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2012 Mack CXU613 415-C MP8


Dan107
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Quick question about piston design.

The truck dropped an exhaust valve and cracked a cylinder.  I couldn’t afford a Mack cylinder kit, so I purchased an aftermarket one.  Not mentioning the brand, but on the original piston there are two small reliefs molded in alignment with the exhaust valves.  The new piston is flat with no reliefs.  Every other dimension on the new piston is the same.  My question is will it work, or will the exhaust valves strike the new piston?   

511A7DCA-B55E-4DA3-A8C8-D93662054E8B.jpeg

A851E6F2-0220-4A86-9A16-F0F481F96E7B.jpeg

Edited by Dan107
Forgot engine
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Myself, I can't say I had good luck with a mismatched piston. Only did that once in a Detroit Diesel with a customer supplied piston and sleeve assembly but the engine always ran less than 100% when put back together. Not really a miss and compression pressure was very close to the other seven cylinders, (analog gauge) but there was always a slight "stumble" in that cylinder I felt. I'm thinking the brand on the piston and liner was "Speed Pro", but that was many years ago.

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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19 minutes ago, davehummell said:

You could have relief's cut on a mill and then weighed other wise you would have to figure out how far the valves open down in the chamber. This is standard stuff when you're building a racing engine. 

Remember the old modeling clay trick and playing with head gasket compressed thickness(s) to keep the valves and pistons from "Kissing" each other?

Dog.jpg.487f03da076af0150d2376dbd16843ed.jpgPlodding along with no job nor practical application for my existence, but still trying to fix what's broke.

 

 

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9 hours ago, Dan107 said:

Quick question about piston design.

The truck dropped an exhaust valve and cracked a cylinder.  I couldn’t afford a Mack cylinder kit, so I purchased an aftermarket one.  Not mentioning the brand, but on the original piston there are two small reliefs molded in alignment with the exhaust valves.  The new piston is flat with no reliefs.  Every other dimension on the new piston is the same.  My question is will it work, or will the exhaust valves strike the new piston?   

511A7DCA-B55E-4DA3-A8C8-D93662054E8B.jpeg

A851E6F2-0220-4A86-9A16-F0F481F96E7B.jpeg

Not Worth taking a chance on in my mind! don't care how much you saved!Money better spent buying the proper part! The reliefs are there for a reason!

Edited by fjh
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I was restoring a velocette Truxton and I bought a new head it was semi finished valve holes and a ruff hole for the valve guide and chamber was not finished I had at least 30 hours in that head and setting up squish band for the right compression and I had to machine the piston crown for the  hemi head. That is the last British bike I wanted to own.  

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