Rebuilding an m20b25. Got questions.

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Re: Rebuilding an m20b25. Got questions.

Postby Yoshi » Wed Oct 29, 2014 12:41 pm

Anyone else it looks a bit like a dick?

Yea... i wouldn't reuse that piston.
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Re: Rebuilding an m20b25. Got questions.

Postby 87e30 » Thu Oct 30, 2014 12:29 am

Wow. Only you would notice that. :-D
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Re: Rebuilding an m20b25. Got questions.

Postby M20_fever » Thu Oct 30, 2014 2:45 am

That piston is trashed. Remember it's cast, so all those damaged areas are now huge stress risers. The structure of the piston face is compromised so it should be replaced. Stock pistons are cheap on the forums. Sometimes people will just give them away.
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Re: Rebuilding an m20b25. Got questions.

Postby 87e30 » Thu Oct 30, 2014 12:12 pm

I've heard of people using Toyota pistons in m20's. Anyone have any experience with that?
Schwarz 5-speed 87 325is (newest project)
Arktisblau 5-speed 86 325e (current DD)
Schwarz 5-speed 87 325e (parts car/LS1 swap?)
Gazellenbeige automatic 85 318i (70,000 miles)
Alpine white 5-speed 87 325is (my first e30, possibly for sale)
99 Suburban
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Re: Rebuilding an m20b25. Got questions.

Postby Yoshi » Thu Oct 30, 2014 3:20 pm

Would not do.
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Re: Rebuilding an m20b25. Got questions.

Postby 87e30 » Thu Oct 30, 2014 6:38 pm

Care to expand on that in any way? I've heard the Toyota pistons are much stronger than the BMW ones for a LOT less money. I forget which engine they are out of, I probably have it bookmarked somewhere.
Schwarz 5-speed 87 325is (newest project)
Arktisblau 5-speed 86 325e (current DD)
Schwarz 5-speed 87 325e (parts car/LS1 swap?)
Gazellenbeige automatic 85 318i (70,000 miles)
Alpine white 5-speed 87 325is (my first e30, possibly for sale)
99 Suburban
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Re: Rebuilding an m20b25. Got questions.

Postby M20_fever » Thu Oct 30, 2014 11:26 pm

I looked into it when I was building my stroker, I think its discussed in my engine thread on tech. Bottom line is the material and bore is correct but they would require custom length connecting rods, and even then they are for a 4 valve motor so the dome design is shit when used with the 2v heads we have. Squish, quench, and combustion area are crap. When you factor in the cost of the rods you might as well get custom pistons that work way better, which is what I did.
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Re: Rebuilding an m20b25. Got questions.

Postby 87e30 » Thu Oct 30, 2014 11:40 pm

That's exactly the kind of answer I was looking for. How much were your pistons? Where did you get them?
Schwarz 5-speed 87 325is (newest project)
Arktisblau 5-speed 86 325e (current DD)
Schwarz 5-speed 87 325e (parts car/LS1 swap?)
Gazellenbeige automatic 85 318i (70,000 miles)
Alpine white 5-speed 87 325is (my first e30, possibly for sale)
99 Suburban
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Re: Rebuilding an m20b25. Got questions.

Postby M20_fever » Fri Oct 31, 2014 4:03 pm

I got mine from BRC for ~$800 IIRC. I had them custom designed to match the stock 8.8:1 CR and 885 dome design with improved ring lands, and wrist pin height for 135mm rods and 2.7L crank.
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