Valve lapping, latest verse

If'n you really wanna check your rings, ya gotta do a leakdown test, which takes specialised equipment and external airpressure source.

As long as your engine starts, runs, and doesn't oilfog the neighbors mosquitos, I'd leave it. Ya can buy alotta oil for cost of un-necessary engine rebuild..... ....Dell

Replacing the rings is cheap and easy, once you have the piston out. You have evidence of poor oil control from the smoking, though this could be coming from worn valve guides or valve guide seals. Presumably you checked the stem clearance as you were lapping the valves.

Check the side clearance between the new rings and the ring lands in the piston. A lot of times, the piston is badly worn in this area. New rings will have trouble sealing if the side clearance is excessive. New pistons are fairly cheap.

Check the piston to cylinder clearance with a feeler guage. Check the ring end gaps as well. Out-of-spec piston clearance may be uncorrectable bacause of wear in the sleeves, but you can live with that in a "quick and dirty stop the smoking" rebuild. But you might consider buying oversize rings and filing them down to correct the end gap, rather than living with the excessive gap likely to result from putting new stock rings into worn sleeves.

As I found it, the engine had no valve stem seals at all, but the guides were tight. I put 4 new stem seals on the intakes and struggled to get the square edged seals past the square edged lip on the bore for the guide.

I tend to agree with you that it seems unlikely that manifold vacuum would pull a lot of oil uphill past the guides on a flathead. But it may be possible if the situation is bad enough.

A couple more checks to consider when trying to find the source of the smoke:

If the smoking gets worse under load (low vacuum), it's rings. If it gets worse at idle (high vacuum), it's the guides. Also, pull the breather cap off and see if the crankcase is under a vacuum at idle. Really bad guides will do this. If, on the other hand, there are puffs of blowby out the oil fill tube, you can suspect ring leakage.

The side clearance on the 4-ring pistons in the original engine was very high (.020+), so I opted for new sleeves and pistons even though the originals looked OK visually. The rebuilt engine is nice and tight -- no smoke or blowby and good power.

I don't see anything inconsistent in the FO-4 manual about side clearance. Paragraph 34 on page 31 gives a wear limit of .004. Later on (page 32), it gives a new spec of .0015 to .0035 for the top ring, .0015 to .0025 on the second ring, and .0015 to .0030 on the oil control ring. The top ring is the most important one.

I'd probably let the side clearnace go up to about .006, but too much more won't seal properly -- a lot of the sealing comes from combustion pressure getting behind the ring and forcing it into the cylinder wall. Too much side clearance and it will just blow out the other side. Your compression rings also provide a good deal of your oil control, and if they don't seat under power, the engine will smoke.

The top of the sleeve is the primary wear area due to compression pressure against the top ring. No surprise the sleeve is worn to a bell-mouth. Squaring it up is more important than maintaining skirt clearance -- I wouldn't worry about taking off .001 or .002.

The top ring has more trouble following a bell-mouthed sleeve -- spring pressure alone isn't enough. It needs compression pressure to help. This makes the ring-to-piston side clearance more critical.

I don't think there is even a spec on the tightness of the studs in the block, as there isn't a seating face on the block end of the stud to create tension in the lower threads and thereby create a reliable recipe for torque.

If I were to re-use the studs I'd goober up the bottom threads with non-hardening teflon pipe thread sealant. Screw them into the block until the installed height looks right. Don't worry about torque on the bare studs. Wipe off any sealant from the top of the block and the top threads of the studs. Put the head on. Tighten the nuts to the torque spec. It won't matter if the stud turns a bit as you torque the nuts; the sealant will re-seal around the threads after the stud turns.

My preferred recipe for the head is the following:

1) Genuine FNH composite head gasket 2) box of 7/16 14 x 2 1/2 inch grade 8 cap screws 3) box of 7/16 grade 8 SAE washers 4) Can of teflon thread sealant

Items 2) 3) and 4) can be had from a place like Ace Hardware for a total of $12.00 or so.

Put the head gasket on the block with the rolled edges up (toward the head). Do not use gasket paint.

Coat the bolt threads with the sealant. Install the bolt and washer into the hole and start the threads. (Do not use a washer if there is to be a bracket under that particular bolt head). Wipe any sealant off the bolt head and washer -- it will throw off the torque later if you don't.

Torque the bolts in 3 steps in the proper sequence to a total of 53 foot pounds. (The torque spec is adjusted downward from the 70 ft-lbs "clean and dry threads" spec to allow for the lubricating effects of the sealant on the bolt threads.)

Exactly what I was thinking.