low compression

nate_lohs · Post by **nate_lohs** » Wed Sep 06, 2006 9:20 pm

ok so i have had my spree running for a couple days now, i rode it to work today and i thought it was running great. couldnt exceed 30 mph tho on flat ground. i went and checked out a friend of mines spree and his started a lot easier and idled better and had a lot more pick up right when you take off. also i noticed a ticking noise that mine was making and his wasnt. it was very audible and i took the cover off of the alternator and found the ticking coming from the cylinder head. not sure if it had anything to do with spark or ignition, but i am running the plug thats supposed to be for extended riding. there was also a lot of carbon in the combustion chamger on the head, could that be causing the ticking?then i decided to check compression. i could not get over 50 psi, i tightened the adaptor as much as i could and it would not go over 50 psi. so i pulled off the head and the cylinder. headgasket looked pretty well intact, and the rings werent broken. looked like there were a lot of small scratches in the cylinder though. some i could feel with my finger nail if i went across them but just barely. color in the cylinder and on the piston seemed to change too.like some spots were silver and some spots more yellow. i removed the clip for the piston pin but i couldnt get the piston pin to come out. is there any trick to removing the piston?what i need to figure out tho is what my plan should be. i need to decide whether just to rehone and replace the rings or to get a new cylinder and piston? and how much play if any should the connecting rod have, i moved it side to side and could feel some play.

berreta22 · Post by **berreta22** » Wed Sep 06, 2006 9:42 pm

with care use a nut driver and put the square part on the pin and hammer it out. Do it lightly or you will bend the rod. There are clips at both ends but since you took out the clip on one end make sure you put the nut driver on the end that has the clip.(the head of the nut driver will clear the clip and make contact with the pin). If you have light scoring i think rings and a hone job should do the trick.

nate_lohs · Post by **nate_lohs** » Wed Sep 06, 2006 10:41 pm

ok i removed the piston.

this is what it looked like, and i here is what the cylinder looked like...

i can move the connecting rod side to side. there is no up and down play tho. what it looks like to me is that the small amount of play is allowing the piston to put pressure on the sides of the cylinder walls, the discolored spots. can anyone comfirm this?

berreta22 · Post by **berreta22** » Wed Sep 06, 2006 10:54 pm

how much side to side play is there? how is the needle bearing in the rod? (the part the piston pin goes through?)

nate_lohs · Post by **nate_lohs** » Wed Sep 06, 2006 11:07 pm

theres atleast 1mm possibly 1.5mm. i couldnt get a good straight down look while i was measuring but thats about it. i couldnt seem to find a spec for it. the needle bearing for the piston pin looks fine, all the needles are there. does it look like i could get away with leavin the rod bearing alone and just rehoning the cylinder and replacing rings or i what would you do in this situation?

nate_lohs · Post by **nate_lohs** » Thu Sep 07, 2006 8:04 am

i was looking through the service manual and came across specs for the crank.

connecting rod big end side clearance .5mm (0.02")
connecting rod big end radial clearance .04mm (0.002")

im guessing side clearance is what i was measuring. which was closer to 1.5mm would radial clearance be up and down play? in this situation im guessing i would need a new piston and new cyl. new rod bearings and possibly new rod. would it be cheaper just to buy another engine? the engine this is on has about 6k miles on it.

nate_lohs · Post by **nate_lohs** » Thu Sep 07, 2006 10:44 pm

ok i came to the conclusion that its a * little scooter so it doesnt have to be perfect. im just going to hone and rering and be done with it. yea the rod has just a little too much side to side play but whatever, i will post results hopefully next wednesday when i get my parts in.

berreta22 · Post by **berreta22** » Thu Sep 07, 2006 11:13 pm

you gotta remember that the rod may have side to side play..it doesnt mean that it wont run..but yeah, id just hone it and slap rings on it. Good luck!

nate_lohs · Post by **nate_lohs** » Thu Sep 07, 2006 11:25 pm

one more question i have that i couldnt figure out. the ticking coming from the cylinder head. could it be caused by carbon build up on the piston and in the combustion chamber? or could it be because im using the wrong spark plug? anyone experience this before?

berreta22 · Post by **berreta22** » Thu Sep 07, 2006 11:36 pm

could be both..use a wire brush and lightly get the carbon off..and the plug is bhp6s from ngk.. i know the 6 is right, not sure about the letter arrangement.

nate_lohs · Post by **nate_lohs** » Thu Sep 07, 2006 11:45 pm

i had the 8 in there when it was making the noise. i looked at my reciept from honda today and i forgot to mention which plug i wanted so they gave me the 4.

ejames81 · Post by **ejames81** » Fri Sep 08, 2006 7:25 pm

this is a valuable lesson to learn. every manual will tell you to decarbonize, but they are wrong about the interval. if you don't ever want this to happen to you again, decarbonize every 500 miles, or once a month, whichever comes first. that means simply removing the head, and getting the exhaust port. decarbonize the entire thing every two years, leaving the moped as if it was new.
if it was me, i would buy a new piston and cylinder. honing and measuring is a lot of work and requires experience, and discipline. not to mention vernier calipers, a micrometer, and the knowledge of how to use them.

nate_lohs · Post by **nate_lohs** » Fri Sep 08, 2006 7:41 pm

having to remove the head once a month seems a little extreme, although i am fairly new to 2 strokes, it just seems like overkill. buying a new piston and cylinder is a little more than i would like to spend on such a cheap scooter. honing isnt very hard and im not even going to bother measuring because i dont have any t gauges to measure the cylinder bore. with how cheap rings are ive already ordered parts and plan to just put it together and see what happens.

ejames81 · Post by **ejames81** » Sat Sep 09, 2006 3:39 pm

decarbonizing a spree is quite a bit more work than qt50, fa50, or express. there's plenty of plastic in the way.
hope the cylinder work pans out.

nate_lohs · Post by **nate_lohs** » Tue Sep 12, 2006 9:30 pm

well i picked up all my parts tonight. got it all together and its running pretty good. checked compression again and its at about 130 psi now, much better than the 50 psi before. everything is good except i cannot seem to exceed 30 mph. when i had it all apart i filled my exhaust up with carb cleaner and just let it soak over night and then rinsed it out with water thinking it might help but its still pretty heavy. havent weighed it but i know its more than 3 lbs. has anyone ever tried using solvent to clean it out? i really would like to find a way around using a torch but if it comes down to it i will. anyone have any exhaust cleaning tips or know where to buy a new exhaust that wouldnt require being decarbonized?