Piston Questions

JimmyHoffa · 05-26-2007, 10:19 PM

I have a stock 400ex block, with a FMF Hi-flow header and Titanium 4 can. I have recently realized that my ATV is slow. However, I need to know what sacrifices I'm gonna be making here. I was planning on either JE's 11.5:1 - 415cc piston or Wiseco's 11:1 - 416cc piston, in combination with a longer duration cam, like Hotcam's Stage 2 deal. (I'm getting a XR400 head gasket too.)

I was talking to a guy at the track with a 450r (That I got to ride!) and he claimed that the Honda Service Manual recommended getting a new piston every 20 engine hours. That's a joke. Do 400 dudes have to do this too if the get a decent piston? I don't have the money for that. I do all my own work, and spend outrageous amounts of time doing crap like getting tires off of rims by myself all in the name of cash. If I get a solid/mild block together as specified above, and ride mainly only on the weekends and bomb around at the local track, can I expect to get several years out of my baby-before a teardown?

Tigmaster is currently living at my house for a few days and doesn't get to answer this. We're devouring a powersporting sandwich! A little break-in bread Sunday, the JuIcY MeAt of the Richwoods track on Monday, and possibly another satisfying loaf of Finger Lakes State Park on Tuesday. I'm going to get sore. Real sore. (It may be just a open-faced sandiwich if we can't make it to Columbia. Got the ole' fingers crossed.)

wr250f95 · 05-26-2007, 11:11 PM

My wr has never been rebuilt, ever! its an 01. Im not sure if your bikes a kick or electric start. If its kick and you put a higher compresion piston in it, it will naturaly be harder to kick. If its an electric than the strain on the starter will be greater. I think that as for all the the 20 hour new piston stuff its if you want it to be at its best all the time.

JThompson · 05-27-2007, 02:47 AM

Tig is my technical guy

. I will say i never did any piston work on my yz400f for 2 years and it was still fine when i sold it... And I raced every weekend. Never seemed to have a compression issue. These were not short races either I am talking enduros 70+ mile rides.

gscx · 08-22-2007, 10:00 PM

you probly could get a few years out of it. But you should probly try to replace the piston at least once every 2 years. especially if your riding it hard. Just dont wait to long and have the damn thing shatter in your cylinder like it did on my 04 yz-125. it happened at my local track and it was the shortest day of riding ive ever had...

wr250f95 · 08-23-2007, 07:26 AM

I take that back the crank shaft broke

but i rebuilt it with a 13.5:1 piston

tigmaster · 08-23-2007, 08:12 PM

lol, 13.5:1 is a good ratio. thats wat i run.

wr250f95 · 08-23-2007, 08:48 PM

ya, it just broke from metal fatigue, the weak point was found

tigmaster · 08-23-2007, 09:19 PM

lol wow, i cant believe that it had a weak spot.

05-26-2007, 10:19 PM	#1 (permalink)
JimmyHoffa C Rider Join Date: Jan 2007 Location: east central MO Posts: 27 iTrader: (0)	Piston Questions I have a stock 400ex block, with a FMF Hi-flow header and Titanium 4 can. I have recently realized that my ATV is slow. However, I need to know what sacrifices I'm gonna be making here. I was planning on either JE's 11.5:1 - 415cc piston or Wiseco's 11:1 - 416cc piston, in combination with a longer duration cam, like Hotcam's Stage 2 deal. (I'm getting a XR400 head gasket too.) I was talking to a guy at the track with a 450r (That I got to ride!) and he claimed that the Honda Service Manual recommended getting a new piston every 20 engine hours. That's a joke. Do 400 dudes have to do this too if the get a decent piston? I don't have the money for that. I do all my own work, and spend outrageous amounts of time doing crap like getting tires off of rims by myself all in the name of cash. If I get a solid/mild block together as specified above, and ride mainly only on the weekends and bomb around at the local track, can I expect to get several years out of my baby-before a teardown? Tigmaster is currently living at my house for a few days and doesn't get to answer this. We're devouring a powersporting sandwich! A little break-in bread Sunday, the JuIcY MeAt of the Richwoods track on Monday, and possibly another satisfying loaf of Finger Lakes State Park on Tuesday. I'm going to get sore. Real sore. (It may be just a open-faced sandiwich if we can't make it to Columbia. Got the ole' fingers crossed.) __________________ 2003 400ex. Complete overhaul. Pro Armor nerfs and bumper. PC black frame. Razr rears, w/fronts to come. FMF Hi-flo header coupled to a Titanium 4 can. Front shocks, bars, swinger skid and filter pending. Ask me anything. I've touched all the bolts.

05-27-2007, 02:47 AM	#3 (permalink)
JThompson Administrator Join Date: Aug 2006 Location: Bellingham WA Posts: 4,900 iTrader: (5)	Tig is my technical guy . I will say i never did any piston work on my yz400f for 2 years and it was still fine when i sold it... And I raced every weekend. Never seemed to have a compression issue. These were not short races either I am talking enduros 70+ mile rides. __________________ Tired of ads? Become a member for an almost ad free site! Also we give away monthly prizes just for posting! Register today! Looking for places to ride! Want to review a riding area? Check them out! PRE-ORDER MOTOTIPS Stickers now. Help keep mototips running! Get your order in today! Buy NOW! Special Discounts for members only! Check out our new discount forum for retailers offering to help you save money! Mototips Discounts

08-23-2007, 07:26 AM	#5 (permalink)
wr250f95 Super Moderator Join Date: May 2007 Location: New Mexico Posts: 7,827 iTrader: (1)	I take that back the crank shaft broke but i rebuilt it with a 13.5:1 piston __________________ "LIFE'S JOURNEY IS NOT TO ARRIVE AT THE GRAVE SAFELY IN A WELL PRESERVED BODY, BUT RATHER TO SKID IN SIDEWAYS, TOTALLY WORN OUT, SHOUTING'...HOLY S**T... WHAT A RIDE!" this, is why I ride.

08-23-2007, 08:12 PM	#6 (permalink)
tigmaster Administrator Join Date: Aug 2006 Location: Missouri, United States Posts: 7,526 iTrader: (1)	lol, 13.5:1 is a good ratio. thats wat i run. __________________ --'03 CRF450r-- --FMF Pipe, Pro-Tech Revavle-- --Vortex Basket With Tusk Disks And HP Springs-- --Pro Taper Triple Clamps And Bars-- --Devol Full SP With Moose HGs-- --Renthal 13/50 With R1 Chain-- --Now It Is The End, Probably...-- --'06 CBR F4I-- --Bone Stock-- Check Our Latest How-To Here

08-23-2007, 08:48 PM	#7 (permalink)
wr250f95 Super Moderator Join Date: May 2007 Location: New Mexico Posts: 7,827 iTrader: (1)	ya, it just broke from metal fatigue, the weak point was found __________________ "LIFE'S JOURNEY IS NOT TO ARRIVE AT THE GRAVE SAFELY IN A WELL PRESERVED BODY, BUT RATHER TO SKID IN SIDEWAYS, TOTALLY WORN OUT, SHOUTING'...HOLY S**T... WHAT A RIDE!" this, is why I ride.

05-26-2007, 11:11 PM	#2 (permalink)
wr250f95 Super Moderator Join Date: May 2007 Location: New Mexico Posts: 7,827 iTrader: (1)	My wr has never been rebuilt, ever! its an 01. Im not sure if your bikes a kick or electric start. If its kick and you put a higher compresion piston in it, it will naturaly be harder to kick. If its an electric than the strain on the starter will be greater. I think that as for all the the 20 hour new piston stuff its if you want it to be at its best all the time.

08-22-2007, 10:00 PM	#4 (permalink)
gscx Pro Mototips Member Join Date: Aug 2007 Location: bridgeville DE Posts: 2,228 iTrader: (0)	you probly could get a few years out of it. But you should probly try to replace the piston at least once every 2 years. especially if your riding it hard. Just dont wait to long and have the damn thing shatter in your cylinder like it did on my 04 yz-125. it happened at my local track and it was the shortest day of riding ive ever had...

08-23-2007, 09:19 PM	#8 (permalink)
tigmaster Administrator Join Date: Aug 2006 Location: Missouri, United States Posts: 7,526 iTrader: (1)	lol wow, i cant believe that it had a weak spot. __________________ --'03 CRF450r-- --FMF Pipe, Pro-Tech Revavle-- --Vortex Basket With Tusk Disks And HP Springs-- --Pro Taper Triple Clamps And Bars-- --Devol Full SP With Moose HGs-- --Renthal 13/50 With R1 Chain-- --Now It Is The End, Probably...-- --'06 CBR F4I-- --Bone Stock-- Check Our Latest How-To Here

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