Scratched cylinder walls pt 3: final thoughts?

Scratched cylinder walls pt 3: final thoughts?

Joined: July 23rd, 2002, 1:02 am

September 9th, 2011, 12:03 pm #1

Any final thoughts, guys, before I take it up the engine builder? Finally got around to pulling out a piston (#6) from the 408 and did some measuring.

1) measured the bore - consistent throughout (4.03"). Looked like it was bored to spec
2) measured the piston skirt (4.029")
3) measured rings in bore (.022") with no burring or sharp edges

My mechanical engineering/Pontiac gearhead buddy helped me check things out. His final thoughts:
* Engine looks to have been machined well / assembled well other than the engine builder's error of the failed head dowel which caused all the engine smoke and some of the final honing
* the scuffing in the cylinder walls is due to the short pistons and due to the extreme stroke. He originally thought the builder may have set the engine up too loose but somewhat changed his mind once we measured the cylinder/piston/ring gap
* thinks the one large vertical scratch is from something getting lodged in the cylinder. and as it's a vertical scratch, I'll have no problems. You may remember in an earlier thread I did a leakdown test and all cylinders were holding above 95%
* thinks the motor would "live" and run fine

Here is the backstorhttp://www.network54.com/Forum/119419/t ... +%28pix%29

Final photos:
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]

Last edited by 71Rcode on September 9th, 2011, 12:07 pm, edited 1 time in total.
Quote
Like
Share

Joined: May 20th, 2005, 4:48 pm

September 9th, 2011, 12:57 pm #2

....like the ones in the bottom picture are normal. The big, long scratch that you're showing a picture of is not normal. Make sure that the rings are ok on that piston. Also check the end gap of the top rings and make sure that they don't have a huge burr from where they were filed.

How deep is the scratch?

As far as measuring, where did you measure the pistons? .001" of piston/wall clearance is not enough, even for cast pistons. Most pistons are to be measured 90° to the wrist pin, about 1/2" up from the bottom of the skirt. Dial calipers will not give you an accurate estimate for either the bore or the piston. Forged pistons need to be ran at anywhere from .0035-.006 depending on the manufacturer. Most of them are in the .004-.005" range.

Brent Lykins
B2 Motorsports, LLC






Quote
Like
Share

Joined: February 28th, 2008, 4:15 pm

September 9th, 2011, 1:03 pm #3

Any final thoughts, guys, before I take it up the engine builder? Finally got around to pulling out a piston (#6) from the 408 and did some measuring.

1) measured the bore - consistent throughout (4.03"). Looked like it was bored to spec
2) measured the piston skirt (4.029")
3) measured rings in bore (.022") with no burring or sharp edges

My mechanical engineering/Pontiac gearhead buddy helped me check things out. His final thoughts:
* Engine looks to have been machined well / assembled well other than the engine builder's error of the failed head dowel which caused all the engine smoke and some of the final honing
* the scuffing in the cylinder walls is due to the short pistons and due to the extreme stroke. He originally thought the builder may have set the engine up too loose but somewhat changed his mind once we measured the cylinder/piston/ring gap
* thinks the one large vertical scratch is from something getting lodged in the cylinder. and as it's a vertical scratch, I'll have no problems. You may remember in an earlier thread I did a leakdown test and all cylinders were holding above 95%
* thinks the motor would "live" and run fine

Here is the backstorhttp://www.network54.com/Forum/119419/t ... +%28pix%29

Final photos:
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
Everything looks pretty good, but I would double check the piston size to bore size. Your measured clearance of .001 is too tight for that piston. Did you measure the bore with an inside mic and then measure the inside mic with the same outside mic you used to measure the piston? The scratches from the skirts are normal but the big scratch is a little odd as it goes from above the top ring land to well down on the skirt. I would check the piston to wall clearance and then give her a good cleaning and put the short block back together. I would also take the heads apart and check for a bad valve guide.
Andy
Quote
Like
Share

Joined: December 16th, 2003, 11:56 pm

September 9th, 2011, 1:35 pm #4

Any final thoughts, guys, before I take it up the engine builder? Finally got around to pulling out a piston (#6) from the 408 and did some measuring.

1) measured the bore - consistent throughout (4.03"). Looked like it was bored to spec
2) measured the piston skirt (4.029")
3) measured rings in bore (.022") with no burring or sharp edges

My mechanical engineering/Pontiac gearhead buddy helped me check things out. His final thoughts:
* Engine looks to have been machined well / assembled well other than the engine builder's error of the failed head dowel which caused all the engine smoke and some of the final honing
* the scuffing in the cylinder walls is due to the short pistons and due to the extreme stroke. He originally thought the builder may have set the engine up too loose but somewhat changed his mind once we measured the cylinder/piston/ring gap
* thinks the one large vertical scratch is from something getting lodged in the cylinder. and as it's a vertical scratch, I'll have no problems. You may remember in an earlier thread I did a leakdown test and all cylinders were holding above 95%
* thinks the motor would "live" and run fine

Here is the backstorhttp://www.network54.com/Forum/119419/t ... +%28pix%29

Final photos:
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
If not an immediate oil control issue it could lead to an issue with a snagged ring or split cylinder wall down the road.
Quote
Like
Share

Joined: January 10th, 2002, 5:53 pm

September 9th, 2011, 2:00 pm #5

Any final thoughts, guys, before I take it up the engine builder? Finally got around to pulling out a piston (#6) from the 408 and did some measuring.

1) measured the bore - consistent throughout (4.03"). Looked like it was bored to spec
2) measured the piston skirt (4.029")
3) measured rings in bore (.022") with no burring or sharp edges

My mechanical engineering/Pontiac gearhead buddy helped me check things out. His final thoughts:
* Engine looks to have been machined well / assembled well other than the engine builder's error of the failed head dowel which caused all the engine smoke and some of the final honing
* the scuffing in the cylinder walls is due to the short pistons and due to the extreme stroke. He originally thought the builder may have set the engine up too loose but somewhat changed his mind once we measured the cylinder/piston/ring gap
* thinks the one large vertical scratch is from something getting lodged in the cylinder. and as it's a vertical scratch, I'll have no problems. You may remember in an earlier thread I did a leakdown test and all cylinders were holding above 95%
* thinks the motor would "live" and run fine

Here is the backstorhttp://www.network54.com/Forum/119419/t ... +%28pix%29

Final photos:
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
Like the others - everything looks normal except your .001 wall clearance and the one scratch. I'd suspect some sort of debris that made the scratch. It may or may not still be there, and could have just as easily come in from the intake.

Double check your piston measure - you should see something more in the 4.026 or .027 range for the skirt. My Probes ran about 4.0255 and the old TRWs ran 4.0275

1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.
Last edited by Falcon67 on September 9th, 2011, 2:01 pm, edited 1 time in total.
Quote
Like
Share

Joined: February 3rd, 2003, 5:22 pm

September 9th, 2011, 2:03 pm #6

If not an immediate oil control issue it could lead to an issue with a snagged ring or split cylinder wall down the road.
take a close look at the pic showing the ring installed near the top of the bore. It appears (unless the camera angle lies) that the ring ends weren't filed square but actually have a taper. Put another way, the gap clearance is greater on the inside (facing the ring land) than on the cylinder wall side. Easy to measure with a set of feeler gauges if this is true. Aside from some potential but minor ring butting (major = broken rings!) if no one smoothed off the ring ends with as stone after filing, the large/long scratch happened right from the get-go when the piston was installed. The sharp edged ring scratched the bore from the deck all the way down. This can be the only explanation as to why the scratch starts above the ring's normal path.
Quote
Like
Share

Joined: July 23rd, 2002, 1:02 am

September 9th, 2011, 2:06 pm #7

If not an immediate oil control issue it could lead to an issue with a snagged ring or split cylinder wall down the road.
Thanks, everyone. Bob, so you think a sharp/misfiled ring end caused that big long scratch? And there is no way something could've fallen into the cylinder and gouged it like that? (want to cover my bases before talking to the builder).

We removed the rings on that piston and they were fine. Definitely no burrs on the ring end gaps. That was the first thing I checked. The scratch is not as deep/extreme as it appears. Definitely catches your fingernail though. And I wouldn't think it could catch a ring as the scratch is completely vertical.

Brent and Andy, looking back, our measurements were taken not using the most ideal/precise instruments. Believe we used a snap gauge for the bore and a ruler-style micrometer. Wish we would've had better tools for the job....but we basically wanted to get in the ballpark. My figure on the piston size looks to be incorrect. These are the specs from Probehttp://www.probeindustries.com/ProductD ... =TechSpecs

My initial guess was that the builder bored the block before getting the pistons...thus, the reason behind the pistons rocking slightly in the cold bore = what we thought was a loose assembly.

At a minimum, I'll ask him to disassemble and clean the rotating assembly and then clean up the cylinder walls as needed. Also the heads. Great advice, Andy.
Last edited by 71Rcode on September 9th, 2011, 2:10 pm, edited 1 time in total.
Quote
Like
Share

Joined: February 3rd, 2003, 5:22 pm

September 9th, 2011, 2:57 pm #8

I don't believe anything fell in. And the ring's ends are, of course, now smooth as the sharp edge was worn down in the process of the piston's travel while gouging the softer cylinder wall material.

If you've never tried to file the end gaps on a ring, give it a try on a junk ring with a sharp file....then check the edges of the ring where it would touch the cylinder wall by dragging a silk cloth or some material like that. Any snags = too sharp of an edge and time for some light stone action.

Btw, since it appears your piston-wall clearance is too tight anyway, most of that scratch and the minor ones may all disappear with a hone job.
Last edited by machoneman on September 9th, 2011, 3:04 pm, edited 1 time in total.
Quote
Like
Share

Joined: December 16th, 2003, 1:59 am

September 12th, 2011, 9:43 am #9

Any final thoughts, guys, before I take it up the engine builder? Finally got around to pulling out a piston (#6) from the 408 and did some measuring.

1) measured the bore - consistent throughout (4.03"). Looked like it was bored to spec
2) measured the piston skirt (4.029")
3) measured rings in bore (.022") with no burring or sharp edges

My mechanical engineering/Pontiac gearhead buddy helped me check things out. His final thoughts:
* Engine looks to have been machined well / assembled well other than the engine builder's error of the failed head dowel which caused all the engine smoke and some of the final honing
* the scuffing in the cylinder walls is due to the short pistons and due to the extreme stroke. He originally thought the builder may have set the engine up too loose but somewhat changed his mind once we measured the cylinder/piston/ring gap
* thinks the one large vertical scratch is from something getting lodged in the cylinder. and as it's a vertical scratch, I'll have no problems. You may remember in an earlier thread I did a leakdown test and all cylinders were holding above 95%
* thinks the motor would "live" and run fine

Here is the backstorhttp://www.network54.com/Forum/119419/t ... +%28pix%29

Final photos:
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
it is looking like a need to double check that there was enough clearance for the alloy of those pistons. my builder set the clearances on my new build a little on the loose side, i wanna say about .0065" IIRC for forged pistons on the street

at first i said i didn't see scuffing, maybe that's what it looks like when the oil clearance gets expanded out of existance and the pistons get a little dry?

if your guy set them up as for Hypers.... Oooo

there'll be phantoms, there'll be fires on the road... and the white man dancing
Quote
Like
Share

Joined: November 25th, 2006, 4:54 am

September 12th, 2011, 3:44 pm #10

Any final thoughts, guys, before I take it up the engine builder? Finally got around to pulling out a piston (#6) from the 408 and did some measuring.

1) measured the bore - consistent throughout (4.03"). Looked like it was bored to spec
2) measured the piston skirt (4.029")
3) measured rings in bore (.022") with no burring or sharp edges

My mechanical engineering/Pontiac gearhead buddy helped me check things out. His final thoughts:
* Engine looks to have been machined well / assembled well other than the engine builder's error of the failed head dowel which caused all the engine smoke and some of the final honing
* the scuffing in the cylinder walls is due to the short pistons and due to the extreme stroke. He originally thought the builder may have set the engine up too loose but somewhat changed his mind once we measured the cylinder/piston/ring gap
* thinks the one large vertical scratch is from something getting lodged in the cylinder. and as it's a vertical scratch, I'll have no problems. You may remember in an earlier thread I did a leakdown test and all cylinders were holding above 95%
* thinks the motor would "live" and run fine

Here is the backstorhttp://www.network54.com/Forum/119419/t ... +%28pix%29

Final photos:
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
[/IMG]
Aren't the top and bottom oil support ring/rails supposed to be positioned 180 out from each other for better oil control? I see the gaps on yours are directly in line with eachother. I pulled my motor down recently which was getting oily in one cylinder and all the other 7 pistons had the support rail gaps 180 out from eachother and the oil cylinder had them lined up (making a gap)....allowing more oil in that cylinder???
Quote
Like
Share