TRX250R.ORG
Workshop => Engine and Bottom End => Topic started by: ATV_Chick08 on March 21, 2014, 11:09:13 PM
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Ok, I thought it would be pretty strait forward to order a piston kit, but apparently not. I'm rebuilding the top end on my 88 because it's past due. I had my guy at the Honda shop check out the cylinder and piston, and he told me to replace it with the same .25 Pro X piston that's in it, however I can't seem to find one...
I'm gathering that the standard piston size is 66mm, is that correct? So I need a 66.25? The markings on the inside of the piston are CR25088, but even when I look for a piston for a CR 250 I'm not finding a 66.25. I've got to call Duncan Racing to order reeds and packing kit for my silencer but they aren't open again til Tuesday. They don't even have the piston kits listed now, it says to call for availability. I just looked the other day and it said they were $129.99 which seemed a little high.
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No that price is the norm. Loren bored my national ported cyl and found a woessner piston kit for it for the same price. I used to work at a cycle shop and a Wiseco was $49.99 so I really feel the prices are rediculous these days. I'm not familiar with the sizing any more, sorry I'm not any help
(http://i83.photobucket.com/albums/j300/Dezsled/37374536e0f7e9492a495af6e38a653d.jpg)
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No that price is the norm. Loren bored my national ported cyl and found a woessner piston kit for it for the same price. I used to work at a cycle shop and a Wiseco was $49.99 so I really feel the prices are rediculous these days. I'm not familiar with the sizing any more, sorry I'm not any help
Maybe Duncan's not using Pro X pistons now, it's been 3 or 4 years since they rebuilt my 88 motor. The Honda shop could only get a .50 over Pro X piston. Somehow in owing a 250R for 18 years I've managed to never have to order a piston kit. I don't want to get something different without knowing for sure what I need. Hopefully Duncan will have the Pro X or something equivalent.
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I'm rebuilding the top end on my 88 because it's past due. I had my guy at the Honda shop check out the cylinder and piston, and he told me to replace it with the same .25 Pro X piston that's in it.
If your top end is past due and its got a .25 over in there then you need to get the next size up and go to .5. Or is he saying it is stock and you need to just go .25 over?
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I was told that it's not like in the hay day when everything was trx250r. Loren said he would have locate a piston kit for me and he normally uses only certain brands. It's not like the manufacturers are going to have xxxx quantity of each size made any more. I have afew new oem pistons laying around but it's 85-6 stuff.
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Breezy,
For the 87 to 89 cylinders, a Wiseco 66.25mm piston kit, is a number 526MO6625, but being on the STD bore, you really need to have the cylinder bore measured to be sure that 66.25mm will be big enough. Normally on the first time boring the cylinder, they will be worn enough that it will need to be taken to the 66.50mm size, to clear up the wear in the bore.
Now LA Sleeve offers a Pro-x cast piston in a 66.25mm, a part number 4321 piston kit, but after that size it is a Wossnor brand, part number 8189D050 , 66.50mm kit. My new catolog, does not list any larger sizes of the Pro-x cast piston larger than a 66.25mm, but LA probably still has larger sizes of the Pro-x pistons on hand, just not listed in this new catolog I have.
For the OEM TRX cylinders, you cheapest route for a new piston is on e bay, just find the right size your needing.
The new Wossnor forged or the Wiseco would be best to use, leave the cast piston for stock play engines.
Neil
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Thanks for the info guys. We took the cylinder and piston to the Honda shop and had the one mechanic look at it. He's been there for years and has a 250R. He checked it out, looked at the piston and rings, and measured everything,and he said it didn't need bored. The piston that came out of it is a Pro X .025. The mechanic said that it looked good and just needed a ball hone run through it. He said they don't do honing any more and they take it to a local Harley shop or Car Quest.
I originally bought the cylinder new in 96 when I bought the quad. It was freshened up once when I was racing back then. Here about 3 years ago I sent the whole motor to Duncan to be rebuilt, and I'm going to assume that Loren is the one that took it up to .25.
When I say overdue, I just mean that I haven't really ridden the 88 much since I got the 86 set up for the woods. I only raced the 88 once or twice last year and didn't notice it was down on compression and power until I had the 86 motor rebuilt. There's nothing wrong with it, per se. I'm freshening up the Duncan motor so I have the 88 as a back up for the GP series.
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Breezy,
For the 87 to 89 cylinders, a Wiseco 66.25mm piston kit, is a number 526MO6625, but being on the STD bore, you really need to have the cylinder bore measured to be sure that 66.25mm will be big enough. Normally on the first time boring the cylinder, they will be worn enough that it will need to be taken to the 66.50mm size, to clear up the wear in the bore.
Now LA Sleeve offers a Pro-x cast piston in a 66.25mm, a part number 4321 piston kit, but after that size it is a Wossnor brand, part number 8189D050 , 66.50mm kit. My new catolog, does not list any larger sizes of the Pro-x cast piston larger than a 66.25mm, but LA probably still has larger sizes of the Pro-x pistons on hand, just not listed in this new catolog I have.
For the OEM TRX cylinders, you cheapest route for a new piston is on e bay, just find the right size your needing.
The new Wossnor forged or the Wiseco would be best to use, leave the cast piston for stock play engines.
Neil
526MO6625 is 0.25 mm oversize for the 1985 and 1986
562M06625 is .025 mm oversize for the 1987 through 1989
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...............,and he said it didn't need bored. The piston that came out of it is a Pro X .025. The mechanic said that it looked good and just needed a ball hone run through it. He said they don't do honing any more and they take it to a local Harley shop or Car Quest.
I am troubled by the experience level of someone that recommends using using a ball hone.
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526MO6625 is 0.25 mm oversize for the 1985 and 1986
562M06625 is .025 mm oversize for the 1987 through 1989
Now figure that out. I was sitting there looking directly at the part number in the catolog & still put it in wrong. What is it called, that sickness you can get when you reverse numbers & put down words was suppose to be put in later.
I've just got this fixation on any TRX250R engine build, that its any year TRX cylinder, long rod crank, a spacer plate & old model 85/86 piston kit, so I guess the old model number came out even though I was looking at the new model piston kit.
Its just kinda abnormal, to me anyways, to see a 250R engine put together with all the parts that go together from each year model
I'll 2X on the ball hone idea. Most things have a place to be used, leave those ball hones to the auto industry.
Neil
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I'll 2X on the ball hone idea. Most things have a place to be used, leave those ball hones to the auto industry.
Neil
So are you guys saying that you should never hone a cylinder, but bore it every time you change the piston and rings? Both the Honda mechanic and the guy in the shop at car quest said the cylinder looks great. They are going to hone it (with something other than a ball hone) and mic it and make sure everything is to spec before I order a piston. The guy at car quest recognized the quality of the work done to the cylinder and commented on it, he seemed to be very knowledgable.
It also seems to no one makes the .25 piston any more but Wiseco, this is according to the guy at LA Sleeve. So as long as the cylinder is true I'm either just going to have to replace the rings on the Pro X piston or make sure Wiseco has the .25 kit. There web site says they do, but they were already closed before I could call.
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The guy who was going to hone the cylinder doesn't feel like he has the equipment or whatever to do it right, and no one makes a .25 over piston any more. I talked to Loren Duncan and I'm sending everything back to him and let him decide whether or not it needs bored.
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...................I'll 2X on the ball hone idea. Most things have a place to be used, leave those ball hones to the auto industry.
Neil
I would not use a ball hone to clean sewer pipe. A good hone will only touch the high spots and remove minor imperfections. A ball hone makes the cylinder look a little better but follows all imperfections, making any bore it touches worse.
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So are you guys saying that you should never hone a cylinder, but bore it every time you change the piston and rings? Both the Honda mechanic and the guy in the shop at car quest said the cylinder looks great. They are going to hone it (with something other than a ball hone) and mic it and make sure everything is to spec before I order a piston. The guy at car quest recognized the quality of the work done to the cylinder and commented on it, he seemed to be very knowledgable.
It also seems to no one makes the .25 piston any more but Wiseco, this is according to the guy at LA Sleeve. So as long as the cylinder is true I'm either just going to have to replace the rings on the Pro X piston or make sure Wiseco has the .25 kit. There web site says they do, but they were already closed before I could call.
If the bore looks good and measures within spec it should not need to be honed. Anytime a cylinder is honed some material is removed from the bore, making the piston to cylinder wall clearance a little looser. If your air filter does it's job and you run a lot of oil in the fuel it is not uncommon to be able to replace the piston many times without boring the cylinder. If you hone the cylinder each time you replace the piston you will have to bore it more frequently.
Pistons need to be replaced frequently to keep the clearances tight. Keeping the clearances tight makes the bore last much longer and the engine will produce more power. Some of the seasoned racers understand this but the average guys lets the clearances get too loose and damages the bore requiring boring the cylinder to the next oversize each time the piston is replaced.
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How often do you recommend changing the piston? I had Eric Gorr port my cylinder and bore it. He sent the piston with it it is a 66.25 wiesco. It is on an 85 atc.
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If the bore looks good and measures within spec it should not need to be honed. Anytime a cylinder is honed some material is removed from the bore, making the piston to cylinder wall clearance a little looser. If your air filter does it's job and you run a lot of oil in the fuel it is not uncommon to be able to replace the piston many times without boring the cylinder. If you hone the cylinder each time you replace the piston you will have to bore it more frequently.
Pistons need to be replaced frequently to keep the clearances tight. Keeping the clearances tight makes the bore last much longer and the engine will produce more power. Some of the seasoned racers understand this but the average guys lets the clearances get too loose and damages the bore requiring boring the cylinder to the next oversize each time the piston is replaced.
Thanks for the reply, I appreciate the information. I bought this cylinder new from Duncan in 1996, and then they rebulit the whole motor a few years ago. I need to do a better job of keeping track of the hours on this rebuild. I didn't realize that it was down on power until I had my 86 rebuilt and had something to compare it to. I don't know enough about it to decide whether or not to replace the piston without it needing honed or bored. I should have just sent it back to Loren to begin with.
I am also curious as to how often it is recommended to change the piston. It's not like I get to go out and ride for hours and hours. I only race, and even then I don't put a lot of hours on my motors.
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How often do you recommend changing the piston? I had Eric Gorr port my cylinder and bore it. He sent the piston with it it is a 66.25 wiesco. It is on an 85 atc.
If your using a 66.25 piston and plan on using that size again you might want to try to pick one up on Ebay because no one makes them any more. It's annoying that these web sites show that they have them, then you call and find out they aren't available. Wiseco shows it being available to order, but when I called the guy acted like I should have know they don't make them anymore.
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Thanks. I had it done yr and half ago and haven't put a lot time on it. I only rode it some last year. I will pick up another one.
Sent from my LG-US780 using Tapatalk
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I am also curious as to how often it is recommended to change the piston. It's not like I get to go out and ride for hours and hours. I only race, and even then I don't put a lot of hours on my motors.
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Pistons and rings will run much longer than the times I have listed below before your piston will be fatigued enough to fail. My recommended times below are for the ones racing or want their engines to always be running within 98 to 100% of their peak potential.
Most 250 sized single cylinder engines using OEM cast pistons that are producing around 45 RWHP will need the ring/rings replaced about every 3 to 6 hours. OEM cast pistons should be changed every other ring/rings set change to keep the clearances tight and piston fatigue in the safe zone. I see some 45 hp engines that need their rings replaced every hour or less because the engine builder did not know how to properly shape the exhaust port and or put the correct port chamfers on all of the ports.
On 250 size single cylinder engines producing 50 to 60 RWHP the pistons and rings need to be replaced more frequently than the times mentioned above because of the wider ports and higher RPMs that are associated with engines in this power range.
For 250 size engines using forged pistons the above time on rings is about the same as when using cast pistons. The forged pistons tend to collapse and get loose much more quickly than cast pistons and may need the piston and ring/rings changed at each scheduled ring change.
The 310 and up big bore kits usually use forged pistons and will typically collapse even more quickly than the 250 sized forged pistons. Forged pistons are much less prone to catastrophic piston failures than cast pistons when they get real loose. Cast pistons require the piston clearances to be kept tighter than forged pistons to avoid high fatigue levels which eventually result in cracked pistons and eventually catastrophic piston failure.
My experience has been that cast pistons will usually produce a little higher power average than the forged pistons and can be subject to longer periods of full throttle without the piston crowns overheating.
The above recommended piston and ring changes are based on .....no dirt is getting past the air filter and a lot of oil is being used in the fuel.
The above results were patterns we observed over the years of frequently dynoed engines from many racers as their engines accumulated time from day to day and week to week racing. If you look at the owners manual of any of the CR, KX, RM, or YZ 250s built during the last 15 to 20 years they were produced, you will see that the factory engineers found similar recommended piston and ring changes due to ware/power losses for their 40 to 45 HP motocross engines.
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cast pistons work fine until they go tits up. then you have a big mess http://www.thumpertalk.com/topic/1072142-seized-engine-in-my-01-cr250-today-where-to-begin-pics-coming/