The Stovebolt Site Forums The Shop Area Engine Shop A few questions about a 235 six engine...

I need a bit of information on a 235 engine I am doing some work on.
What should the piston ring gap be? The rings I took out had a gap of .120” which is a LOT bigger than I am used to seeing. The engine as a lot of blow-by and I’m assuming this is due to the large ring gap (there appears to be zero wear on the cylinder walls).
My guess would be to use a gap somewhere around .015” on the new rings. Is this reasonable? Does anybody have the actual spec from a manual?

Rod bolt torque? My guess is 45 lbs.
Head gasket torque? My guess is 55 lbs.

Should I use gasket glue on the oil pan, or just straight cork with no glue/cement at all? I used blue silicon and cork the first time I put the pan on, and it was absolute hell getting it back off, so I’d rather not use glue if only the cork will work.

Thanks for any help!
Phil

Ring gap Compression .007 Oil .015
Connecting rod 40 ft/lbs
Cylinder head 90 ft/lbs

I usually use #2 Permatex.... John

Main bearing clearance .0008 to.0026
Rod bearing clearance .001 to .003

John

Crankshaft end play .003 to .009 Thrust bearing number 3 main.
Piston clearance .0005 to .0011

Cylinder head tighten sequence....

15, 11, 5, 4, 6, 12, 16.

9, 1, 10.


17, 13, 7, 2, 3, 8, 14, 18.

As I read this a question came to mind.

....if you put a 235 head on a 261 which torque pattern do you use?

....I'm guessing that if the 235 head has the 6 "steam" holes drilled for the 261, then it'd be torqued like a 261. Comments.

I will use the 261 pattern if/when I put a "848" 235 head on my 261. Also, I do not plan on having to worry about any steam.

Have you measured the ring gap at different locations in the bore? I would be that your cylinder walls are egg shaped.

You would wonder why the pattern would be different for a 261 engine? I remember people use to if they didn't have a diagram of the tightening sequence would start in the middle and go in circle from that point and tighten the head bolts.....

John

Phil, there's a simple reason for the excessive ring gap- - - -the rings are worn out! Be sure to check the cylinder taper, either with a dial bore gauge, an inside micrometer, or by using an old ring and checking the gap at the top and bottom of the ring travel. Subtract the bottom gap from the top and divide by 3- - - -the result is cylinder taper, and it should be less than .005" for a successful ring job. Good luck!
Jerry

Edit: Another reason for a big ring gap would be using standard-bore rings in an oversize cylinder. Be sure to measure the cylinder and/or piston diameter and get the right size rings.
Jerry

thanks for all the info guys, i appreciate it!

Jerry, what difference should I see in the piston diameter vs. the cylinder diameter (i guess this would be called piston clearance?)

I'll go check the taper now...

Most pistons run about .002"-.003" of skirt clearance. Measure the piston at about wrist pin height, and 90 degrees from the pin. Most pistons are "cam ground", meaning they're not round until they reach operating temperature. For instance, a standard piston for a 3 7/8" bore like a 283 V8 will measure about 3.8735" at the midpoint of the piston skirt. An unworn 283 standard bore will measure 3.875" from top to bottom. Most of the cylinder wear happens in the top 1 1/2" of ring travel, so even a worn out cylinder will measure correctly halfway down the stroke. The rings try to maintain contact with the cylinder surface by flexing twice each turn of the crank, so a ring will be changing diameter 83 times a second at 2500 RPM in a taper-worn bore. No wonder some re-ring jobs don't last!
Jerry

Jerry,
I found about .009" difference in the bore, so /3 = .003" taper, and from what you've said, this is an ok number.


thanks for the help!

Sounds good. I assume you mean .009" ring gap variation, not bore size, right? Do a good glaze-breaking procedure with a flex hone or something similar, followed by a thorough scrubbing with HOT water and detergent like Tide or dishwashing liquid and a stiff-bristle brush, followed by several rinses. When the cylinder walls flash-rust as soon as the hot water evaporates, they're clean enough. Do a wipedown with motor oil to prevent further rusting until the engine can be assembled.
Jerry

there used to be slightly a .001" oversize of std pistons available.measure the cylinder in several places first! then they went to .020',.030",.040" but i dought you would be able to find any now some N.O.S. stuff still might be around somewhere.sounds like a tapered bore there.very common. they do have offset wristpins so they have to go in a certain direction. offset is 5/64" and you do measure them at the center of the wristpin. they are cam ground.meaning not round when at 72 degrees. piston to cylinder clearance at min is .0005"to .0011" that is with stock pistons only! they have 2 compression rings at the top and 1 oil ring on the lower ring slot.the comp rings are hastings and are cast iron the top ring is usually chrome plated. the oil rings are thin cast iron with a spring expander to keep them apart install with gaps 120 degrees apart.oil the rings and the ring grooves with engine oil.ring gap is min.007" to.020'on the comp rings and .005: to ..015"on the oil rings on a thriftmaster and .010" to .018" on the loadmaster oil rings. as a rule figure 003" gap for every inch of bore for the comp rings. this motor has a std bore of 3.620" or 3 9/16". so.003" x 3.620= .010"the compression ring are a reverse twist type the face of the ring is usually cut on a slight angle follow the new ring instructions in the ring set for installation as marking may vary from a dot meaning that side up most cast rings have no marks on them moly style rings are not usually available for this motor but total seal does make ring sets p/n 6310 but are really not nessessary for a street motor.enjoy the repair.

Yeah I remember Packard use to list .001 over pistons and even .005 over pistons available..... John