Piston Clearance

[JDC]

I'm pulling a motor apart to do a rebuild. What is the clearance to just re ring before you need to get an overbore done? I would like to just do rings, bearings and gaskets if that is all that is needed.

[DEEPNHOCK]

Everybody would like to just put rings and bearings in...
Some do..
But you need to check your bores for taper, for roundness, and for wear.
Pistons need to be measured and compared to the bore.
Ring lands need cleaning and measuring, too.
You didn't say which engine, or year, so you can't get good info back.
The Stude shop manual has all your numbers in the Group III section.

To answer your initial question....
According to the shop manual...(on a V8)
Cylinder bores should be reconditioned if they are scored, out of round, or tapered in excess of .005".
(Section III, page 35)

You'll get a lot of feedback, as preferences vary.
But it's your engine, and how long it will last is dependent on your work.
Good luck with your rebuild.
Don't be askeered of it!
Jeff[8D]

quote:Originally posted by JDC

I'm pulling a motor apart to do a rebuild. What is the clearance to just re ring before you need to get an overbore done? I would like to just do rings, bearings and gaskets if that is all that is needed.

[Mike Van Veghten]

As Jeff says, many ways to acomplish the same thing...

But to me, if you are going to take the time to pull the engine down for "some quicky work"..., spend the time, do it right.
Save another paycheck and buy pistons, bore the block, install the rings correctly, etc., etc.

Your engine and the driver will be much happier in the end..

Mike

[PackardV8]

quote:What is the clearance to just re ring before you need to get an overbore done?

1. Buy a Shop Manual and read it carefully. It is the first part one needs to have to re-build a Stude engine. "Cylinder bores should be reconditioned if they are tapered in excess of .005"

2. Someone who knows how with a dial bore gauge or inside micrometer should verify cylinder wear and with an outside micrometer, piston skirt collapse. Back when money was tight and labor was cheap, many a Stude engine was re-ringed without checking anything. However, even for CASOs, if the difference between the bore diameter at the top of the bore wear ring and the piston skirt is greater than .010", it is a waste of time and money to re-ring.

thnx, jack vines



PackardV8

[JDC]

I actually have one on a stand in the garage. I just got a set of calipers, micrometers, all that stuff and was going to try to learn how to measure everything. I figured if I didn't need to overbore, I wouldn't, I just couldn't find the number. Thanks boys.

[hotrodstude]

it's an old school cheap fix but "kneeling" of the pistons is one way to fix the clearance problem. using a kneeling tool you run the tool over the skirts of the pistons raising the metal to decrease clearance between the piston and the cylinder walls. i ve used this method several time but only on low proformance engines.like cheevy straight six's. it added about 100,000 miles of engine life on the old stovebolt.see second post

2006,f-150,2x4,v-6,5-speed manual,8ft bed, will post stude info when i get it on the road.

[PackardV8]

quote: "kneeling" of the pistons

Am long-familiar with machine-knurling pistons to raise a cross-hatch pattern and make up for wear on piston skirts. Also, have used a manual tool from Sealed Power which has a flat wheel and a narrower curved wheel which can somewhat restore collapsed skirts.

However, the term "kneeling" is unknown to me and a search did not turn up an info. Can you describe in more detail what it does and how it works.

thnx, jack vines

PackardV8

[allstateguy]

I think he meant "knurling"
Back in the dark ages, it was done to the ID of valve guides and about a 2 square inch "pad" on each side of the piston skirts to take up some of the slop.
Knurling tools would even emboss the tool manufacturer's name on the piston skirt.
Looks cool, very arguable as to value.

JohnP, driving & reviving
an early Lark

[Dan Timberlake]

An estimate of cylinder taper can be done by checking a compression ring's end gap near the top off the cylinder (below the ridge) and near the bottom of the cylinder. Taper is approximately the change in the gap / 3.14.

[hotrodstude]

quote:Originally posted by hotrodstude

it's an old school cheap fix but "kneeling" of the pistons is one way to fix the clearance problem. using a kneeling tool you run the tool over the skirts of the pistons raising the metal to decrease clearance between the piston and the cylinder walls. i ve used this method several time but only on low proformance engines.like cheevy straight six's. it added about 100,000 miles of engine life on the old stovebolt. spelling is not my strong suit.plus i'm on medication which some times effects my mental state but your right packardv-8.i only used it on cheap rebuilds and you can't get much cheaper than a cheevy. but i dose work.

2006,f-150,2x4,v-6,5-speed manual,8ft bed, will post stude info when i get it on the road.

2006,f-150,2x4,v-6,5-speed manual,8ft bed, will post stude info when i get it on the road.

[buddymander]

I wouldn't worry too much about bore wear. The ridge will tell the story. The real question is how the engine operated before you took it apart. Good info to have if you are looking to just overhaul. You can do a great knurl job on the pistons with a pick hammer. Just back up the skirt real good with some hardwood and pick it about every quarter inch. Then run a file over it to knock down the high spots so it will barely go into the cylinder with a slight drag. Keep the file parallel to the bore; never turn it sideways. The real issue on a cheap overhaul is maintaining good oil pressure, where no chances should be taken. If you have any doubts about the crank, then take it in and have it checked. Cam bearings can cause low oil pressure, so you might want to have them checked. They're cheap, and they probably have never been changed. Make sure that the rod throws have near perfect clearance; the mains aren't as important. Take the oil pump apart and check it for visible wear. Put it back together and re-use it if it looks okay. Valve seals are important to keep a motor from smoking and burning oil. You should at least lap your valves and make sure that the umbrella seals are all intact. Be sure to check your valves by mounting the head so that the valve faces are straight up and then pour thin oil in the chamber enough to fill the edges of the valves and shoot compressed air in the ports. Any bubbles at all is not acceptable.

[Dan Timberlake]

Any ridge needs to be removed, and the transition to the old ring travel surface must be near perfect, as the new top rings may bump into it. The crafty British used to sell "ridge dodger" rings (with a notch in the top ring's upper corner) so the common bloke could re-ring his Morris every few years at home without fancy tools.

[Chucks Stude]

One thing that I have noticed on these older engines, is an increase in clearance between the wrist pin, and the piston. If there is excessive clearance, and you rebuild the engine without addressing this, you get an engine that has a deep knock. I usually check them by trying to rock the piston over the wrist pin, and see if there is any play. CASO way of doing it, but beats nothing.