Vavletrain instability small Block

[Joe C.]

Re: Vavletrain instability small Block

Jerry said that he removed the stem seal from 5E to ensure a greater supply of oil down that stem. He also increased guide clearance on 5E to allow for more expansion. It's possible that 5E valve seat is too narrow...............maybe .030 - .040 rather than an acceptable .060 - .080, and not allowing enough heat to be transferred to the seat from the valve. Possible, yes. Probable?????

Sounds more like an oiling problem to me. He sees oil coming out the 5E pushrod at low speed, but maybe not enough at high speed. Excessive bearing clearances stealing too much oil from the top end to the bottom end? If so, then will need a high capacity (volume) oil pump. Open up the drainback holes in the lifter valley for faster drainback to the sump. Try using edge orifice lifters in the other 15 and a piddle valve type in 5E. Oil supply to the top end might be right at the "ragged edge" and it just so happens to show up on 5E first.

[Ken A.]

Re: Vavletrain instability small Block

i was trying to clarify that the problem valve is #5 exhaust not intake. I was running roller tip and trunion at Portland so no ball to examine. My worry is that I'm going to Monterey and i will be running stamped rocker and ball. The chatter marks on the pushrod would have closed off the oil tube if it had continued which would have led to failure. i have to believe its a heat problem that is causing this. I opened up the guide clearance and am not running a seal to make sure that wasn't causing problem. i also route coolant into head from water pump to help cool this area.

Are you using aftermarket chromemoly pushrods or stock GM parts? Back in the day we had to order 50-60 GM pushrods to find 16 straight ones. Today's chromemoly Lunati p/r's are about bullet proof. Also, GM recommends that when you replace an exhaust rocker assembly that you use a "run in" intake assembly. Always use the new rocker on the intake valve.
Your cam selection is not an issue.

[Jerry G.]

Re: Vavletrain instability small Block

I,m using Comp Cam 7995 5/16 Chromoly. I ran bench tests on the FI unit with graduated beakers to insure equal flow to all cylinders. I also have an A/F monitor on the left side to insure A/F doesn't change or get to lean. Running about 12:1 to 13:1. I like Clems idea of changing this cylinders timing, very clever.
I have also tapped a 3/8 water feed into the 3-5 exhaust area in the cylinder head. Has anyone else done this modification. i think it helps but I'm trying to figure this out.

[Jerry G.]

Re: Vavletrain instability small Block

that cylinder could be running a little hotter than the others . you can change the timing in that cylinder by shimming the plug outward,.020 changes the timing about 1 degree

Interresting...Very interesting. How much differeence in temperature will this make? i just have no feel for what a 1 degree change does.
You are a wealth of expirience.
What do you think of routing water into 3-5 exhaust location of cylinder head.?

[Clem Z.]

Re: Vavletrain instability small Block

Interresting...Very interesting. How much differeence in temperature will this make? i just have no feel for what a 1 degree change does.
You are a wealth of expirience.
What do you think of routing water into 3-5 exhaust location of cylinder head.?

can not say for sure and a dyno run with thermocouples in the headers will tell. i have seen sprint car engines were they tapped into the block between 3/5 and 4/6 for better cooling. make sure all the water passages in the head and block line up with the holes in the head gasket as i have seen some the holes in the block had to be modified

[Clem Z.]

Re: Vavletrain instability small Block

can not say for sure and a dyno run with thermocouples in the headers will tell. i have seen sprint car engines were they tapped into the block between 3/5 and 4/6 for better cooling. make sure all the water passages in the head and block line up with the holes in the head gasket as i have seen some the holes in the block had to be modified

another thing is that the exhaust port that has the heat riser crossover passage. if it is i would fill the passage with high temp furnace cement so that opening is not there and holding exhaust heat.

[Jerry G.]

Re: Vavletrain instability small Block

another thing is that the exhaust port that has the heat riser crossover passage. if it is i would fill the passage with high temp furnace cement so that opening is not there and holding exhaust heat.

They are stock heads from the period that have been extensively ported and relieved so I would suspect that the heat riser passages are there.

[Ken A.]

Re: Vavletrain instability small Block

Jerry,
Any chance you're running a 377 incher or a 330? They produce more heat & really can run lean with the old FI. I'm going to guess you've got a bad head casting, especially with all the work you've done already. Wouldn't be the first bad head-but it is rare.

[Joe C.]

Re: Vavletrain instability small Block

another thing is that the exhaust port that has the heat riser crossover passage. if it is i would fill the passage with high temp furnace cement so that opening is not there and holding exhaust heat.

I'm not keen on the furnace cement idea, just in case it crumbles due to vibration, and/or a small piece breaks off.

This is how I did my 461 heads:


#1: Before





#2: Press fit plate steel in place





#3: Plate steel reinforced with JB Weld



It doesn't matter where you block the passage. As long as there is no flow, the exhaust gas that enters from below will stagnate within the blocked passage and cool to the temp of the surrounding casting. It makes a huge difference in the way the engine performs. My thermostat is 165 degrees, and, believe it or not, that's the measured temp of the coolant, verified with an IR gun on a sunny 95 degree day, idling on the blacktop driveway. The calibrated temp gauge bears this out, and reads consistently about 1/8" to the left of the 180 degree center mark.

[Jerry G.]

Re: Vavletrain instability small Block

It's a .040 over 327. The FI unit is far from "stock" it flows 720 CFM with rock solid A/F throughout the range. although if you look at it externally it appears stock. The FI unit design was last winters project,
I think Clem and Duke have peged it correctly as a heat problem. There is a crossover passage cast in the head. it's on the motor and i don't want to pull the heads to do the furnace cement fix. ( good idea though) i'm going to check for a casting debrie where i have tapped the head and go with spacing the plug out to run that cylinder cooler.
The radiator is a custom made unit with an integral oil cooler. It is sized for a much larger motor so the water and oil temps are fine. just this one cylinder is a problem. I have looked at the plugs and they are all good. no lean or rich ones. one other thing i'm going to check is spring pressure on this cylinder, maybe it has fallen off for some reason.

[Jerry G.]

Re: Vavletrain instability small Block

I'm not keen on the furnace cement idea, just in case it crumbles due to vibration, and/or a small piece breaks off.

This is how I did my 461 heads:


#1: Before





#2: Press fit plate steel in place





#3: Plate steel reinforced with JB Weld

VERY nice could this be done with the heads on the motor/ Do you have a template ? Jerry

[Joe C.]

Re: Vavletrain instability small Block

VERY nice could this be done with the heads on the motor/ Do you have a template ? Jerry

Yes, it can.

No template will work, as all castings have slight variations. On my heads, both sides are not the same size and shape.

I didn't do it this way, but you can use a piece of soft wood, like pine. Cut it slightly oversize and pound it into place. Remove and there is your template.

Stuff a rag tightly within each port so it blocks off BELOW where you intend to work. THOROUGHLY clean the work surface. You may use a small file/Dremel/burr to "dress" the area before making the "plug". Clean with strong solvent, like lacquer thinner to remove ALL carbon. Vacuum and remove any debris from within the port. Use needle nose pliers and remove the rag from below.

[Jerry G.]

Re: Vavletrain instability small Block

Joe since mine is an FI intake there is already a block near the head in the intake adaptor. I guess the trick is to get the plug down into the passage far enough that it would benifit the temperature of the valve guide but not too close to the exhaust chamber because it would melt. Is that correct?

[Clem Z.]

Re: Vavletrain instability small Block

you want to plug the heat riser passage down at the bottom next to the valve pocket. so the exhaust heat does not go up the passage. smoothing the opening in the valve pocket also helps the port flow better. some builders fill the passage with molten lead but i have no problem with high temp furnace cement

[Clem Z.]

Re: Vavletrain instability small Block

you want to plug the heat riser passage down at the bottom next to the valve pocket. so the exhaust heat does not go up the passage. smoothing the opening in the valve pocket also helps the port flow better. some builders fill the passage with molten lead but i have no problem with high temp furnace cement

the poured in lead was bill jenkins answer to the problem