Lubrication holes in piston skirts good idea or not.

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graham heise
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Lubrication holes in piston skirts good idea or not.

#1 Post by graham heise » Sun Aug 20, 2017 7:11 am

I have read in a 2 stroke tuning manual about the benefits towrds piston and bore longevity by adding lubrication holes to piston skirts. I took a photo of area's marked on a spare piston where the holes should be drilled, inlet side 2 at 2mm exhaust side one at 3mm. Looking for the foughts on thisImage Image

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Re: Lubrication holes in piston skirts good idea or not.

#2 Post by T.RexRacing » Sun Aug 20, 2017 11:08 am

Don't see the need after tearing my '84 apart a few times. Only time I've seen a real need is on big bore singles with bridged exhausts where heat is the prime factor in lubrication deficiencies. IMO it's easier to use more oil.
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Re: Lubrication holes in piston skirts good idea or not.

#3 Post by hondaror » Sun Aug 20, 2017 11:58 am

I am with T on this one. Don't see a need or a benefit if you are running the RZ as it was intended, stockish.
I'm not a fan of large oversize big bore twins, as they just don't behave like the RZ was intended to. So I can't even comment on the need in this situation.
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Re: Lubrication holes in piston skirts good idea or not.

#4 Post by graham heise » Mon Aug 21, 2017 3:11 am

Thanks for the reply gents. can see your piont. I have 10000k's on a set of wossner pistons that will soon get a re ring.. the pistons and bores in that engine don't show any adverse wear. In another engine i'm building the cyclinders came with wiseco pistons that are recieving new rings.. as i said read it in a 2 stroke tuning manual and the writter said with the added oil holes the pistons won't have the typical dark or seized exhaust skirt area. It sounded like it held merritt and considering the old wiseco prone to seize reputation i thought it might be worth a try. Can't see how it could do any harm except cracks forming around the hole.

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Re: Lubrication holes in piston skirts good idea or not.

#5 Post by T.RexRacing » Mon Aug 21, 2017 12:43 pm

Wiseco pistons are prone to intolerance of use. Fit them properly and let 'em warm up before giving 'er the whip and all is good. They've always been good stuff but cannot be treated to gas and go like a cast piston.

I am a proponent of more oil=more power+longer engine life. I typically get 'round 15K miles(24K KM) per pistons set,two piston sets per bore job and 20K (32K KM) miles per crankshaft. I use a liter per 600 miles (1K KM) of Amsoil Interceptor via pump under hard use. The cranks have some life left when I rebuild but it's cheap insurance IMHO to build not break.
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Re: Lubrication holes in piston skirts good idea or not.

#6 Post by Bare » Wed Aug 23, 2017 9:04 pm

As above... Oil is cheap insurance...why be miserly with it.
:-) Martin K was a Big proponent of drilling piston holes for "lubing' purposes.
AFAIK He was the only one pushing this idea though.

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Re: Lubrication holes in piston skirts good idea or not.

#7 Post by T.RexRacing » Wed Aug 23, 2017 10:22 pm

I don't see it as a negative. Just never seen the need on small bore bikes.
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Re: Lubrication holes in piston skirts good idea or not.

#8 Post by mboddy » Thu Aug 24, 2017 1:06 am

Yamaha does it on the TZR250 and TDR250. I do it on my RDLC 250 and 350 race bikes.
2mm diameter holes between exhaust port and transfers. 10mm below lower ring land and 15mm below that.
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Re: Lubrication holes in piston skirts good idea or not.

#9 Post by graham heise » Fri Aug 25, 2017 6:53 am

more good replys. i wouldn't consider it necessary in a stock or tuned road bike but maybe in a race bike that spends it's life in the top end of the tacho, i think it being beneficial. I don't see it as a fix for incorrect jetting or ignition advance but an opportunity to allow more oil to reduce wear in the slim area in the cylinder wall outside of the port area. I've read that the suzuki 2t mx teams would scuff (reverse hone) there pistons to keep more oil betwwen the skirts and cylinder.
I see the lodgic of, run more oil from the pump or premix but then i remember a conversation i had with a succesfull Australian production class endurance racer from the 70's. Murray Hill told me he would run the premix pump lean, atf in trans and pass the other rd400's down the straight.
Bare yes it was martins tuning manual i read about this mod and i thought it had merritt. Although in his manual it suggests a lube bore 50mm bellow the crown in the exhaust side skirt. this bore would be inside the exhaust port at tdc which i think would lead to a drop in crank case pressure? Mboddy i think has the ideal area for the bores, ie between exhaust port and transfers. I'm still considering this mod for a track bike 31k engine.
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Re: Lubrication holes in piston skirts good idea or not.

#10 Post by Bare » Sun Aug 27, 2017 4:04 pm

~12 Years ago, after having perused Keitch's 'book' I asked Scott Clough about drilling Piston holes .
He suggested ignoring the ' book'.
Noting that Scott has been consistently racing and winning on Yama 350's since '73..
the advise was in the very least .. 'experienced'

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Re: Lubrication holes in piston skirts good idea or not.

#11 Post by RZtuner » Tue Aug 29, 2017 5:54 pm

Some of the worlds top two stroke tuners frequently drill lube holes in pistons, especially on bridged exhaust ports. You just have to be careful where you place them. It's even a recommended procedure on many Wiseco pistons.
http://www.wiseco.com/PDFs/Manuals/MSeries.pdf" onclick="window.open(this.href);return false;

I highly recommend Martin's tuning manual, it is packed with very detailed and GOOD information. Martin probably knows more about RZ's than 99% of the punters and wanna be experts on this site.
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Re: Lubrication holes in piston skirts good idea or not.

#12 Post by T.RexRacing » Tue Aug 29, 2017 11:14 pm

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Re: Lubrication holes in piston skirts good idea or not.

#13 Post by kenny » Wed Aug 30, 2017 6:32 am

I have heard that 1 hole with 2 dimples under it holds the oil in the dimples for better protection.

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Re: Lubrication holes in piston skirts good idea or not.

#14 Post by MK » Wed Aug 30, 2017 3:16 pm

Finally someone saw my true colors shining through humor & sarcasm :-)

Concerning "normal" lubrication holes:
Pro: Lubrication
Con: Notch effect on small dia bores may lead to skirt failure.

What Graham was referring to is a pic of a piston lubrication hole in the center of the exhaust side which is open to the duct in TDC (#3 in the first post).
I saw that in an engine prepared by Armin Colett (THE RD500 pope in Germany, unfortunately he deceased a few years ago) and rated it as could work / has to be tried out. It certainly will loose a bit of crankcase compression but it shouldn't be too much - likely not noticeable in a road bike.

I always wanted to check it with a sim - maybe time to use my rusty old engMod2T again.
Last edited by MK on Wed Aug 30, 2017 4:05 pm, edited 1 time in total.
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Re: Lubrication holes in piston skirts good idea or not.

#15 Post by MK » Wed Aug 30, 2017 3:58 pm

Here you go.
Checked a Std RD350 YPVS @ 4500, 6000 and 8000. The curves show the relative pressure in the exhaust port and the crankcase.
If pressure at crank is higher than at the port you'll have a flow of fresh air/fuel escaping to the exhaust.
The hole is in contact with the port maybe around +/-30 deg around TDC, so that's the only region you need to check.

And here everything is pretty save: Most time the port pressure is above crank which means no danger of "loosing" fresh charge. The lubrication takes place before and around BDC when crank pressure is high.
pressure_8000.png
pressure_8000.png (43.63 KiB) Viewed 7274 times
pressure_4500_6000.png
pressure_4500_6000.png (50.02 KiB) Viewed 7274 times
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