Dropped off my block to get re-honed for some new rings and the machine shop calls and tells me I have two cylinders that do not look good and can I come in. When I took it apart (wish I had pics of the cylinders) I saw with my horrible eyes two looked kinda bad and was only scuffed on the sides. So the #6 and #4 cylinders need at least twenty thousands to clean up the out of round. The bores are out of round next to each cylinder and #6 has it on both sides and #4 has it on the #6 side. I brought in my pistons and the #4 and #6 were both just over a thousandth smaller than the other pistons even with the line to line coating. This motor only has around 20 hours and is a bowtie block bored at 4.530 currently but going to 4.560. Pistons are Icon forged. When it was assembled the bores looked perfect. I had it apart due to blowby issues and found some bad leak down numbers. This could be one reason. Any ideas on what could of happened.

Whats your rod stroke and compression height? Engine speed and hours?

Got a call from machine shop and it looks like when the block was machined for these piston it was bored to 4.535 which is way too much for the piston and skirt coating I had. This could of been why I had blow by issues? The engine is a 4.25 stroke, 4.385 rod motor, from what see online the compression height on these are 1.270. Probably about 20 hours and did run it quite a few times on length (around 20-30 minutes) at 4500-5000. Icon piston is local to me and have a friend who does all the race stuff there so he got me a new set of forgedpistons again and is talking to my machine shop which happens to be his. So I am sure it will get done right this time.

I think you mean 6.385 rod..................

That’s a very odd size to accidentally bore to. Your engine builder and machine shop both screwed up. If they aren’t making it right find new ones.

It is at a new one now.

so number 4 and 6 were bored different than the rest.

The blocks bore was/is actually measured at 4.530, and what was the pistons measurement? Was this coating applied from ICON or was it done somewhere else? Im curious what the actual piston to wall clearance was. Any chance the original machine shop bored the extra .005 from the cylinder, due to the coating/piston measurement?

Guess what Im asking is, was piston clearance on target, or , did you simply get the pistons hot and scuff the bores up from a bad tune up

just wanna make sure I'm get this correct. The out of round your refeering to on 4 and 6 is from the scuffs on the sides of the walls correct. Also what was original piston to well clearance .005? Icons site recommends like .007 plus for their 2618 piston but would imagine the exact clearance came with pitons. They do have a FHR the was partially forged that I believe they did away with though. Curious what your new builder is claiming for correct clearance. Wish you coulda got some pics. Seems like you have iron heads and 10.5:1 compression however higher altitude if I remember right and had some reversion issues. You ever replace cam with less overlap? Just going by memory but seems like it was around 24-26 deg. Hope the best for you cause I know you have a lot of time invested and now getting pricier.

Clarification, all bores were bored to 4.535 which is odd but the two pistons in the #4 and #6 holes measured over a thousandth smaller that the other 6. The coating was put on by Icon and is the Line2Line coating and these were not the FHR series but the premium forged. I do not know the exact piston to wall clearance but it seems to be a bit much as hardly any pistons had any coating that was abraded. I will call the machine shop today and get more information on the old and new clearances. It is my understanding that the coated pistons are supposed to be installed tight in order for the coating to abrade into the cylinder wall.

In regards to the tune up I know I was pretty fat for a few trips until I got it leaned out finally.

I am probably putting a set of brodix bb2 on now and getting a new cam ground for the new heads. Should still be around 10:1 but will be a 555 now.