I tore down my srx because the comp. was only 110 per cylinder and had the local yammi expert check the piston to cylinder clearance and it is .008 and my manual says it should only be no more than .004 anyway he said the pistons collapsed and if I replaced them that it would do it again with Yamaha pistons..? I have never ever used non-OEM parts in engines because I figured they were the best. Has anyone had good luck with Wisco or non-oem pistons in thier SRX....Thanks
x2ryder
New member
I have never had a problem with wisecos. But I am sure this thread will have many opinions.
I would be willing to bet the reason they are worn is from never having rings replaced and the sled has over 5000 miles. You cant beat the OEM yamaha powder forged pistons, they are very strong and durable, they dont expand at nearly the same rate as the wiseco's do and with the thicker oem rings last alot longer and provide better sealing due to the piston clearances and bore stability. But like any 2 stroke engine ever made they need rings changed on regular intervals, about every 2500-3000 miles and the pistons will last a long,long time.
Tha sled has 4000 miles on it and the pistons don't have any vertical marks at all.....thay look really good but the Yammi guy said that the pistons collapsed (shrank ) and that its pretty common...thats why i'm wondering if another set of OEM pistons will do the same thing.?
vibeline
New member
shrunken pistons
I have come to the conclusion that in time the pistons do shrink in diameter and grow a bit in length. (I have documented it).
There is alot of jerkin goin on in there.
I have a set right now out of my srx in the same state.
(about .006" clearance) I am gonna try coating the skirts. (.001" per side)
Only the front and back. I will post pictures when they are done.
If you measure the pistons just below the wrist pins you will find they are still in tolerance. If you coat the whole piston they will be to big.
The pistons only shrink so far then they start to wear because of the rocking front to back.
If you can still see the machining marks on the skirt they have shrunk.
If the skirts are shiny about 1/2" from the bottom they are worn.
call your local hotrod shop ask them who does hightech coatings.
(moly-disulphide)
I have come to the conclusion that in time the pistons do shrink in diameter and grow a bit in length. (I have documented it).
There is alot of jerkin goin on in there.
I have a set right now out of my srx in the same state.
(about .006" clearance) I am gonna try coating the skirts. (.001" per side)
Only the front and back. I will post pictures when they are done.
If you measure the pistons just below the wrist pins you will find they are still in tolerance. If you coat the whole piston they will be to big.
The pistons only shrink so far then they start to wear because of the rocking front to back.
If you can still see the machining marks on the skirt they have shrunk.
If the skirts are shiny about 1/2" from the bottom they are worn.
call your local hotrod shop ask them who does hightech coatings.
(moly-disulphide)
ExpertXViper
New member
mrviper700 said:
Don, seems like you explain this issue every week and its the same thing over and over again.
valin
Active member
If you are going to rebuild, go with the OEM pistons. Nobody builds a better piston. The Wiseco's (Wisqeako's) expand more and too quickly, and larger clearances are required when running them. The newer Wiseco's are alot better that the older stuff, mind you. I've heard good things about the SPX pistons, and know of a few people who have run them in Cat's and were very impressed with them. I do not know of anyone who has run them in a Yammy though. Stick to OEM.
vibeline, the reason you will find the measurment at the bottom of wrist pin is not worn because they dont wear there, its the pivot point, they are worn on the bottoms of the skirts because when you run worn out rings on them they lose stability in the bore and begin to rock back and forth and this eats up the skirts, and lets blow by seep into the fresh intake charge in the crankcase. This is the black you see on the sides of the pistons below the second ring. You will also see this black on the bottom of the transfer ports where its reinhaling blow by exhaust.
A friend owns my original 98 srx I bought new, it has 7800 miles on it now, still original pistons, mind you it has had 3 sets of rings in its 7800 miles too!! Just was in there last year and pistons check out to perfect spec! Keep rings in them like your supposed to and they will run a long time with optimum output!
If some of you guys think thats too often to rering a 2 stroke, check out a 2 stroke factory dirtbike factory service suppliment and look at the timetable(hours) they recommend ring replacement, its for a reason!!!
A friend owns my original 98 srx I bought new, it has 7800 miles on it now, still original pistons, mind you it has had 3 sets of rings in its 7800 miles too!! Just was in there last year and pistons check out to perfect spec! Keep rings in them like your supposed to and they will run a long time with optimum output!
If some of you guys think thats too often to rering a 2 stroke, check out a 2 stroke factory dirtbike factory service suppliment and look at the timetable(hours) they recommend ring replacement, its for a reason!!!
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daman
New member
Your yammi expert isn't much of an expert then, OEM yammie pistons are
very good like what's stated above, Always OEM over aftermarket in a
yammie IMO.....
very good like what's stated above, Always OEM over aftermarket in a
yammie IMO.....
ExpertXViper
New member
Like Don said about the dirt bike thing. My 2000 Honda CR250 manual says replace PISTON and RINGS every 3 races or 7.5 hours. Do I do that no cause my bike is only for trail use and doesnt get the abuse compared to a race bike. I replace rings every 2-3 years pending how much use it gets each year. Running 44:1 premix, when its calls for 32:1 and never had a problem. But you will if you dont pay attention to your outside temps and your jetting. Learned that the hard way when I first bought the bike.
Dont be stubborn listen to Don, the man knows his sh** and stick with OEM products. Aftermarket companys dont always obey factory specs and tolerances.
Dont be stubborn listen to Don, the man knows his sh** and stick with OEM products. Aftermarket companys dont always obey factory specs and tolerances.
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