351W long rod very short life

[Guest]

[ranchopower]

8 months building up a nice N/A motor for a 93 coupe, made it to the track friday night, first pass 8.90 at 90 mph with a 2.40 short time.
Second pass about 86 mph the K/B 276 piston #4 decided it worked better in the oil pan.
munch munch munch,  conneting rod a lil bent and nice big hole in the #4 cylinder.
No bent pushrods but #4 valves nicely bent.
Nice way to testN tune
Looking at some Mahle pistons now.
Here is the build as we did it, and new carnage pics maybe 2morrow
http://www.ranchopower.com/jims-351w/

Javier

[ranchopower]

Carnage photos finally, and we decided to repair and carry on with the same pistons, so one replacement piston, one sleeve in the block maybe two.
 one each new intake/exhaust valves and a new connecting rod.

http://www.ranchopower.com/wp-content/uploads/2009/12/Picture-0012.jpg

http://www.ranchopower.com/wp-content/uploads/2009/12/Picture-0022.jpg

http://www.ranchopower.com/wp-content/uploads/2009/12/Picture-0042.jpg

http://www.ranchopower.com/wp-content/uploads/2009/12/Picture-009.jpg

http://www.ranchopower.com/wp-content/uploads/2009/12/Picture-0121.jpg

Javier

[69 Merc]

That sucks.  What caused it?

[ranchopower]

Tune out to lunch 

I have not been able to come up with a conclusion as of now. Fact is the piston could not hold the pressure/heat, so my next tune will be colder plugs less total timing and a EGT in the dang car!
I am doing this with my buddy Jim so we try to make the best with a few dollars and a few ideas.
I build it and he helps wrench, but he owns the whole deal.
So far it has been fun even with this flesh wound 

Javier

[grslms51]

wow,that thing shattered..are they hyper-pistons?

[69 Merc]

Tune out to lunch 

I have not been able to come up with a conclusion as of now. Fact is the piston could not hold the pressure/heat, so my next tune will be colder plugs less total timing and a EGT in the dang car!
I am doing this with my buddy Jim so we try to make the best with a few dollars and a few ideas.
I build it and he helps wrench, but he owns the whole deal.
So far it has been fun even with this flesh wound 

Javier

So next time 34* total timing?   

[RunninHorse]

ouch

[ranchopower]

Tune out to lunch 

I have not been able to come up with a conclusion as of now. Fact is the piston could not hold the pressure/heat, so my next tune will be colder plugs less total timing and a EGT in the dang car!
I am doing this with my buddy Jim so we try to make the best with a few dollars and a few ideas.
I build it and he helps wrench, but he owns the whole deal.
So far it has been fun even with this flesh wound 

Javier

So next time 34* total timing?   

That was with 20 intial timing @1000 rpm  and total 32 @ 4000 rpm

Maybe try 25 total next try

Javier

[turbo2256]

What RPM did you shift at.

One ting I wouldnt do is build a hipo motor with any kind of cast pistons. Cheep forged are better than expensive cast.

[injectedrod]

Scary and very hard on the wallet

[ranchopower]

It had a 6800rpm pill that day thankfully.
I tore the rest of the motor down and found every rod bearing spun but no damage,    except for all the tangs ripped out that hold the bearings in the register 
the rod journals and bearing faces are in new condition. 
I will get pics soon.
I Wont be using total seal top ring again, I think that was the straw...

Javier

[turbo2256]

I would be more interested in if the rods big end and or crank were sized properly than blaming it on the piston rings. I have run into the issue of a shop machining some of my stuff before and because they didnt check there micrometers very often the rods big end was off and had to have them redone. I was lucky in that I cought it before assembly.

Not shure what cam or springs in the engine but just one weak spring could have caused the problem.

[ranchopower]

I would be more interested in if the rods big end and or crank were sized properly than blaming it on the piston rings. I have run into the issue of a shop machining some of my stuff before and because they didnt check there micrometers very often the rods big end was off and had to have them redone. I was lucky in that I cought it before assembly.

Not shure what cam or springs in the engine but just one weak spring could have caused the problem.

Well we will redo the same combo now, with JE pistons, rods making a trip for machine,
all the rest of the combo the same, Dart alum  heads 276cfm @.600 low lift very good cfm
combustion chamber 55cc, new pistons now have .100 inverted dome, engine was at 11.5:1 with F/T pistons at .005+ deck.
So a new block, new set of pistons, rings, one connecting rod, a balance and one intake and exhaust valve and we are back in the game if everything else is good, so far so good.

I will check all the springs for any differences, they are K-800 set up at 1.750 I set them at .060 CB clearence, looks as if it was working good, no marks on the pistons and no bent pushrods so we shall see in the near future how it runs again...
Javier

[scienceguy]

Get some quality mics and learn to use them.  Machine work quality varies WILDLY.  Often, there's more bad work out there than good.

For something that is going to be run hard, go toward the looser side of spec to avoid spun bearings.  Many shops just grind the crank down until it's just 'in spec' which leaves the crank on the large side, and the bearings on the tight side.  The looser clearance also tends to leave a little more room for error. 

Piston rings with KB hypereutectics...  These require significantly more gap on the top ring.  The top ring runs hot in these, and without the extra gap, the ring will stick in the bore at TDC, and when the rod pulls it back down, it breaks the ring land off. 

[ranchopower]

Get some quality mics and learn to use them.  Machine work quality varies WILDLY.  Often, there's more bad work out there than good.

For something that is going to be run hard, go toward the looser side of spec to avoid spun bearings.  Many shops just grind the crank down until it's just 'in spec' which leaves the crank on the large side, and the bearings on the tight side.  The looser clearance also tends to leave a little more room for error. 

Piston rings with KB hypereutectics...  These require significantly more gap on the top ring.  The top ring runs hot in these, and without the extra gap, the ring will stick in the bore at TDC, and when the rod pulls it back down, it breaks the ring land off. 

I had gapless top rings, HAD,  the remaining 5 pistons with rings pinched in the grooves, will take the nice rings to the scap pile 

I have never seen 8 spun bearings and no physical damage but soon a trip to the rod machine will tell a story, and I will share results.

Javier