What does spark knock sound like?

[kwoods]

I've got a G that I believe is pinging when accelerating but I'm not totally sure. I've never heard spark knock before so I may just be paranoid. I'm running 93 pump gas and when speeding the engine up I can hear a weird noise for a split second before it gets up to speed. I'm not sure if I'm being paranoid or not. Engine has .125" M&W style pistons that come about .125" from block deck at TDC, cyclone head shaved about .300", competition ground cam, stock stroke, stock carb and a mag. When I put it in high gear and hold the brakes I can't hear the noise but the engine is pretty loud at that point also. Is spark knock able to be heard from the seat over the engine? I don't want to load it for too long and end up ruining the pistons.

 

[JDEM]

Retard the timing and see if that knock/ping goes away. IF it does, you will then know for sure it is spark knock/detonation.

IF it does NOT go away, it still may be. I have no idea how high a mechanical compression ratio you are running.

I once rebuilt a John Deere 2020 gas tractor for a customer and he insisted on using high-altitude pistons. This in a area with a 300 foot
altitude. That tractor had spark knock no matter how we retarded the timing. Mostly when revving it up. Not even with 100 octane aviation
gasoline did it get better. We finally tore it back down and put standard pistons in.

 

[susandiane]

In the "good old days" of run what you brung car racing, timing was often set so that there was a little ping what you got on it really hard. That never seemed to hurt anything, but those were the days of
leaded gas too. To replicate that on a tractor you'd have to have a load on it like a plow in the ground so that the governor would open the throttle fully. I'd take the suggestion of backing the timing off
to try and make it go away, then get as much as you can without pinging/spark knock under any circumstances.

 

[kwoods]

I forgot to mention this but unfortunately I have the timing as retarded as I can get it. I had a timing light on it and I am at about 30 degrees BTDC. The governor to cam gear mesh is correct because the mag drive lug is horizontal when the flywheel is in the correct position.

 

[D-]

That doesn't sound retarded. If that's as close to TDC as you can
get perhaps you can rotate the shaft a tooth.

 

[Mike(NEOhio)]

TDC is static timing. The mag will give you the 30 degrees BTDC when it's running. What you see with the light.

 

[Drew]

If your pistons are .125" down from the deck, then you have cut about .300" off the block. From the information you have given, I come up with +/- 9.8:1. That's not going to work on 93 octane pump gas. You need better fuel.

 

[MSD]

Have you tried adjusting the load needle to give it a little more fuel? It should just have a puff of black at idle and it will be about right.

 

[WeirdDeere]

I've only heard it a few times, never knew what to listen for but when I heard it it was unmistakable. Running a D with straight pipe on kerosene...so loud when plowing. I could hear a metallic pinging over the straightpipe exhaust. My cure was easy, yours, I dunno

 

[jd man wis]

My dad had a G that did the same and it was do to with the low octane fuel. If we made it ping to much it would blow the spark plug end off them an would not start the next day and we would have to change them. The boys and I built a big A for pulling and we need to run VP 12OR 16 or it will ping. With all the work done on the G you have you are going to need good high octane fuel to work it. You can get by with running the other 89 fuel for just running around.

 

[Mike(NEOhio)]

That's why they had the water valve, but you couldn't use it with antifreeze.

 

[David G]

Sounds like a good time for water injection.

 

[WeirdDeere]

Yep I opened up the water valve. I filled the cooling system up with water temporarily for that reason.

Brandon

 

[36 A]

Race gas ! mine did the same thing with a similar build . Even took the head gasket once .