checking piston rings?

[shaun89]

to make a long story short,my truck was mis-firing,i couldnt fix it easily,so i did a compression test. everything was good (170psi) except #6,it went to 50psi..so i took off my heads today and my exhaust valve spring on #6 is snapped. but i still want to check my rings to make sure before i move to rebuilding the heads. its a crate motor with only 25k on it (ya i no) but my question is, is there anyway to check if the rings r good with the bottom end in and heads off?

 

[Fordum]

Someone with more experience than me may jump in with a way, but I don't know of one that is reliable.
You could try to work a feeler gauge between the piston and the cylinder wall, but all that would tell you is cylinder wear.
When setting things up, sometimes you do that and measure how hard it is to pull a certain thickness gauge out, but I don't think its applicable here.

This is about a good a test as any.
Stick your finger in a cylinder about a half inch. Press the edge of your fingernail into the wall like you are trying to scrape off a coating.
Slide the finger up and out. Right at the top is a thin section of cylinder wall that the rings never touch.
So it is the original thickness.
In a worn engine, you get quite a "ridge" there. The thickness of that ridge is how much wear you have. Which should be equally divided between the rings and wall.

On a well worn engine, it can be quite thick. I would not expect for you to be able to feel more than a slight rough spot.

Also, look at the top of the pistons. Since its a rebuilt, you may have oversized pistons. If so, they probably have the size stamped in the top.
They should all be the same.

I once got a factory rebuilt short block that had 7 standard pistons and one .060 over.
I sent it back.

 

[ryoken]

if there's no signs of vertical scoring in that cylinder, they should be fine.... you have no reason to suspect otherwise, you found the issue... as long as the cylinders look even among all 8, proper valve seating should bring that cylinder up to the others... doubtful you'd have a ridge with that mileage, heck ya might still have some x-hatch....

 

[4X4HIGH]

Rings will rarely give you low compression unless they are completely broken. Your issue is that broken valve spring. Don't just replace the spring, make sure that valve gets checked to make sure it didn't hit the piston and get bent. Then you also need to question WHY the spring broke in the first place.

 

[shaun89]

awesome,thanks for all the help guys! and ya,im afraid of why it broke in the first place,my friends say i drive like a grandma,so im hoping it was a freak accident. and another thing,i snapped off literally half of the rocker studs half way through the rocker nut. screw that company, im building my next engine...but back to the issue. it does have decent lift. its .525 with 1.6 rockers so i think thats about .560 lift. but the heads are built to handle it. they are vortec performance. so the only thing i can think of that would cause it to break is maybe the amount they are moving.

 

[4X4HIGH]

awesome,thanks for all the help guys! and ya,im afraid of why it broke in the first place,my friends say i drive like a grandma,so im hoping it was a freak accident. and another thing,i snapped off literally half of the rocker studs half way through the rocker nut. screw that company, im building my next engine...but back to the issue. it does have decent lift. its .525 with 1.6 rockers so i think thats about .560 lift. but the heads are built to handle it. they are vortec performance. so the only thing i can think of that would cause it to break is maybe the amount they are moving.

If the cam card says ".525" with 1.6 rockers" then that's what it is.

Unless someone took the heads apart and machined them to accept that much lift there is your problem. Vortec heads factory can only accept about .460" lift before the retainers bottom out against the seals/guide which at that point will either break valve springs, break rocker studs, or snap a valve in half at the keeper groove.

 

[shaun89]

If the cam card says ".525" with 1.6 rockers" then that's what it is.

Unless someone took the heads apart and machined them to accept that much lift there is your problem. Vortec heads factory can only accept about .460" lift before the retainers bottom out against the seals/guide which at that point will either break valve springs, break rocker studs, or snap a valve in half at the keeper groove.

o ok,i thought the 1.6 compared to 1.5 added a tiny bit more lift.but ive heard my heads arent stock vortecs,they are aftermarket vortec style that can accept that much lift. i will check to make sure though,thanks

 

[shaun89]

i should really update my membership....but anywho...i need to find springs for my heads,and i am not sure what to get. im guessing they would be a little stiffer than oem because of the amount of lift i have. they are a single spring...i could measure the ID and OD but i dont have any gauge to measure how stiff they are. any suggestions on how to go about this?

 

[4X4HIGH]

i should really update my membership....but anywho...i need to find springs for my heads,and i am not sure what to get. im guessing they would be a little stiffer than oem because of the amount of lift i have. they are a single spring...i could measure the ID and OD but i dont have any gauge to measure how stiff they are. any suggestions on how to go about this?

You need the specs for the cam in order to purchase the correct springs. You will also need to know what the installed height is on the heads you have (distance between the spring pocket and the underside of the retainer). Without BOTH of these pieces of info you cannot even come close to getting the correct springs.

 

[shaun89]

You need the specs for the cam in order to purchase the correct springs. You will also need to know what the installed height is on the heads you have (distance between the spring pocket and the underside of the retainer). Without BOTH of these pieces of info you cannot even come close to getting the correct springs.

ok thanks,i no my cam specs,but the installed height i will have to check.....to the hunt!