LMM: Rotating assembly ?

[ironmax]

Do you need the over bore because of the cylinder wall getting scored from the cracked piston? If so your build list is perfect for what you need. Did the other pistons have the same injector pattern on them? If not,That would be a good indicator of an injector problem being the culprit.


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[huey]

Yes, a cylinder was damaged. The cracked piston was really clean compared to the others and the pattern may be a little different. I think this is because I drove the truck 2 more miles to get off the interstate and it was up hill all the way. I’m going to have all of the injectors checked just to be safe. On a side note, the truck really ran good on 7 cylinders with all the oil it was burning.

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[S Phinney]

Usually if it was a injector that caused the problem you will see evidence of a different pattern from one of the
Orifices on the nozzle. Clean all your pistons good and you will see how symmetrical the patterns are.

You can see how the one orifice was not spraying correctly as the pattern is not close to the same as the others. This hole came from a bad injector.


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[huey]

I have been doing a little research on the Mahle pistons and here is my conclusion.

Mahle Clevite Cast;
Similar to an LB7
No coating
Stock height


Mahle Race Cast;
10 thousandths shorter to allow for decking the block
Coated skirts
Valve reliefs

I don’t think there are any other differences other than I did hear of the coating sometimes coming off. I think the casting process and material is the same but not sure.


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[ikeG]

Mahle makes their motorsports piston without valve reliefs too.

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[S Phinney]

There really isn’t a ton of research to do on cast pistons if you read a few threads or talk to a guy with real experience you will have your answer. I have not had any coating come off any pistons I have used so far. With that said, I I only use quality people doing the coatings. Fingers pistons for a cast piston will hands down be your best option. If you want more power down the road the performance Mahle cast pistons will break using compounds and higher hp. I didn’t have many problems until I started using them for higher hp than intended. So start by what you intend to do a go from there.


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[huey]

All I want is to pull my camper again and not crack another piston running the same mild tow tune like I did for the last 3 years. Fuel mileage and a long life is also important to me. I spoke to the guys at Mahle and they feel like the clevite cast pistons will be fine for what I’m doing. Everything I hear says the Mahle clevite cast without the bushings are at least stronger than my stock LMM pistons were. Please correct me if I am wrong so I don’t have to do this again. Thanks everyone.


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[ikeG]

If you are replacing all the pistons I would use mahle motorsports part # 930036055(std bore) or 930036075(.020" over). Most cost effective option that is also an improvement in strength. They come with pins and rings.

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[M.A.M.]

I’ve used the Mahle motorsports pistons in a few different LML cracked piston rebuild’s now, and have never had any issues out of them in over the road hot shot use. Fingers Pistons will definitely be strongest, but you lose some fuel mileage with them.


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[huey]

If you are replacing all the pistons I would use mahle motorsports part # 930036055(std bore) or 930036075(.020" over). Most cost effective option that is also an improvement in strength. They come with pins and rings.

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Don’t those part numbers have valve reliefs and also .010 shorter to allow for block decking ? Will that effect my milage and cold starts ?


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[ikeG]

The valve relief part numbers are 9300298xx. I would assume the fuel mileage difference wouldn't be a measurable amount

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[huey]

Are they actually stronger than the Clevite Cast ? If so what makes them that way ? Sorry for all the questions.

What I think I want is replacements that are dimensionally the same as my LMM pistons without the bushings and 0.020 over. This is why I keep comparing them to the clevite cast.


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[20dmax08]

How much fuel mileage is lost with fingers pistons?


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[M.A.M.]

It was noticeable, I’d say close to 1 mpg towing. On the other hand, if the quench is as tight as possible, and your tuner knows what he’s doing, it will be negligible. The tuner I had at the time didn’t.


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[Chevy1925]

Unless the machine shop is decking the block .010, I wouldn’t have the piston pre-cut at .010. Have the machine shop cut the tops of the pistons how ever much came off the block. Then upon assembly, measure protrution and keep piston to head clearance tight when picking a head gasket (somewhere in the .020-.024 range). This will help with mileage. Don’t get valve reliefs either.

Between keeping Mahle race cast, tight quench area and a good tuning, you should see comparable mpg you saw stock. Make sure piston to wall clearance stays tight too. DO NOT USE piston rings 41909, they are crappy sub part rings compared to stock. Make sure you get 42160 rings.

 

[huey]

Okay, great information. Is there a Mahle Race cast piston without the valve reliefs and are they stronger than the Clevite Cast ?



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[ikeG]

Either you are completely ignoring my posts or you do not realize that people refer to the motorsports pistons as "race" pistons. LOL

Here is the application and spec chart with the part numbers for all the motorsports pistons. http://www.us.mahle.com/media/motorsports/app-guide-2018-diesel.pdf

Botttom line, if you make sure your injectors are good, even the stock pistons would hold up well. But like i stated, if you are replacing all 8, no sense in putting stock back in.

 

[huey]

Yes I did realize they are one in the same pistons “Motorsports and Race”. The link you sent clears it up thanks ! I was quoted a difference of $600 dollars going from the Clevite Cast to The Motorsports Cast. Does that seem right ? One question I keep asking that has never been answered is; are the Motorsports Cast pistons actually Stronger than the Clevite Cast or at least the LMM stockers ?


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[ikeG]

Yes I did realize they are one in the same pistons “Motorsports and Race”. The link you sent clears it up thanks ! I was quoted a difference of $600 dollars going from the Clevite Cast to The Motorsports Cast. Does that seem right ? One question I keep asking that has never been answered is; are the Motorsports Cast pistons actually Stronger than the Clevite Cast or at least the LMM stockers ?


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The price difference is probably right. They have been the go-to piston for hundreds of engine builds for people. Aside from Finger's cast, these will be your strongest readily-available cast piston. Forged are not neccesarily maintenance free so they are not suitable for people putting miles on the engine.
I've personally ran the valve relief 930029895 pistons up to 1200 fwhp without a problem.

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[huey]

The pistons have been chosen:

Mahle Motorsports
Part number #930036075
Cast 0.020 over
No valve reliefs
No bushings
16.8 compression ratio
Coated skirt


Thanks for all the help. Hopefully I can crank out 425 trouble free horsepower for the next 200,000 miles.


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