The Road to Drag Week 2016 - July 3, 2016

[57 lima bean]

Limabean, "If I remember right, the high-riser motor in the Mach I is fine. It was the transe and rear end that broke, and I think they are both fixed"......They IS.The Mach 1 needs a look see.

[Barry_R]

Yeah - you'd see shiny spots on the gap.  I did a blown engine several years ago and it showed up pretty bad - needed to touch hone, open up gaps, and re-ring that one.  I don't see signs of detonation on the piston - usually it will nibble away at the sharp edges and corners, like the outside diameter and gas ports - those look clean.

Can you take pics of the rings from the sides?  Might be a clue there - maybe.

I was initially thinking that the ring issue contributed to the skirt, but maybe it's "chicken and egg" and the skirt was the initial failure.  Scuffed material might have dragged the ring around.?.?.   What can you provide regarding wall clearances, vacuum, distance from pin centerline to top of piston (Cammer engines require a lot of crevice volume above the top ring, which would intuitively make for a lot of potential rock in the piston.  How much clearance is between the wall and the above the top ring area?  A couple years ago I saw a Mahle design that intentionally used the upper area as added skirt/wall contact surface - something that nobody I was aware of ever did.  Maybe a case could be made for a longer skirt on the thrust side along with more clearance.

Thinking & typing out loud....

[jayb]

I suppose its possible that the skirt was the initial failure, but the scuffing only shows up on three pistons, and all 8 of them show evidence of the support rail moving into the lower ring land; minimum was about 1/4" in, and max was 1/3 of the way around the piston. 

Last night I took the one piston I have left here (the rest are now at the machine shop), and re-assembled the oil ring support rail and oil rings after I had filed down the burrs in the lower ring land and also cleaned up the area by the pin so that the dimple in the support rail is pushing against a vertical wall instead of a thin, tapered spot.  I pushed on the dimple in the support rail with a screwdriver, trying to get it to move into the ring land, and it wouldn't budge.  This leaves me hopeful that this little fix will solve the problem, but I think I'm going to have to re-assemble the engine, run it, and then tear it down again before I know for sure...

[TomP]

An old set of JE pistons I've got use aluminum plugs to retain the pin and have the ring grooves cut in them. They are a 1.13" compression distance so the rings have to overlap the pins. Seems like a way to eliminate snap rings or Spirolox as well.

[Heo]

Aluminium buttons to retain the piston pin is used on aero
engines

[427Fastback]

At one of the shops I worked at we had two flat bottom drag boats.One was a 500+ aluminum KB (blown alky)It used Teflon buttons on the wrist pins...

[Qikbbstang]

Just a general question with all the welding of the ports required on the heads I was under the impression that the "spec" on aluminum and heads was derived via a careful heating & cooling process. Supposedly welding on heads and alum can knock that hardness out making them 'soft' ... when alum heads are substantially welded do mortals get them re-heat treated?..............

[jayb]

I've never had to do that, but then the welding is in the ports, not around threaded areas where hardness is more critical.

[Cyclone Joe]

BB,
The aluminum heads are not heat treated but left in the 'as fabricated', meaning there isn't any post cast heat treatment for strengthening purposes.  Welding isnt going to cost you any strength, as you're in the lowest strength/stress condition in the as-fabricated state.  Now, by operating the engine, you end up heat treating part of the head over time to a T5 or T51 temper, as you only need 300-400F to start that process.  It can start with an even lower temp, say 225-250F, which more of the head could see.

Here's a good article for reference purposes http://www.afsinc.org/files/images/aluminum.pdf

Joe

[jayb]

I don't think that's correct, Joe.  My intake adapters are solution heat treated to T6, and I'm pretty sure that cylinder heads have to go through the same treatment.  One reason is machining; if you don't heat treat the aluminum casting, you end up tearing the metal much more easily when machining the parts, and I think it would be very difficult to get that smooth finish you see on the decks of aluminum cylinder heads. 

I know for a fact that some SOHC heads are heat treated after casting, and I assume all other aluminum aftermarket heads are done the same way - Jay

[Cyclone Joe]

Jay,
Did the casting house share why they go up to a T6 temper rather than leaving it "F"?  Was it to stabilize the casting during machining?  Based on the thermal cycles the part will see on the operating engine, its going to re-temper it down to a T5 anyways, so I'm more curious than anything why they go up to T6.  If it were bar stock I'd get it; clearly I need to study more on cast aluminum 

I wonder how much machine-ability difference there would be, we're talking 6-7% elongation in "F" to 3-4% in the T6 condition.  I could see the argument if the "F" condition was 20% as it would be 'mushy' rather than want to form a chip.  Again, more learning on my behalf needed. 

Learned something new today either way, thanks Jay!

Joe 

[Joe-JDC]

TFS, Edelbrock, Ford all had warnings on cutting too much off the fire deck when their aluminum heads were first brought to the public for use.  Edelbrock used to say that anything over .050" would require sending them back for heat treatment for them to stay flat and not blow head gaskets, or lose their valve jobs.  Many of the small block Ford heads would only get a few races before the valves would no longer seal properly.  The reason was cutting too much off the entire surface weakened the head.   Heat treating is not usually needed where welding is done.  I just repaired a combustion chamber this week for my old shop where they welded the combustion chamber almost entirely up, and cut the chamber to install new valve seats and welded the guide hole before cutting and installing a new guide.  When I finished, it looked like the original CNC combustion chambers of the other three cylinders.  Anyway, if you have an aluminum head and it has been welded on, or cut the deck excessively, you may find the valve job will not seal for long.  If that happens, then it could need a heat treatment issue.  Joe-JDC

[jayb]

Jay,
Did the casting house share why they go up to a T6 temper rather than leaving it "F"?  Was it to stabilize the casting during machining?  Based on the thermal cycles the part will see on the operating engine, its going to re-temper it down to a T5 anyways, so I'm more curious than anything why they go up to T6.  If it were bar stock I'd get it; clearly I need to study more on cast aluminum 

With all three of the casting companies I've worked with, T6 seems to be pretty standard for any casting over about 10 pounds.  The first thing they say is T6 improves machinability, and they also recommend some ageing of the casting, again for machinability.  They also mention thread integrity; if you are going to put threads in the casting, T6 will make them hold more torque.  In addition, with a cylinder head where you are torquing them with bolts or studs to 100 foot pounds or so, a soft casting will compress and you won't get a good torque on the bolts without warping the heads somewhat. 

[Barry_R]

I'm probably gonna goof this up since I am going by memory.  I recall a conversation with our lead engineer at the Malden, MO cast piston plant regarding heat treatment decisions on cast (hypereutectic) pistons.  That facility ran tens of thousands of pistons per day at one point, so they knew something about that stuff. 

He stated that on their castings (obviously much less than 10 pounds each) a T6 treatment would initially test better but would degrade over time and use.  He indicated that the T5 process would initially not test as well but would actually get better over usage and could actually exceed the T6 after accumulated run time.  I'll let those more knowledgable about the processes tell us if he was correct or just trying to get me to be quiet and go away....