Engine Problem

G

grumpys hot rods

Member
I purchased this engine 5 years ago. A 49-53 engine. Have had running on an engine stand.
Starts and runs ok 19in vacuum. When I rev up the engine, It starts running bad. Pull spark plugs and the electrode is shut. Looking thru spark plug hole
Can see where the valve has been hitting the spark plug.

CHAMPION J12YC AND AUTOLITE 216

Wrong Spark Plugs?
 
I believe the "J" series threads are ok for clearance...actually a bit shorter than the correct H10 Champion threads...BUT the "Y" suffix means extended tip and that may be a problem as the valve opens enough to hit.
Are the Autolite 216's being hit as well? They should be ok with a stock head unless the cam has a LOT of lift.
 
The Autolite 216 Plugs are also hitting. I'm going to try 216 with two washers and see if that works.
I tried to measure the valve lift. The valve comes real close to the cylinder head.
I'm thinking that the cylinder heads were milled a lot.
And add to the aggravation I have sold this engine to a friend.
 
Try an extra gasket. not the best idea, but should clear the valves. You'd have to mill the heads quite abit for the valves to hit the plugs, sounds like an aftermarket cam.
Gramps
 
I measured the exhaust valve lift with a dial indicator this morning.
I have .410 lift at that valve. That's a lot.
Checked flathead cam specifications and found the aftermarket cam with .400 Isky Jr
Going to try two washers this morning. Wish me luck
This is why you should check A camshaft.
 
You also can try non projected spark plugs from NGK they may work.
Used these with Edelbrock heads when I had contact with exhaust valve to original projected plug.
Phil NZ
 
The 00jr cam will have only 375/380 lift. The 400 jr has aprox 390 ;ift, and varies abit depending who grinds them. The one I used in the stock car cam from Isky I hope.
 
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What is also concerning is that it starts and idles just fine . . . which means the valves are not hitting the plugs.

Then you rev it up and the plugs get whacked and closed. If this is the case, then there may also be an issue with the valve springs . . . as the cam lifts what it does all the time and the valves should hit the plugs at any RPM - not just higher RPM . . . unless the valves are "floating".

If you're floating the valves when you rev it up, then there is nothing you can do to "fix it" with a different plug - the valvetrain is not setup correctly and the end result is too little spring pressure.
 
slowspoke said:
Could an incorrect valve lash result in this issue?
Click to expand...

Not really as the most common valve lash issue is TOO much of it.

Also, typical valve lash values for performance cams are about .015, so it is doubtful that it is just a bit too tight and causing this.

Obviously the chambers are really close to the valves (probably too close), but he may also have valve spring pressure issues.
 
I ran stock springs on most of the L-100 builds, with a .060" shim. thid brought the installed spring pressur up to about 50lbs. The engines run up to5K with no problem. Installed in a street engine that rarely sees 4K. However, you might not get away with it with the 400jr.
Gramps
 
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