mahle pistons

[iluvmy4g63]

can anyone help me out? whats the math fourmula from metric bore size to standard. i have a new set of mahle pistons that are file-to-fit. it says bore x .0045'' for top ring bore x .0055''. second ring. my bore is 85.5 mm. how do i brake this down to get a standard mesurement in inches from a metric bore size.

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thanks for your help

 

[bastarddsm]

i don't mean to be an ass, but if you cant figure this out, you probably shouldn't be builing your own engine. look up a conversion table. 25.4mm = 1 inch 85.5mm/25.4 = 3.366" 3.366*.0045 = .0151"
3.366*.0055 = .0185"


Also I think you may have this backwards. Generally you want more clearanse on top becuase it is hotter.

 

[iluvmy4g63]

i don't mean to be an ass, but if you cant figure this out, you probably shouldn't be builing your own engine. look up a conversion table. 25.4mm = 1 inch 85.5mm/25.4 = 3.366" 3.366*.0045 = .0151"
3.366*.0055 = .0185"


Also I think you may have this backwards. Generally you want more clearanse on top becuase it is hotter.

nope. its your top compression ring you want best seal possable. i knew what it was just realy needed a second opion. all the top rings are perfect out of the box. second ones need filed. witch in this case are all going to be .0190''

 

[bastarddsm]

is that what mahle says with the rings? You may want to cunsult with a serious engine builder. It might be different in the case of a high perfomance turbo engine...

 

[iluvmy4g63]

it has a chart that came with the pistons. a clearance table.if your running nitrous up to 150hp. nitrous over 150hp, blown gas, blown alcohol. exp. street,strip. bore x .0045 top. bore x .0055 second ring the for nitrous under 150 hp your top ring is bore x .0060 second is bore x .007. blown alcohol is bore x .0055 top bore x.0065 second. yea but iam going to call mahle before i file anything. i have rebuild 10 stock blocks this is my first forged block so iam going to make sure i take my sweet time and triple check everything.

 

[pneumo]

The reason to have a wider ring gap on the second ring is so any pressure that gets past the top ring will escape from the gap between the rings. Otherwise, high pressure below the first ring causes it to flutter and not seal as well at high rpm.

 

[Burnett03]

i don't mean to be an ass, but if you cant figure this out, you probably shouldn't be builing your own engine. look up a conversion table. 25.4mm = 1 inch 85.5mm/25.4 = 3.366" 3.366*.0045 = .0151"
3.366*.0055 = .0185"


Also I think you may have this backwards. Generally you want more clearanse on top becuase it is hotter.

I don't mean to be an ass, but you are totally wrong about more clearance on top because it is hotter.. Also some people aren't good at math, but can build an engine with their eyes closed.

 

[90laserRSfwd]

don't you guys file fit your rings anyway? I do mine on a per cylinder basis with snap on feeler gauges? Maybe I'm just off my rocker today though

 

[iluvmy4g63]

i have always file to fit . this is the first time i needed a math to find a gap clearance though.

 

[RipperXX]

Some one correct me if I am wrong but this is my understanding from what I have read.


Taking measurements at the top of the cyl and filing your rings to fit there will result in better compression, but later on in the engines life like 100,000 miles later result in lower compression than it would have had, had it been done like normal?

I know this is an old race engine trick but it was my understanding it wasn't really a good thing to do on an engine you planned on using long term.


Please correct me if I am wrong because I would like to know.

 

[bastarddsm]

The reason to have a wider ring gap on the second ring is so any pressure that gets past the top ring will escape from the gap between the rings. Otherwise, high pressure below the first ring causes it to flutter and not seal as well at high rpm.

I stand corrected. I think it varies by application, my wiseco I put in my (4stroke) VMX bike wanted a larger clearance at the top then second ring.

 

[iluvmy4g63]

Some one correct me if I am wrong but this is my understanding from what I have read.


Taking measurements at the top of the cyl and filing your rings to fit there will result in better compression, but later on in the engines life like 100,000 miles later result in lower compression than it would have had, had it been done like normal?

I know this is an old race engine trick but it was my understanding it wasn't really a good thing to do on an engine you planned on using long term.


Please correct me if I am wrong because I would like to know.

good qustion. i was told buy a very good engine builder. (sean glazer) that you want to check ring gaps in the block rite about were the rings are at TDC. making sure the gaps are at the same place that they are going to ride on the piston.also square them in the block. use the piston to do that.and check with a feeler gauge. what do you mean buy normal? like not fileing? they file rings from the factory. your rings getting old and worn out should be the only reason you will lose compression. but then again i have seen bad cly. grooves at TDC that are bad enough to cause blow buy and change compression.

 

[RipperXX]

When I said "normal" I was talking just above mid stroke.

It was my understanding on a normal engine you measure for the rings from about mid stroke to a little above that. It is my understanding that filing them from measurements taken at the top of the cyl will cause excessive ware. Hence later on in life less compression.


And here I would like to say I am no engine builder, I am just going off of what I have read and heard from other techs.




I bring all this up just to point out something IFI am correct. And IF I am then wouldn't it make more sense to just use a custom/higher compression ratio piston and file the rings like normal? Besides unless I am wrong filing them this way will only gain a few psi more.

Which makes since on a race engine were mod's may be restircted and or you want to stay in your class but get every last hp you can. But may not really make sense on a street build.

 

[iluvmy4g63]

yea, i have heard both ways also. but i think iam going to pay more attention to a guy(sean) who has bin running his 1-g dsm in the mid 8's sence 2001. then a guy who has only built v-8's or everything but a 4g63-t. his quote saying is mesure 3x before you cut 1x. also you have to remember that comp.ratio's can very on ring gap,how deep the dish on your pistons are, the height of your head gasket. just to name few. also just to let ya know. i only build engines for fun. iam ok at what i do. but iam bearly scratching the surface compaired to some of the fellas on this web site. everybody has there oun way of doing things. my advice to you with engine building is just take your sweet time.

 

[blazebolt]

Sorry to bring this thread back up. I emailed Mahle about piston gaps and they told me:

top = 0.017"
second = 0.016"
oils are okay out of the box

Does that sound right? According to the spec sheet that it came with as stated in the first post. Top = bore x .0045" and second = bore x .0055"

 

[pneumo]

Sorry to bring this thread back up. I emailed Mahle about piston gaps and they told me:

top = 0.017"
second = 0.016"
oils are okay out of the box

Does that sound right? According to the spec sheet that it came with as stated in the first post. Top = bore x .0045" and second = bore x .0055"

Something's backwards. The top gap should be tighter than the second gap. Top ring gap = Bore x .0045" = .015"
Second ring gap = bore x .0055" = .018", assuming a 85.5mm bore/ 20 over.

 

[blazebolt]

Here is the latest response from Mahle. Anyone have any comments?

The instructions are misleading. This sheet is in all of the Powerpak kits. Most are domestic engines, used for street or dirt track racing. They don't have to worry about emmissions, or use turbos.
Use 0.017" top and second gaps. That's 3.366" x 0.005".
This will have the effect of tightening up the top more, because it's closer to the heat. Kinda the same thing, but not as pronounced.
The gap on the second should be tight enough to control oil, but allow excess pressure thru, to maintain top ring seal.

 

[My1GLaser]

I did mine at .018 top and .021 2nd on Wiseco pistons. 6000 HARD miles with 25-30 psi of boost, 50-75 track passes and still have perfect compression. (185-190) Use the motoman break-in method, although I know that is a little off topic.

I researched for weeks before I decided on a ring gap. There is a consensus to set the 2nd ring slightly looser so pressure doesn't get stuck between the rings and cause flutter and other issues.

 

[iluvmy4g63]

Here is the latest response from Mahle. Anyone have any comments?

The instructions are misleading. This sheet is in all of the Powerpak kits. Most are domestic engines, used for street or dirt track racing. They don't have to worry about emmissions, or use turbos.
Use 0.017" top and second gaps. That's 3.366" x 0.005".
This will have the effect of tightening up the top more, because it's closer to the heat. Kinda the same thing, but not as pronounced.
The gap on the second should be tight enough to control oil, but allow excess pressure thru, to maintain top ring seal.

iam not sure were you got this info. but right out of the box my rings have more clearance then that. there about 19.0''(top) and second rings are about 15.0''.
i left the top rings as is . and filed the seconds to 24.0'' it might burn a little oil but iam going to be in the 22-28 psi range. so a lil oil burn ant to bad.

 

[blazebolt]

My information came directly from Mahle. Also, what is your ptw clearance? If yours is bigger than what he suggested (.0015"-.0020") then that could also explain the higher ring gap.

 

[iluvmy4g63]

My information came directly from Mahle. Also, what is your ptw clearance? If yours is bigger than what he suggested (.0015"-.0020") then that could also explain the higher ring gap.

there at about .003'' i had it bored to 85.5mm
the mahle piston have built in ptwc.
i think what happened is the paper is for standard(85.mm) and sence mine is 20 thousands (85.5)over that could change ring gaps.