I'm building a motor for my Mustang and ran into some clearance issues. Exhaust valves are hitting the pistons. I think I may have just been a dummy and over tightened the rocker arms down but wanted to see if there are any experts that can help me decide if that's what I did or not? I know the right answer is put some putty in there, slap it back together, spin it and then pull it back apart but I have hydraulic lifters and I don't really want to order solid lifters just to test it.

First question, whats the stock pushrod length on Ford 289s? I seem to get mixed answers when I google it. The length I have in there is 6.805".

Motor is a 289 block with a 331 stroker kit. Flat top pistons with 5 cc valve reliefs. Cam is pretty mild at .500 lift for int/exh. Nothing "crazy". Lifters are the matching set that came with the cam, hydraulic. .040 thickness headgasket and I had the block decked down to .005 to help me get some compression with the 60 cc heads and the flat tops. I know clearance is tight with the decking so I think its a combo of over tightening and maybe slightly too long of push rods? I couldn't use a push rod length checker because the guide plates got in the way of the adjustment nut. I put sharpie on the stem and the rocker was rubbing on the outside third of the stem so again, slightly too long if I understand it correctly. I was a bit anxious to get this thing started as it's been a long process. I figured get it fired up and then I could swap the push rods out after the test fire before they wore the stem in a funky way. Lesson learned.

I pulled the heads and pistons are in good shape. Valves seem to be fine but I'm going to have them checked while it's all apart anyways. Push rods seem to have took the beating.

My thoughts at this point are to put a thicker headgasket in to get some extra space. I'll lose a little compression but I'll still sit at 9.6 if I jump up to a .080 HG. It's just a street motor so no biggie really. The extra insurance room is worth it at this point, in my opinion. Also going to get the shorter push rods like I should have done to begin with.

Any other thoughts by someone that has more experience on this sort of thing? Any glaring issues that I did wrong? The exhaust valves are the ones that hit. The intakes seem to have been fine.

I'm sticking to Chevy's from now on.