would leaking intake manifold cause this???

[Fatcat 1]

I was wondering if a leaky intake would cause a drop in compression or this strictly a worn ring issue? oh yeah its on a KX 125 2003. Also I wanted to know since it is the first time its been apart since brand new if I could get away with using a stock size piston and rings again without a hone or a bore job? or would a re sleeving be in order. IT has that wacky space age nickasil lining on the cylinder
Thanks

[KDXGarage]

Loss of compression can be caused by a leaky intake. It can also cause a seizure. If you haven't had a 125 taken apart within the almost 6 years it has been around, you really need to do it.

Plated cylinders are the norm. Iron or steel, or whatever, is the old style.

You are basically asking us if we can look inside your engine and see the condition of the cylinder walls. The answer on that is no.

The cylinder was not sleeved when stock.

[Fatcat 1]

You are basically asking us if we can look inside your engine and see the condition of the cylinder walls. The answer on that is no.

Uhh...That is impossible without a picture or you being at my house I just wanted to know IF the cylinder wasn't all scored and damaged IF I could use a stock size piston and rings for a replacement OR would I have to bore it to a larger size or re sleeve it to make it work? Yes I know the cylinder came factory with the nickasil lining not bare metal.
Thanks for the input and am looking forward for more info!

[Chris420]

If the cylinder is to the manufactures specifications than you can just stick a new piston and rings set in. However I would just order a new cylinder and piston to match and rebuild the entire top end. Reason I say this is because you probably need to go through the exhaust valves, operating rod, and power valve system and clean them all up. Also you can send the old cylinder out and have it resleaved for when you do this again later so you dont have any significant down time on your bike.

[KDXGarage]

If the bore is damaged or worn, then I suggest replating. Here's a quote from the service mnaual (you did buy a service manual, right?),

"If any of the cylinder inside diameter measurements exceeds the service limit, the cylinder must be replaced with a new one since the PLATING cylinder cannot be bored or honed."

Someone needs to inspect and measure the piston and cylinder dimensions.

[Fatcat 1]

Yes I do have a factory service and repair manual with that exact statement in it. I have bore gauges and mics and most any tool at my disposal. With the exception of some of the specialty tools designed for motorcycles. So determining the usefulness of the cylinder won't be a problem.

I would just order a new cylinder and piston to match and rebuild the entire top end

Where is a good place to get a new cylinder? (besides the dealer of course)

[Chris420]

Moto Sport has the best prices and most of the time they have the parts in inventory. They wouls also give you free shipping. Make sure to order the Athena complete gasket kit it is the cheapest and best way to go for the gaskets. You will spend most of your time getting the the timming right. Dont rush it when it comes to timming make sure that is perfect otherwise you will destroy the entire engine. Also make sure you put the piston on the connecting rod properly one guy on this forum put it on backwards and destroyed the engine. Follow the manual step by step and everything will go great and the knowledge you gain will help you in understanding how the engine operates. After you break it in your next step is jetting and that is an entirely different beast.

[Fatcat 1]

Here are some photos that should produce some opinions. The cylinder is smooth from top to bottom and all the way around no scoring or vertical grooves there is some vertical marking as you can see but they cant be felt or catch when I inspected it.

[Chris420]

Looks like it is in perty good shape. Why did you tear the engine apart? I would measure everything first just to make sure. Also check the decking on the cylinder head. Put a ruller on the cylinder head and slide the currect fealer gauge under it to make sure it is two speck. A warped cylinder head could cause a loss in compression. You can also slightly get a high compression by sanding the cylinder head down a little but if you have not done that before I would not attempt it.

[Fatcat 1]

I will post some photos of the piston it wouldn't let me upload any more. I mic'ed
the cylinder and all the top end components everything is between standard and spec limit so I am going to replace these parts with stock standard size 54 mm parts so they should fit just fine on the exsisting cylinder bore by the next time I need a rebuild I should be able to afford the full meal deal on the cylinder

[Fatcat 1]

Here is a link to some photos of the cylinder and piston:
Motorcycle pic pictures from friends & fun photos on webshots
THe piston has a flat spot on the front where it has rubbed against the exhaust port divider which I think is from a worn out wrist pin bearing when I mic'ed the pin it was below tolerance hence allowing the piston to ride against the front of the cylinder causing the flat spot in the ring and piston thus causing low compression. No severe damage was done to the cylinder as you can see the lower crank bearing has absolutely no play in it and is tight as a drum!!

[KDXGarage]

The thin bridge in pictures 3 and 4 looks heavily worn. Am I seeing that correctly?

Is the piston missing a chunk out of it??

[Fatcat 1]

If the thin bridge is the part directly under where the rings meet in the photos yes there is a chunk missing. it looks like it was burnt through more so than it having broken off. There is no scoring or wear at that point on the cylinder but you can see where it was due to the combustion of the engine. as stated earlier the cylinder is smooth as all get out with no scoring damage. I think had I kept riding the bike it probably would have had severe damage. But it was the first time I rode it after I bought it and it wouldn't even pull the front wheel off the ground so I knew something was wrong. The guy I bought it from also said he was having trouble getting the carb jetted properly.....Well low compression and you will be chasing proper jetting until the top end is repaired!!

[Fatcat 1]

Chris and KDX thanks for the tips and replies to my thread here as well!!

[QKENUF4U]

1. ya need to have a REAL MACHINIST look at the cylinder cause i see some things i would be worried about (gouges) plus ya need to make sure its still ROUND (cylinders wear oblong-egg shape)
2. leaky intake will NOT AFFECT compression since the piston/rings/transfer ports are above the intake during compression
3.if it needs re-plated just do a google search and send it off
4. make sure the bottom end bearing is still good also. NO UP/DOWN MOVEMENT FROM ROD ON CRANK !!! side to side is normal.

[Fatcat 1]

. ya need to have a REAL MACHINIST look at the cylinder cause i see some things i would be worried about (gouges) plus ya need to make sure its still ROUND (cylinders wear oblong-egg shape)

I would venture to say that an experienced industrial engineer of 43 years would probably have the normal shop machinist handled! I would also go out on a limb and say that he is a REAL MACHINIST and has a full blown shop in his 6 car garage!! the cylinder has been inspected by him and he has given it the green light to reuse without replating or replacing (oh yeah hes my father inlaw)

The Main journal bearing on the crank is very tight no play at all up and down and like you said it has just a little bit side to side.

as for the gouges you see there are none. The photos are deceiving as the cylinder is smooth all the way around and from top to bottom!

[QKENUF4U]

well there ya go then. put a new piston/rings in it and ride. check your ring end gap before ya put it back together (.003-.004" per inch of bore)

[Fatcat 1]

Thanks there quick!!
what is the best method to adjust the ring end gap if needed? Being that the cylinder is broken in I would imagine I wouldn't have to widen the gap my only concern will be the possibility of having to narrow the gap!! but the cylinder is within spec so I guess I will wait until I get all the replacement parts and find out!

I am ordering the complete Wiseco Top End Kit from Motosport.com (standard size piston)