Blown Yellow

Hello,

I have a lunati 409 in my 2001 silverado and had to tear it down after 12,000 miles because of what sounded like a rod bearing. Once I got the pistons out I found that the number five piston skirt was extremely worn and grooved, aswell as the bore. The ring lands and top of the piston are as they should be and now I am racking my brain trying to figure out what went wrong.

I have yet to mic the bore to make sure that the builder did it to spec but was curious if anyone has any suggestions as to the cause?

Thanks,

Martin

GueSS Who

What is your bore and stroke on that one.

Magic Chicken

iTrader: (1)

408 is 4" stroke 4.030" bore

BOWTIE

Could be any number of things... debris in the cylinder, if it has moly rings a piece of it could have broken off, could have a burr at the bottom of the cylinder both wiping oil off the skirt and scraping the skirt, bore could have been set up too tight, motor could have been run too hot, there are a ton of things that could have caused it. Hopefully you get it figured out and fixed.

Green Thunder

iTrader: (11)

Any chance of posting a pic?

Blown Yellow

I will get a picture posted on Monday, I was starting to lean towards the cause being debris but I can't find any broken rings or anything obvious. I will grab a good mic set from my pops shop and check for bore taper and size on Monday as well.

Green Thunder

iTrader: (11)

Cool, look forward to seeing the pics!

racer7088

Could be deris from the valvetrain since after initial startup as you will have a lot of this wearing off in the first few miles. What's important is what is up in the tops of the cylinders. Also the bottom of the bores need to be chamfered after honing but few shops do this. You're probably fine.

On an all out race engine sometimes we will deburr and chamfer every single spring and this cuts down on these debris a lot but it is incredibly labor intensive. This would be on say a NASCAR or 25K and up kind of engine where you are getting payed to do this sort of thing. No one works for free and you can easily put 20 hours of just prep like this into some of these deals.

Of course without seeing it there is no real way to tell as the next biggest cause of this is simply dirty engine assembly. You'd have to see if the bearings are also also all scored up. If they are then you might have a case of probably an engine not put together too clean but if they are perfect it's probably more like what I wrote about above.

BOWTIE

[QUOTE=racer7088]Could be deris from the valvetrain since after initial startup as you will have a lot of this wearing off in the first few miles. What's important is what is up in the tops of the cylinders. Also the bottom of the bores need to be chamfered after honing but few shops do this. You're probably fine.

I used to chamfer them after the bore job but before the hone... and I always like to finish the cylinders with a brush as well, which would remove or roll over anything that might have been left after the hone.