7M Cylinder Chamfer

HeWhoOvercomes

HeWhoOvercomes

Vrooom VROOOM
Apr 23, 2011
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The Corner of Happy & Healthy
Hey guys! My machinist asked me if I want him to chamfer (bevel) the edges of the cylinder...he says he does it on almost all the blocks they machine and that it helps make assembly easier. He then showed me a BMW Z4 block making around 1000 hp that the customer requested that they leave sharp because of the relatively thin cylinder walls. What does everyone recommend when machining a 7M block?

Thanks!
 
atmperformance

atmperformance

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Sep 17, 2013
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San jose
Suprapowaz!(2);1978563 said:
Why not?
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less sealing surface area. removing a burr if fine but i wouldn't machine metal away from a matting surface. you're just setting yourself up for leaking coolant and a BHG
 
atmperformance

atmperformance

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Sep 17, 2013
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San jose
it's not hard to get the rings in with a square edge. also your piston sticks up out of the block on the 7m if you Chamfer too much or have a block that's been resurfaced a lot you could see issues with your top ring but that's a bit of an extreme case.
 
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IJ.

Grumpy Old Man
Mar 30, 2005
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One thing you need to keep in mind is if you don't deburr the tops of the bores (and every other hole and sharp edge in the block after machine work) is you run the risk of a stress riser turning into a crack...
 
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terrenceLP

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Mar 22, 2011
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Update - go to post #11

Keep in mind this is a 7m, so ANYTHING around the headgasket area should be following the TSRM rebuild process. And like anything else, first time will challenge you. I would let your machinest put the block back together for a number of reasons if you have never done it and it's your only motor. Main reason is ring gaps, that can take time ND be a pain without the proper tools. Now getting it Blueprinted is another thing, on a old 7m, it's not a bad idea while it's in the shop.
 
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IndigoMKII

IndigoMKII

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May 9, 2011
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terrenceLP;1978982 said:
Keep in mind this is a engine, so ANYTHING around the headgasket area should be following the TSRM rebuild process. And like anything else, first time will challenge you. I would let your machinist put the block back together for a number of reasons if you have never done it and it's your only motor. Main reason is ring gaps, that can take time AND be a pain without the proper tools. Now getting it Blueprinted is another thing, it's not a bad idea while it's in the shop.
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Fixed this for you. Certain steps should be taken regardless of whether its a 50's flat head or a brand new LSX. Most of the shitty 7m claims come from people who take short cuts or are too cheap to buy what they need the first time so I wouldn't find it to be a fair claim to do all this because it's an 'old 7m'.

Also, ring gaps aren't the only concern with building an engine. You need to decide before the engine is built as to what you're going to do with it. Do you want the bearing clearances tight or loose? Is the proper specs being used for the thrust bearings? What about setting the valve shim clearance on the head? Kick a bucket out when you're just now breaking in a brand new engine and you might not be very happy.
 
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