350 not running right spark plugs hit....???Compression test results

[Reumster]

I took the heads off my motor, and there you have it the upper ring of the pistons are breaking off! I dumped a little oil and did a copression test and the pressure on #4 cylinder jumped from 100 to 180! So I knew before removing the heads what the problem is.

Now for my *****ing, this is the second set of KB Silvolites that I had the upper ring of the piston break! I'm calling the place that built my motor and *****ing. They should have known that the upper rings on them pistons need special filing and gap. So what could cause the pistons to break like that? Would over heating the motor do that? Running it lean??

What cheap pistons would you guys recommend? And I think I'm going to use regular rings, not chromoly this time.

Here's my question the valves can't be bent or messed up if the pressure climbed like that can they? So I think maybe a lap job and use them. Maybe get a vacum test too.

[wlee]

If a piston hits a spark plug, it has hit other components along the way . . . carbon can build up and cause some knocking, but you would have fouled plugs by the time you hear the noise.

An old Chevy garage trick for carbon build-up is to start the engine with air cleaner off - get a bottle of water and pour it slowly into the carburetor with the engine revved to about 1500 rpm. The engine will try to die - stop pouring the water & wait for the engine to recover. Repeat one more time & your carbon build-up will be gone. This works by the water turning to steam vapor in the combustion chamber which will burn the carbon off the piston top.

I would be surprised if this is really your problem . . . you may have a "long" plug installed, but ALL of them should be getting hit - if only 3 are hit, you may have a carbon build-up.

The platinum plugs are designed for fuel injected engines that have a more uniform fuel burn pattern - the old carbureted systems are usualyy dumping erratic amounts of fuel in the chamber that tends to foul the platinum plugs. Good Luck!!

[Blazer1970]

All of your problems (broken plugs and broken pistons / rings) are caused by spark knock. If you do not fix the problem (too much compression combined with too much timing advance), no piston, ring or spark plug is going to last in that engine.

[Reumster]

So how do I tell if I have spark knock, and would it help to use dish pistons to lower compression ratio? Or how do I tell if my timing is to far advanced? When I put new pistons in I don't want this to happen again. The motor has very low miles, so I think I'm just going to hone the walls, new pistons and rings, and put a new oil pump in and put it back together. Any recommendations for a good oil pump?

[Blazer1970]

I noticed a bad valve train noise and it would want to die, then it would just stop.

This is a quote from one of your posts in "engine and drivetrain". I am guessing that what you were hearing was spark knock, not a valve train noise. Spark knock sounds like a high pitched metal on metal sound - kind of hard to describe, but once you know what it sounds like you won't mistake it for anything else.

I was trying to find the chamber volume of your Trick Flow heads, but no luck. Do you know the combustion chamber volume? What kind of distributor are you running, and how much initial advance? It seems like you should be OK with flat tops unless those heads have a very small CC. Most likely you are just running too much initial advance, or you are getting way to much mechanical advance way too soon.

[Reumster]

I'm running 68cc heads, and 40 over. I'm going to go to dish pistons. I'm using a new accel distributor & super coil. If I were time by ear how would I set the timing at a good spot.

[Blazer1970]

I would buy, beg or borrow a timing light if I were you. Setting your timing by ear when you are not sure what spark knock sounds like is a recipe for disaster.

[cali_surfer]

I bet the holes in those Trick Flows are 14mm x 3/4". Thats what the hole size is on my Edelbrocks. If they are a washer seat, R45 work good