I don't post on here much... my little SOHC is hardly considered "All Motor", but I'm having some issues I think the engine building guys can help me out with.Here's my build thread on CRX Community, I don't want to copy all the posts over. So I'lll summarize:
Setup:
D16A6 block, not decked
ACL bearings
stock rods
PM7 pistons
OEM seals, 3 layer HG, belts pumps etc
D16Y8 head, ported and rebuilt
Crower Stage 2 NA cam
AEM Cam Gear
Z6 intake mani
DC 4-2-1 header
AEM CAI from 99-00 Si
Compression (static) should be about 12.6:1. I've run this before on a stock Y8 cam, I ended up taking it apart because I thought it was having a motor issue with a weird misfire, it turned out to be some loose metal in the dizzy. I know it can run and not ping on 93, but it seems everyone is quick to say the compression is too high. It should be even better now with the cam, since dynamic compression will be lower.
Anyway, I finally got it started this past weekend, and my friend who tunes it for me (Crome Pro) just made me a really quick safe map to move it around on. My AFRs are conservative, it's eating quite a bit of fuel. He's coming this weekend to tune it correctly for normal use. Anyway I put a few miles on it, and it started to knock/clatter really inconsistently just as I was getting close to home the other day. I assumed it was rod knock, though my experience with that is limited to my A6 that knocked for a few minutes before it blew a hole in the block. A few hours later, I started it up to show a friend and the knock was gone. Once it warmed up, the knock was intermittent again. I tried pulling plug wires to locate it, but it didn't seem to make a difference.
I did some reading around here and found that the LMAs can be noisy, so today I went back to the shop to check them out. I thought it would be likely because the head sat for a long time, and I didn't know to soak them in oil.
I checked the LMAs and they sprung back fine, but I took them out and let them sit in oil for a few hours, and pumped them in and out while they were submerged. Reassembled, checked the valve lash again. A couple of the intake valves were a little tight, so I got everything the same, 006 intake and 008 exhaust as per the Crower specs for the cam. Retorques all the bolts in the head, but nothing was really off anyway. Set the timing to 12BTDC. Then when it was warm I changed the oil.
I used a clean pan to check for metal flakes or anything that would indicate a bad bearing, didn't see anything. I even took the filter apart to see what was in there, what a pain in the ass. I didn't want to hacksaw it because that would put more metal flakes in there, so I mangled it in the vise and used a hammer and chisel/screwdriver. Nothing. There was a little piece of RTV, on one of the circumferential holes that's visible on the filter when you hold it normally.
I did a compression test after that, 200-220-220-200. I think the middle two had a little oil in them still, as it was on the plugs. I regapped the plugs from 025 up to 035. Started it back up and it ran smooth, the knock is again intermittent, now it's quieter and at higher RPM only when it does appear. I'm stumped! I'm going to borrow a laptop later if I can and see what my AFRs look like, but it's louder than what I've heard detonation to be with my old motor (more of a clatter than a metallic buzzing).
Any ideas?
Tom Downes
1991 CRX SiPanducky Motorsports
Central Florida's only Authorized NepTuner/Dealer
CRX Community
