68 327 Piston and ring question

[Happy_dan]

I am refreshing my 1968 C-20 327 4BBL automatic engine. I have it stripped down to block. The crank and heads are at machine shop.

I will be replacing main and rod bearings but hoping to keep the rods and pistons that are in it. They are in good shape and I don't want to buy pistons on top of everything else unless necessary.

I am planning in simply deglazing cylinder walls and hoping to replace rings only. It was using oil and dry and wet compression test revealed a couple of weak cylinders so I think it needs rings.

My question is, can I simply buy standard rings and replace them, or do I need to have cylinders bored and go .30 over?

I measured bores on an x and y axis in center middle and top and they range from 3.976 to 4.003. Most are 3.997 to 4 exactly.

I have searched for information but not sure on what to search for to find the limitations of standard rings and I know we have a lot of expertise here!

[vince1]

Not being a qualified engine builder I can't advise on your numbers but when doing ring and bearing overhauls, if the pistons come out without having to use a ridge reamer then for me its usually OK to do it that way. Then they should be good for another 50k miles.

I've got a couple of 350 blocks that someone gave me over twenty years ago and someday I do plan on going over them and doing the required machine work. With the price of parts so cheap for that engine they could be fun projects.

[Happy_dan]

This is my first engine refresh and I am learning a lot. I really love doing it and even though I am old, life did not allow me to do this type of work so I have very little experience and that is why I have to ask these questions. I have been watching youtube videos and getting advice from friends and here! They are simple engines and are great to learn on.

[vince1]

I did my first overhaul at 13 to a free to me 1951 Thames pick up, all because it didn't run because of a cracked rotor. I never did get the second gear working but after freeing up all the mechanical brake clevises I could get all four wheels to slide.

You're probably watching the same guys as me. Squatch 253 and Watch Wes Work?

[Happy_dan]

I have been watching a wide variety but Pete's Garage has a very good series on a chevy rebuild

[AussieinNC]

327 standard bore is 4.001 inches....

Did you check the piston ring lands on each piston ? Look for wallowed out lands and a build up of carbon behind the ring when its fitted to the piston....
if you can move the ring up and down in the groove its too worn to use....IMHO...

The rings need to be held snuggly by the piston or they will flutter and the engine will use oil....

Clean up the pistons and insert each into its bore and measure the clearance between the piston and the bore...use long feeler gauges...write each measurement down and post the results....

If it was my engine...I look at it this way....you are having the crank and heads done...dont skimp now and leave the pistons as the weakest link...

I always do the following....

Hot tank the block and check for cracks....machine shop job
(make sure they pull the oil gallery plugs so all the crud can come out)
If its cracked anywhere, its junk....
Have the decks checked for flatness and equidistance from crank centerline...
If no cracks, have them bore the block to +030....machine shop job...provide the shop with the pistons and tell them your intended use....
Hypereutectic pistons are a good street choice....
Have the connecting rod big ends checked for sizing and corrected if needed....you dont want a rod bearing failure on that nice rebuilt crank...machine shop job
Swap the pistons onto your rods...machine shop job
Have the cam bearings replaced...machine shop job

What cam are you going to use?
Lifters?
Oil Pump?
Timing chain and gear set?
Head bolts?

If you dont want to do it the way it should be you should be prepared to redo it again.

Maybe a crate engine may be a better choice for you...

Just my ten cents worth....

[Happy_dan]

Thanks for all the input. The truck ran fine before I took it apart and although I don't want to cheap out, I also want to keep a reasonable budget on the project. All great advice, I'll assess exactly how far I want to go on this.

[68post]

One of your original questions was about a +.030 overbore - this requires new +.030 pistons and rings. When a "re-hone and rings only" is done you may need/or want to use file-fit rings if your pistons are still within spec and can get away with it.
You don't want excessive rings gaps !
Are you replacing the cam/lifters/timing set , or oil pump ? These are all cheap parts.

How high is the mileage of the 327 ?

There's glory in returning a good old soldier back home also.

[Happy_dan]

No, sorry for the confusion!! Not going .30 over. Just honing myself and new rings. Did a wet and dry compression test and a couple of cylinders were a little weak so new rings. That is what got me started down this road. I believe if only has 48k miles on it but can’t be sure. Truck frame and body sure look great do I don’t think it’s 148k and bores don’t have much wear etc. it does look like a lifter was replaced. I will replace all main bearibgs, rod bearings, oil pump, timing set but cam looks good. I am thinking about cam and lifters

[71cadc10]

if you are not boring the block, you want STD ring set yes.
filing gaps may still be needed, you will want to check the rings gaps

[68post]

Originally Posted by Happy_dan

No, sorry for the confusion!! Not going .30 over. Just honing myself and new rings. Did a wet and dry compression test and a couple of cylinders were a little weak so new rings. That is what got me started down this road. I believe if only has 48k miles on it but can’t be sure. Truck frame and body sure look great do I don’t think it’s 148k and bores don’t have much wear etc. it does look like a lifter was replaced. I will replace all main bearibgs, rod bearings, oil pump, timing set but cam looks good. I am thinking about cam and lifters

That low of mileage - you should come out in really good shape on this.

[Myself]

Are you sure of that 3.976 measurement? Because, as stated, that should be a standard 4" bore........meaning ALL of your measurements should be over that. That would tell me your gauge is off a bit, and if that's the case you have some clearance or out of round as much as .025". Typical of an older block ready for an overbore. My rule of thumb is less than .010" worn or out of round can get a hone and new rings.

[Happy_dan]

I used a telescoping bore guage then a caliper so I am sure it's not 100% accurate but I am thinking they are pretty consistent in the way I measure.

I need to use a different gauge my machinist neighbor gave me to borrow.

These are the measurements as done with the method I described.

Bore TX TY MX MY BX BY
1 4 3.986 3.986 3.981 3.997 3.992
2 3.999 3.989 3.94 3.968 4.004 4.003
3 4 3.996 3.985 3.999 3.976 3.995
4 3.999 3.999 3.998 3.999 3.975 3.977
5 4.002 4 3.995 3.995 4.01 3.976
6 4.001 4 3.989 3.998 3.997 3.997
7 4 3.994 3.995 3.995 3.994 3.997
8 3.999 4 3.996 3.997 3.967 3.999


TX= Top X axis, MX would be middle and BX bottom
TY= Top Y axis

X axis is Front to back
Y axis is side to middle

I did measure cylinder number one with my neighbors gauge and was right about 4.01 to 4.03 across the whole thing. So I can be reasonably sure about my others being at least in spec. Certainly looks like bottom is worn slightly more than top as expected. There is really NO ridge at all on top, nothing I can even feel or measure.

If anything, the way I measured is about .003 more than I show. That means even the 4.004 measurement I have is really 4.007. I know this is not exact science but I am thinking I will be ok.

I will measure skirts, large end, play will certainly set ring gaps and file to spec.

[AussieinNC]

Beg or borrow a bore dial indicator and measure 2 ways, along crank centerline then at 90 degrees to the centerline.
Measure at the top of the bore and bottom of piston travel....

Check piston ring land wear and skirt clearance in each bore...
Check piston ring land back clearance and land side clearance....

If the block measures ok, and the piston ring lands measure ok, then check each piston skirt clearance....

See http://blog.wiseco.com/ring-grooves#...0ring%20groove.

If they all come up within spec then just use new rings and a good hone.

After the hone, check each ring end cap in each bore approx 1" down the bore,,,,

Have fun