post was at 04:10 PM ----------

Can you post any pictures of the bottom of the stuck cylinders and pistons?

 

[rushking19]

Here, I'm puzzled only thing I could think of is that I was sent the wrong rings and I think it's to late to return them

 

[Desertduler]

Here, I'm puzzled only thing I could think of is that I was sent the wrong rings and I think it's to late to return them

You have the piston in the correct location,I would say you have oversized piston rings in the standard bore,anchor the engine down and yank on the cylinder real hard,never force a cylinder on a piston,they should slip right on with light pressure.

---------- Post added at 04:37 PM ---------- Previous post was at 04:31 PM ----------

One other thing is if just by chance you did not have the end gaps of the rings on the pins in the ring grooves you could have broke a piston ring and that will jam the piston in the cylinder.

 

[rushking19]

I don't think so I made sure I tried and same thing happened to the other side of it but I was able to pull the other side out

 

[Desertduler]

I don't think so I made sure I tried and same thing happened to the other side of it but I was able to pull the other side out

Ok, take the set of piston rings off of the piston that is free and put a piston ring in the cylinder squarely and see if there is any end gap,(clearance) between the ends of the piston rings,if the end gaps touch and or you can't fit the piston ring in the cylinder squarely then you have oversized rings. The piston rings should have the size marked on them on the side that faces upwards.

 

[rushking19]

There over sized I knew it now I have to buy new piston rings because someone else messed up I'm starting to get afraid Im not going to finish it in time before the build contest ends

 

[Desertduler]

See this picture of this set of piston rings? These are stamped 73 which means that they are for a 73mm bore,your piston rings should have 64.5 marked on them.

 

[Desertduler]

There over sized I knew it now I have to buy new piston rings because someone else messed up I'm starting to get afraid Im not going to finish it in time before the build contest ends

Yup,wrong piston rings,what does the cylinder look like now and the piston ring lands and grooves?

---------- Post added at 05:52 PM ---------- Previous post was at 05:48 PM ----------

Don't ever trust someone else is giving you the correct parts,when ever you are building an engine check,check and double check everything,you have learned something by this.

 

[rushking19]

They look fine, only thing is now I can't find any on EBay that is std size, I'm starting to wonder how much will it be to over bore it, I'm guessing it might be 0.10 or 0.20 over, but I'll have to find out to be sure, I can't think of any other way to fix this outgrew than over boring it out

 

[Desertduler]

I also would check to make sure that the bottoms of the cylinders are not spread out and or cracked at the transfer port openings in the cylinder, if they are then those cylinders are junk,sorry just being honest.

---------- Post added at 06:01 PM ---------- Previous post was at 06:00 PM ----------

They look fine, only thing is now I can't find any on EBay that is std size, I'm starting to wonder how much will it be to over bore it, I'm guessing it might be 0.10 or 0.20 over, but I'll have to find out to be sure, I can't think of any other way to fix this outgrew than over boring it out

If you were to bore the cylinders then you will need new oversized pistons.

 

[rushking19]

I forgot all about that I'll just have to keep searching for the std size

 

[Desertduler]

And if I may state one more time that I would most certainly make sure that the bottoms of those cylinders are not spread from having those oversized piston rings forced into them,if they are spread and or bell mouthed out the engine will have excessive piston skirt to cylinder wall clearance at B.D.C. and the piston skirts will shatter in time because of this it will be the end of your engine,do not try to fool yourself into thinking that they are fine without checking them because that will be a bigger mistake in the long run than then the one that has already occurred.

 

[rushking19]

Ok I'll check it out tomorrow I'm tired and it's getting dark

 

[Desertduler]

Ok I'll check it out tomorrow I'm tired and it's getting dark

Ok,sounds good,I am not trying to be jerk I am just trying to help you out.

 

[rushking19]

I know I know I have a plan tho I have a plan

---------- Post added at 08:38 PM ---------- Previous post was at 08:24 PM ----------

But first I have to get this piston un stuck I poured oil into the cylinder and I'm going to let it soak a few days then try to pull it off

 

[Poboy kartman]

And if I may state one more time that I would most certainly make sure that the bottoms of those cylinders are not spread from having those oversized piston rings forced into them,if they are spread and or bell mouthed out the engine will have excessive piston skirt to cylinder wall clearance at B.D.C. and the piston skirts will shatter in time because of this it will be the end of your engine,do not try to fool yourself into thinking that they are fine without checking them because that will be a bigger mistake in the long one than then the one that has already occured.

OH....SHUT UP!!!! .....Nobody likes a wise guy!!!!!

Well....actually....around here .....WE DO!!!

Carry on.....