small nicks on piston and head

[owen94]

Hello, Im in the process of rebuilding my m20. the motor has 185 000 miles on it and it seems to have a loud tacking coming from the 2 cylinder intake valve so I pulled the head off and this is what I found. There seems to be small nicks on the piston with corresponding nicks on the head. The nicks are worst on the the second cylinder. Does anybody know what can cause these nicks and how it might be related to the tacking noise.

[Madhatter]

Looks like pinging/detonation.

[whodwho]

Something was in there causing that, pinging will be more of a sand blasted appearance.

If it was still making noise when you pulled the head dig around and you will probably find something imbeaded in the piston/head.

[EatsHondas]

That looks like predetonation to me. If your engine was in proper time upon teardown, you're not experiencing a mechanical problem. Where do you get your gas from? Do you have a chipped ECU? What grade of octane do you normally run? Does/has your car sat for an extended period of time?

[owen94]

That looks like predetonation to me. If your engine was in proper time upon teardown, you're not experiencing a mechanical problem. Where do you get your gas from? Do you have a chipped ECU? What grade of octane do you normally run? Does/has your car sat for an extended period of time?

I get my gas from petro canada and I only run 91 octane. No chipped ecu, everything is stock. I have only owned the car for about a year and haven't put much mileage on it.

[997_rich]

Doesn't look like pinging to me. It looks like mechanical damage from a small rock or something that fell into the chamber. It bounced around in there for a while and eventually made it's way out the exhaust valve. sometimes rocks get in like this when people clean the spark plug well when they change spark plugs.

usually this kind of occurance does more damage to the valve train than the piston/crank. the valve train is much more delicate.

before you pulled the head, did you do a compression test or leakdown? where you able to set the valves well? the loud ticking can be a bent valve (do you see one that's not seating well?) or maybe a bad valve guide. once you remove the valve springs and keepers you can check to make sure the valves don't joystick around in the valve guides. How do the cams and followers look?

[997_rich]

any scrapes in the accompanying cylinder walls?

[owen94]

Doesn't look like pinging to me. It looks like mechanical damage from a small rock or something that fell into the chamber. It bounced around in there for a while and eventually made it's way out the exhaust valve. sometimes rocks get in like this when people clean the spark plug well when they change spark plugs.

usually this kind of occurance does more damage to the valve train than the piston/crank. the valve train is much more delicate.

before you pulled the head, did you do a compression test or leakdown? where you able to set the valves well? the loud ticking can be a bent valve (do you see one that's not seating well?) or maybe a bad valve guide. once you remove the valve springs and keepers you can check to make sure the valves don't joystick around in the valve guides. How do the cams and followers look?

I did not do a compression test or leakdown test but I did have all the valves adjusted within spec and I even tried having them set a little tighter but it did not fix the sound. the head has also been rebuilt at some point ( possibly in 2003). the cam has no wear on it and the rockers are the updated stronger ones (with 03 stamped on them, not sure if that is the year or just part number or something) the head itself is still the original 87

[owen94]

any scrapes in the accompanying cylinder walls?

there is some scoring on the cylinder walls but nothing to bad

[997_rich]

I'd look closely at the valve train and disassemble to check for play. the bottom end is most likely ok but you can always pull the oil pan and check the connecting rods to see.

[owen94]

will be pulling head apart either today or next week sometime, will keep you updated if I find anything.

[Madhatter]

Something was in there causing that, pinging will be more of a sand blasted appearance.

If it was still making noise when you pulled the head dig around and you will probably find something imbeaded in the piston/head.

It will look like someone took to it with a sand blaster when it gets really bad, otherwise it looks like this, almost like someone took a small drill or pick to the chamber and piston. Look at where it is, right on the squish area while the rest of the chamber (and piston) seem to be perfectly fine.

[whodwho]

Thats where the interference area from head to piston is, look how the aluminum is displaced around the pits and not erroded. I bet there is an exact matching pattern on the head to the piston as well.

[Cabriolet]

this is a very common issue. it's from debris getting into the cylinder getting smashed around and then getting ejected. about 1/3 engines i pull apart have this issues to varying degrees. you can just smooth them out and put it back together.

make sure you get the head machined flat, pressure tested, check/replace guides and block honed.

[owen94]

so I tore the head down today and found that a chunk of the head around the 2nd cylinder intake valve guide had cracked and fallen off and also the rocker for the 2nd cylinder intake valve is extremely worn (probably causing the tacking noise)