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  1. #1

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    Overbore - how far can u go on the stock sleeves?

    I have a 4tec motor that the flywheel bolts sheared off on. I was sold the motor as perfectly running for $2500 only to find this out later. Maybe I'll make a post about the seller that scammed me, I should... Anyhow apparently after this the motor apparently sat for some time. I pulled the head and the cyl's were frozen in place, and it had su8rface rust on all the exposed cyl wall areas. Long story short, I'm not going to be able to hone out the surface rust, and have to rebore the block. Which brings me to my question.

    How much can you overbore the OEM sleeves and still retain the needed strength? I read that the 104mm overbore kit from PPG requires re-sleeving of the block. Is 101mm safe? 102mm? CP is making me pistons, so I can request whatever size I like. I was wanting to go 102mm, but what is the max racers go before changing the sleeves??

    SO... I was curious what peoples experiences were with running oversize pistons in an OEM block, and if anyone knows how much you can safely overbore the OEM sleeves without sacrificing strength? or needing a re-sleeving? I suppose the basic rules of strength of metals states that the thinner the the object, the less force it can absorb. But whats the most that is recommended to overbore the OEM sleeves?

    Any and all advice experience with over boring is appreciated, thanks!!


  2. #2

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    I bet if you hone it .001" it'll clean up... unless it's pitted up bad.

  3. #3
    Water4fire's Avatar
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    Quote Originally Posted by engineermike View Post
    I bet if you hone it .001" it'll clean up... unless it's pitted up bad.

    Sorry I have to disagree. The Motror I got from Savage had the same issues and the rust did not hone out. The block need to be bored 1st over. The rust from sitting is just a mess on everything. I am not sure on how far you could bore, but I know the type of mess you are referring too.

    How much are the CP pistons?

    /

  4. #4
    First overbore is approx. .010. Then you can use the Rotax pistons.

    Mark

  5. #5

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    Boostaholic--Did you buy this motor from Savage??

  6. #6
    GTXX's Avatar
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    IMO you're not going to gain enough power from going larger bore to make it a worth risking shortening the life of the engine. Re-sleeving is not something easily done, the sleeves have to be machined out, and from what I've heard doesn't run much better after a lot of money and work. I would go to std. oversize .021mm and not look back.

  7. #7

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    Well here's my story...

    My Dad picked up a Vulcan 500 a couple years ago. The bike was given to him because it went under salt water in Gulfport, MS during hurricane Katrina. It sat for a year, so the engine and transmission were totally frozen up.

    We disassembled it and found that every steel part was rusted up. Being that the bike wasn't worth very much, it would be totaled if you bought all new bearings, gears, chains, etc... We proceeded to painstakingly clean all the rust off the bearings, chains, and gears with a wire brush and carburetor cleaner. The only parts that were beyond repair were the pistons since we broke them while beating them out of the rusted up cylinders.

    We re-assembled it using all the old parts except for the pistons. We bought a pair of used pistons with used rings off e-bay. We ran a dingle-berry hone through the cylinders and went back together. After changing the oil 3 times in the first 10 miles, it cleaned up. The bike ran fine for a long time and didn't even smoke or use oil.

    For father's day, I bought him a used set of Ninja 500 cams for it, which made a night-and-day difference in power. I drag raced a brand new Intruder 900 with it and won, but that's all beside the point.

    The point is... rust usually looks a lot worse than it is. A mass of steel increases in volume by a factor of 12 when it turns to rust. So, a cylinder can look bad at first, but when you run a hone through it you'd be surprised how much base material is intact. Furthermore, some small pits left behind won't hurt anything. On a 4" bore, you can take out 0.001" material (maybe more) without hurting anything. We usually build race small-block Chevy's .001 loose anyway.

    Mike

  8. #8

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    Quote Originally Posted by engineermike View Post
    Well here's my story...

    My Dad picked up a Vulcan 500 a couple years ago. The bike was given to him because it went under salt water in Gulfport, MS during hurricane Katrina. It sat for a year, so the engine and transmission were totally frozen up.

    We disassembled it and found that every steel part was rusted up. Being that the bike wasn't worth very much, it would be totaled if you bought all new bearings, gears, chains, etc... We proceeded to painstakingly clean all the rust off the bearings, chains, and gears with a wire brush and carburetor cleaner. The only parts that were beyond repair were the pistons since we broke them while beating them out of the rusted up cylinders.

    We re-assembled it using all the old parts except for the pistons. We bought a pair of used pistons with used rings off e-bay. We ran a dingle-berry hone through the cylinders and went back together. After changing the oil 3 times in the first 10 miles, it cleaned up. The bike ran fine for a long time and didn't even smoke or use oil.

    For father's day, I bought him a used set of Ninja 500 cams for it, which made a night-and-day difference in power. I drag raced a brand new Intruder 900 with it and won, but that's all beside the point.

    The point is... rust usually looks a lot worse than it is. A mass of steel increases in volume by a factor of 12 when it turns to rust. So, a cylinder can look bad at first, but when you run a hone through it you'd be surprised how much base material is intact. Furthermore, some small pits left behind won't hurt anything. On a 4" bore, you can take out 0.001" material (maybe more) without hurting anything. We usually build race small-block Chevy's .001 loose anyway.

    Mike
    Good story! I bet the damn thing would run forever Get a good hone on it and new pistons....it would Blowup.

  9. #9
    rxpxseadog's Avatar
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    Quote Originally Posted by boostaholic View Post
    I have a 4tec motor that the flywheel bolts sheared off on. I was sold the motor as perfectly running for $2500 only to find this out later. Maybe I'll make a post about the seller that scammed me, I should... Anyhow apparently after this the motor apparently sat for some time. I pulled the head and the cyl's were frozen in place, and it had su8rface rust on all the exposed cyl wall areas. Long story short, I'm not going to be able to hone out the surface rust, and have to rebore the block. Which brings me to my question.

    How much can you overbore the OEM sleeves and still retain the needed strength? I read that the 104mm overbore kit from PPG requires re-sleeving of the block. Is 101mm safe? 102mm? CP is making me pistons, so I can request whatever size I like. I was wanting to go 102mm, but what is the max racers go before changing the sleeves??

    SO... I was curious what peoples experiences were with running oversize pistons in an OEM block, and if anyone knows how much you can safely overbore the OEM sleeves without sacrificing strength? or needing a re-sleeving? I suppose the basic rules of strength of metals states that the thinner the the object, the less force it can absorb. But whats the most that is recommended to overbore the OEM sleeves?

    Any and all advice experience with over boring is appreciated, thanks!!
    Boost,

    Please identify the ass that cheated you -- we rely on people to be honest about what they're selling on this forum.

    Sorry, to hear about your misfortune.

  10. #10
    GTXX's Avatar
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    Quote Originally Posted by rxpxseadog View Post
    Boost,

    Please identify the ass that cheated you -- we rely on people to be honest about what they're selling on this forum.

    Sorry, to hear about your misfortune.
    yeah!

    I tried selling a motor for less than that and couldn't because I would not simply say that it was in good running condition, because I didn't know. It turns out after taking it apart there is nothing wrong, just that I didn't know and wouldn't lie about it.

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