I'm in desperate need of some ideas guys. I built the engine for my T/A racecar (everything new, including the heads) and the first time I fired it up to break the cam in, it ran great for about 8 minutes until it reached operating temp. Then it totally fell on its face and bogged way down so I shut it off. Keep in mind this is idling at 2,000+ rpm with no load. Started it again the next day, did the exact same thing. Turns out, the valve guides were loose in the heads and I had at least 1 exhaust valve stick (1 touched the piston and bent it slightly). So I pulled the whole thing apart, took the heads back to the machine shop who replaced all the guides (cast iron heads) with oversized bronze guides, diamond honed them out slightly larger, replaced the bent valve, new seals, new valve job, etc.
Last night, I finally got it all put back together and started it again. Once again, ran great for a few minutes until it got hot, then fell on its face again and bogged way down until I shut it off (still breaking the cam in at 2,000+ rpm). Then about 4 seconds after I shut it off, I heard what I'm sure was a valve snap shut on the same bank as the one that was bent last time. I pulled the valve cover immediately to check valve lash, and all the closed valves were still in spec. The motor has about 20 min total run time on it. I checked the lifters and cam last time I had it apart and no wipe lobe or lifters yet.
Does anyone have any ideas what could be causing this? It sounds like I will be pulling the heads again :frown2:
Engine Specs:
.030 over 289. Zero decked
Procomp iron heads milled to 54cc (10.15:1 CR)
Bronze guides, viton valve seals (proper clearance)
Stainless valves
Comp 294S cam (Almost .250" piston to valve clearance)
.030 MLS head gaskets
Comp valve springs (inner spring removed for the break in and no issues with coil bind)
Comp gold 1.6 rockers set at .022" lash
Initial timing set at 12 BTC for break in
Ignition is Summit CDI and billet magnetic distributor
Holley 600 CFM carb, .5" phenolic spacer, Summit 80 GPH mechanical fuel pump
Last night, I finally got it all put back together and started it again. Once again, ran great for a few minutes until it got hot, then fell on its face again and bogged way down until I shut it off (still breaking the cam in at 2,000+ rpm). Then about 4 seconds after I shut it off, I heard what I'm sure was a valve snap shut on the same bank as the one that was bent last time. I pulled the valve cover immediately to check valve lash, and all the closed valves were still in spec. The motor has about 20 min total run time on it. I checked the lifters and cam last time I had it apart and no wipe lobe or lifters yet.
Does anyone have any ideas what could be causing this? It sounds like I will be pulling the heads again :frown2:
Engine Specs:
.030 over 289. Zero decked
Procomp iron heads milled to 54cc (10.15:1 CR)
Bronze guides, viton valve seals (proper clearance)
Stainless valves
Comp 294S cam (Almost .250" piston to valve clearance)
.030 MLS head gaskets
Comp valve springs (inner spring removed for the break in and no issues with coil bind)
Comp gold 1.6 rockers set at .022" lash
Initial timing set at 12 BTC for break in
Ignition is Summit CDI and billet magnetic distributor
Holley 600 CFM carb, .5" phenolic spacer, Summit 80 GPH mechanical fuel pump