Plugging oil holes in pistons

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#1
Why would I want to do this?

2 stroke piston for bridged ex port used in non bridge barrel.

Hence 2 small holes leaking at TDC.

Probably not making a difference, but would be nice to find out by closing them.

But what can I block them with that isn't going to cause damage if it falls out? Too scared to weld it.
 
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#2
I think buying a new piston would be the best solution. They don't last forever, anyways. Is this piston out of another bike? Why are the holes already drilled? Pistons expand and contract too much for me to be confident with epoxy. Welding will do all kinds of bad things and require the piston be re-machined. The performance difference between having the holes and not is probably similar to having a slightly relaxed petal on the reed valve. It makes it a little harder to start, but doesn't really affect too much when the engine is up to speed.
 

RedBull

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#3
I wouldnt do it Im sure besides like 76GMC said with all that expanding and contracting i would be afraid that they help also with stres much like the gaps in sidewalks, bridges, and building that help concrete move around. but if you wanted to you could mabey throw some belzona in their then polish it smooth with a super fine sand paper?
 
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#4
Any good tig welder should be able to weld them without distorting the piston. Weld them from the inside. :cool:
 
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#5
RedBull said:
I wouldnt do it Im sure besides like 76GMC said with all that expanding and contracting i would be afraid that they help also with stres much like the gaps in sidewalks, bridges, and building that help concrete move around. but if you wanted to you could mabey throw some belzona in their then polish it smooth with a super fine sand paper?
Have you seen what Belzona costs? He might as well buy 2 new pistons.
 

RedBull

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#6
lol i have no idea i got a bunch of it for free
 
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#7
It's like $200 a pound. It's good stuff, though. I know someone who used it to repair a 7000 hp diesel engine that put a wrist pin though the side of the engine block, twice. Pielstick, quite possibly the worst large diesel ever made.
 
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#8
Rivets....

Do not try to weld on pistons. It is not about distorting them, it is all about taking the heat treat out ot them. When you weld aluminum, it goes back to the T-0 conditon. Dead soft.

Buy some aluminum countersunk solid aluminum rivets. Countersink the outside of the piston and peen them over on the inside. File off flush on the outside.

Good luck

Michael
 
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#9
Racer D-1 said:
Do not try to weld on pistons. It is not about distorting them, it is all about taking the heat treat out ot them. When you weld aluminum, it goes back to the T-0 conditon. Dead soft.
Michael

While it is true extensive welding on aluminum will change the heat treat, a small oil hole sealed by a tig welder will do little to change the heat treat on the skirt itself. I have tig welded many, many pistons. Two stroke pistons to change the transfer port timing and many four stroke pistons to raise the compression. Before the piston manufactures started making high compression pistons, tig welding is how we raised the compression on our pistons. Of course, certain proceedures and precautions are taken to keep the piston cool when doing extensive welding. I have run many welded pistons in dirttrack and road race engines with no failures.

Just my $ .02
 
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#10
Thanks for the suggestions guys, just to clarify it is a brand spanky new piston, just the best for the application I could find bar the holes. May look at both options using an old piston to trial.
 
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#11
You are not losing compression. The oil holes are below the rings. You may lose a little charge out the exhaust, but it wont be enough for you to notice
 
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#12
That's weird, I was notified about this post about a week ago & couldn't see it. :think:


84cr500lover has just replied to a thread you have subscribed to entitled - Plugging oil holes in pistons - in the Mods & Performance Forum forum of Dirt Rider . Net Forums.

This thread is located at: http://www.dirtrider.net/forums3/showthread.php?t=150925&goto=newpost

Here is the message that has just been posted:
***************
The holes do not affect compression at top dead center, the holes are below the rings. Think about it. The holes are there to force some oil onto the bridge on the down stroke.
***************

Ahh slightly different.


Yes I know won't lose any chamber compression but will lose a little crankcase pressure & charge. Will it make any difference? Probably not much, but who knows?

A friend was building an engine that wasn't performing as well as he hoped, turns out he ran a piston that didn't cover the port at top dead centre (skirt was a bit narrow for wide bridged port) & changed piston & it 'came alive'.

ok bigger holes in his case, but same scenario, -am I losing a 1/10 of an hp total?- or needlessly giving away 2 or 3 in the midrange? Don't know. Would like to trial it on the dyno. Must send that old piston to friend to weld.
 
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#13
Welding should be OK if done carefully. I do not think you will have any issues at all with a welded set of holes.

Chris
 
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#14
Thanks, I hope to test, weld & retest on dyno if I can arrange it properly.

Anyway, hello Cujet, long time. Did you ever build that monsta RZ engined dirtbike? Just embarking on a Cheetah engined RZ roadbike. (well, ordering bits)
 
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#15
No RZ engined dirt bike. I think the RZ engine is too large physically. I am much more likely to try a sabertooth cylinder on a CR250 or CR5. It looks like those are pushing 100HP.

I am not able to find an answer about using the Sabertooth cylinder on anything other than a TRX 250.

Chris