Running Rough

[Gene Fiore]

I went to the track last night and the car was running really good. The night air was cool and I ran some of my best times in time trials...15.25 and 15.26...all was good. Then first round came around and I dialed a 15.25 but lost the race to a 10 second car at the stripe. I stop to get my time slip and it is idling pretty rough and the car slowed to a 15.42 on that pass. I check the carb and timing at the track but still idling rough. This morning I pulled the plugs and they all looked pretty decent...a few were a little dark. I pulled the valve cover and everything looked fine. I decided to check the valve lash and every one was quite tight...couldn't even get the feeler guage in there. So I re-adjusted all the valves, check air fuel and timing and it is still idling really rough. Now what? Could a blown head gasket between adjacent cylinders be causing this? Is there a way to tell without pulling the head?

 

[69.5Mav]

Is there a way to tell without pulling the head?

Plugs are already out, run a compression test.

 

[bubba22349]

X2 a slightly blown head gasket will show up with two lower reading cylinders next to each other.

 

[wsa111]

Gene, pull the plugs & do a compression test.
If that checks ok check for a vacuum leak carb or adapter area.
This is a long shot, but check for debris in the idle jet & or main jet.
Check the valve springs for a broken one.
See of you can narrow it down to a perticular cylinder. Good luck, Bill

 

[tri-power 250]

Gene,
Check your distributor cap and rotor button.
Good luck
Ken

 

[JackFish]

And check to see if you haven't blown out your balancer.
I had a relatively new one from Damper Doctors go out on me.
They replaced it under warranty.

 

[thesameguy]

If the valves were too tight, is it possible an exhaust valve got burned?

 

[Asa]

Can use shop air to check for a busted head gasket
Put at least 100PSI to each cyl with the valves of that cyl closed. If the coolant tries to bubble up out of the radiator it means that air is getting into the coolant system, if you hear it from the cylinder next to it you've got a blow out between them

 

[Mustang_Geezer]

I'd go with vacuum leak 1st and junk in the carb 2nd. Either one has happened to me more than once!

Later,

Doug

 

[Gene Fiore]

UPDATE: This morning I did a compression test and the results are disappointing. The number 1 cylinder is only reading 60-65 while all the others are 155-160. I'm not sure what this could mean. This is a fairly new build so I'm not sure what to think.

 

[69.5Mav]

Can use shop air to check for a busted head gasket
Put at least 100PSI to each cyl with the valves of that cyl closed. If the coolant tries to bubble up out of the radiator it means that air is getting into the coolant system, if you hear it from the cylinder next to it you've got a blow out between them

I agree. Only have to do it on cylinder 1. If air is leaking it must come out somewhere so listen at the carb, exhast, oil fill and radiator.

Easiest to fix and most likely is a burned exhast valve, next is a head gasket. Head gasket is not any harder to fix just less likely.

 

[Gene Fiore]

UPDATE: I didn't think much about the fact that the week before my issue I was racing and I kept blowing my valve cover breather off. So before the last race I replaced it with a snugger fitting one. Problem solved...well sort of...it didn't blow off any more but......when I limped home from the last race and looked at it the next morning I noticed oil splashed on the side of the block and on the oil pan and converter cover. The motor doesn't leak a drop of oil so the only place it could be coming from was the dipstick. When I told my machinest about this he told me that most likely I have broken the ring land on the number one piston and there is so much blow by going into the crankcase and forcing the oil out the dipstick. Crap! A little history is I blew the head gasket a month ago on the chassis dyno on the number one cylinder. This may have caused an extremely lean condition and hurt the piston.

 

[69.5Mav]

Crap! A little history is I blew the head gasket a month ago

Can use shop air to check for a busted head gasket

It may well be a busted ring but I would still try the shop air. It's simple and cheap.

 

[MPGmustang]

well at least it's not a piston (picturing will and kelly's), doesn't sound like it's anything but a ring, hopefully when you dive in you don't find other gremlins... Good luck Gene! and thanks for keep us posted...

 

[wsa111]

Gene, sounds like a fried piston & or rings on #1 cylinder.
Might as well pull the head & pan & pop #1 piston out & hope there is no cylinder wall damage.
When you get it back together richen the front pvcr orifice .002" larger than the rear one.
Under acceration # one cylinder is leaned out cause all the liquid fuel is pushed back towards the rear cylinders.
I believe you need to purchase an innovate A/F ratio tester so this does not happen again.
You must have gone over 14-1 or the octane of the fuel is too low or too much total advance caused detonation.
Give me a shout if necessary, Bill

 

[Gene Fiore]

well at least it's not a piston (picturing will and kelly's), doesn't sound like it's anything but a ring, hopefully when you dive in you don't find other gremlins... Good luck Gene! and thanks for keep us posted...

Breaking the ring land is the piston...if that is indeed what happened. If so a new piston will be required plus rings to go with it of course.

 

[Crosley]

I would think the head gasket blowing on the dyno was pointing to a larger problem as you have learned.

Just thinking out loud here:

Was there any indication of the problem on the dyno when the gasket blew?
Did you resurface the head then?
Did you check the head for straightness or cracks?
Head bolts or studs used on the head?

In our chats at the track I may have mentioned:

On my 200 cid engine, I have run the front jet in the Holley 2 barrel 1 or 2 sizes larger than the rear jet (carb sets sideways on engine). My spark plugs have always indicated a leaner burn on the front cylinders than the rear

 

[Gene Fiore]

I would think the head gasket blowing on the dyno was pointing to a larger problem as you have learned.

Just thinking out loud here:

Was there any indication of the problem on the dyno when the gasket blew?
Did you resurface the head then?
Did you check the head for straightness or cracks?
Head bolts or studs used on the head?

No indication of a problem before the gasket blew that I could tell. I was using a Corteco head gasket the first time but decided to switch to a Felpro when I saw how bad the Corteco looked. When the engine was assembled the block was decked to straighten if up and the head was good. Did not check the head after blowing the head gasket last month. I am using head studs. I'm wondering if my quest to solve my WOT rich condition caused the number one cylinder to go too lean causing the problem.

 

[Gene Fiore]

I finally got the head off last night and was hoping to see signs of a blown head gasket on the pushrod side of the motor...nope. Head gasket looks good but completely covered with oil. The previous head gasket was in the same condition...covered with oil. Not sure what to think of that. Also this time the top of every piston is covered with oil. Could doing the compression test caused oil to get up on top of the pistons? One good thing so far is I turned the motor over to get the number one piston at the bottom of the stroke and the cylinder looks perfect...no scoring or any signs of carnage. Just to make certain the head is ok I am going to take it to my machinest to have him check it out. Assuming that is ok then the next step is pull the motor and take the number one piston out and see what's going on there. I hate it when things break!

 

[bubba22349]

No on a compression test causeing or pulling oil unless you put a bunch of oil in each chamber when doing the test. That leaves a ring or valve guide or valve seals for excess oil. A simple way check the valve seal of the head is lay the head level with chambers up than pour some gas in each chamber if it drops down quickly or you see any wetness in the ports the valve job will need to be redone.