The Stovebolt Site Forums The Shop Area Engine Shop 216 Miss

I am trying to get the 216 from hell running properly. I have rebuilt this engine with 60 over bore and pistons, line bored, valve job, rebuilt the Carter YF carb and am still not satisfied at all. It starts and runs and has compression now in the 85 to 100 pounds range on the dry test. all increase with the wet test. engine is still not completely broken in, has just been run in place. Oil pressure and temperature perform well. It starts , runs idles and accelerates well, but does not seem at this point to have the power I expected. Problem is that is backfires when I run it at a higher RPM. Sounds like one cylinder may not be right. It runs at the higher RPM and periodically backfires out the exhaust, and once through the carb. I am also seriously considering dropping the pan and checking the bearing clearances as well. I have a slight knock/noise I don't like too.

Question is what would cause the backfire?

Absolutely sure your timing is spot on? Since it accelerates ok and seems to backfire at higher rpms you might have the valves a bit tight. Just throwing out ideas. Good luck🛠

Yes on the timing and the valve adjustment was checked recently. Distributor rebuilt too.

If a rebored engine with new piston rings has a 15 pound variation on compression pressure somebody needs to turn in his "machinist" card for one that reads "Mr. Badwrench"! I'm also going to make a guess the valve guides are fitted WAY too tight and your backfire is being caused by intermittent valve sticking. Far too many so-called machinists fit 216/235 valves to "modern" clearances, and that just doesn't work on engines designed in the 1920's. Did you fit the Babbit rods properly, using Prussian Blue and a bearing scraper, and then set the oil clearance with shims?
Jerry

I thought the same thing on sticking valves. The compression may not yet be correct. The engine is not broken in or run under any stress. The readings are higher now than the last time I took them and increase again when taken wet. No I did not scrape any bearing/ Babbitt

Just as a matter of asking, how did you "line bore" this 216 motor, and what have you done with the distributor, other then points, condenser, rotor and cap?

It was done at a machine shop , same time as the boring and head work. I took the distributor apart, cleaned it reassembled, put in a spring and spacer behind the grease cup and made sure the numbers on the distributor matched the block and that the cam numbers were correct for the block.