Grout vs. Devcon
By David D.I.L.L.I.G.A.S
Hold on a second Pat, that’s not correct….
I think you might be confusing grout based block fillers used these days (masonry/aggregate), with epoxy based block fillers like Devcon (resin/plastic) from many years ago. The grout based material used for block filling these days is kinda based on the expanding anchoring grout/cement used to anchor bolts into a concrete floor to bolt down a piece of heavy equipment. It’s the epoxy/resin/plastic based fillers (like Devcon) that are said to supposedly deform/relax some as engine temps rise, and not grout.
I have never ever had a grout based filled Cleveland block ever split a cylinder wall. And don’t mistake grout for “regular” concrete, it doesn’t shrink as it cures like concrete does. It expands a little during curing and if mixed/poured/setup correctly does apply some pressure to the cylinder wall to help support it. Some grouts do a better job of matching cast iron’s heat expansion rate than others (depending on what aggregates are included in a company’s mix). I know from personal experience that grout does a great job of supporting that part of the cylinder wall it’s around & helps to keep it as round as possible. I know this because on teardown when re-honing a cylinder again I always saw a very nice looking pattern left on the cylinder wall where it was supported by the grout, and a worse looking pattern on the un-supported part of the cylinder wall. This made a believer out of me that (A) grout does a great job of holding the supported part of a thin cylinder wall very round, and (B) nitrous/high cylinder pressure does move the un-supported part of a thin cyliner wall around a given amount.
I have split many unfilled/no grout Cleveland cylinder walls over the years with both flattops & domed pistions (all with 4V CC heads). None were ever bent/broke valve or broke piston (or any other assorted shrapnel) related. I assume all were most likely either high RPM related, or high cylinder pressure related (from high compression numbers, or nitrous use) ….or all of the above at the same time. Nitrous does create a scary spike in cylinder pressure numbers at the hit, especially if you bang a big system and don’t have the RPM’s high enough. On all of my split cylinder walls the crack direction ran top to bottom, never around the circumference of the cylinder. Most crack placement was either somewhere in the middle area of the cylinder, or top to middle, but none ever ran anywhere near the bottom of the cylinder. I had one block split a cylinder, had it sleeved, and the next outing it split the cylinder right next to the sleeved one. Then when fixing the second split the jackazz installing the sleeve cut the block/installed the sleeve off center & crooked, aaaaand the block was junk after that. The head gasket wouldn’t seal for crap against the top of the off center sleeve, and the bottom of that sleeve leaked water like a sive. Plus the weakened deck surface from all the removed original cylinder wall material for the two sleeves didn’t help matters any either (the jackazz believed in using thick sleeves).
Knowing what I know now if I was to build a stock block Windsor based Cleveland headed engine that was going to see “racing only” use I would always want to add grout filled allmost to the top. On a street/strip combo that made less power (but still a decent amount) I would still probably want to add some amout of grout. And on a low compression crap pumpgas street/highway use (no nitrous, low RPM’s) “street rod/crusing/play toy” I would probably not use any grout & take my chances.