Valve and compression issue

tenxal

Well Known Member
It's an NHRA Super Stock small block Chevy, '93-'94 265 cu. in., throttle body injected. The engine is a new build as a second engine for a pals race program....the dyno session is two fold. He's switching to a new Holley engine management system, so it's on the dyno for initial data gathering. Different tune up can be made and saved as files in the laptop. These can then be loaded into the engine management system for various track and air conditions. The system is also a 'self learn' system which should somewhat simplify things over the previous Holley Commander 950. Once it's sorted out on the dyno, the new system will be fitted and wired into the car.
 
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Jeffrey Osstyn

Well Known Member
Supporting Member 3
In regards to the springs, cam manufacture will recommend the spring to use. You indicated 13" of vacuum at idle, to me this would indicate a non grocery getter type of cam, or a faster grocery getter at least. Or vacuum leak. Follow the recommendation. But there is a lot more to it. You need to check installed height of spring, then what pressure the spring has at that height. Then the open height/pressure, plus a few more things. So, the new heads, are the valve stem lengths the exact same as the old? As I mentioned earlier, hours are spent checking things before anything is bolted together. The chance of changing the heads with new valves/springs and having everything just fall in place, slim at best. It never happens for me.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Wait a minute,the 93-96 265's were "baby LT1's" and were multi port injected.How is TBI legal here?
 

Jeffrey Osstyn

Well Known Member
Supporting Member 3
Old rod 40 I re-read your very first post, first paragraph about pushrods being loose with engine shutdown. This will be normal if you are checking the ones that are NOT opening valves. No oil press will allow lifters to bleed down. Do not tighten these down. I also see you used Show Cars springs, probably the ones they recommend, so good there. How did the rocker location check go?
 

oldrod40

Active Member
Supporting Member 1
Tenxal cant wait to see what HP and Torque that is putting out and what is it ran in?

Jeff, I checked the rocker arm contact to the valve on one of the cylinders that is ticking. The exhaust (not ticking) it made good contact in the middle of the valve and rocker arm (where its shiny already). On the intake it was in the middle third of the valve but two contact points so dont know if that is the rocker arm or what. Should have taken a pic of it thinking now but compared to the other it was two small contact points but in the center of the valve stem and in the shiny part of the rocker arm contact point.

I went back and changed all the valve springs to the originals off the 379 heads, adjusted and still have the same symptoms. I did the vacuum check again and sorry its 14 not 13, not a big difference but wanted to be accurate. Thats also setting the timing and the idle not being smooth like it should be. If I increase the idle a little it pulled better into the 19-20 range. I did check the valve stems and they have the same measurement on the 817's as the 379's, about 1" and 1/16 of an inch from top to the head. Maybe the intake gasket didn't seal which could cause the poor idle and the vacuum being low? When I adjust the rockers I give it a 1/2 turn when there is no lash and the pushrod slows while spinning it. They are Isky lifters and they set on the old heads this way that's why I don't understand why they wont set this way with the head switch.
 

Jeffrey Osstyn

Well Known Member
Supporting Member 3
Well, I do not have an easy answer to your problem. Need to step back and look at what is known right now. Lifters adjusted correctly, this means the pre-load on the lifter plunger is correct. Without beating this to death, we will assume it is. I hate that word, 'assume'! Given that, what can cause a 'gap' in the valve train that would give you the 'ticking' noise? Checking valve train geometry by marking the valve stems will verify correct pushrod length and that the rocker is not sliding off the valve stem. What else? Extreme cases, rocker studs pulling out, adjusting nut backing off, rocker arms badly worn, valve stem tips badly worn? Cam lobe to lifter contact area worn badly. The other more common cause, the lifters are bleeding down. Dirt in the lifter in just the right place will cause this. I have seen RTV lodged in there causing the bleed down.
One more thing you can try, as others have suggested, adjusting with the engine running. Personally, I have not done this for years, but I have in the past. Once the lifter preload is set, prior to engine run, it should never change or change very little. Not enough to cause a ticking noise. Guys who race with hydraulic lifters like to set the preload at the very minimum, this gives max valve lift. So, if you want to try this be aware it will get messy very quickly. You used to be able to buy clips that go over the pushrod ends to redirect the oil squirting out of the end of the pushrod. I have also modified a valve cover buy cutting a 1" wide slot the length of the cover so you can access the adjustment nut with the cover installed.
Without any attempt to slow oil flow, warm the engine up first, this will lower oil pressure at idle. With valve cover removed, expect to lose a quart of oil, running down the engine block, exhaust, ect... on to the floor. Depending on how fast you are adjusting. Basically back off the nut until it clicks loudly, then tighten until it stops, and go 1/4 to 1/2 turn. Given your scenario, it may stop ticking for a couple cycles then become noisey again. I suppose you could tighten all the lifter plunger movement out so the 'bad' lifter can't bleed down, but you run the risk of a valve not closing. This would be a very fine line to adjust to. Others may have more suggestions, but that's all I got.
Keep us up-dated as to what you find.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
Well,it seems that he's checked about everything else.His comments about the markings on the valve stem tip sounds like a valve moving around.
 

MRHP

 
Supporting Member 1
Have you verified the firing order? An exhaust leak at the manifold can make a tick noise. Was the cam a 4/7 swap cam? Pull one plug wire at a time while engine is running and try to identify what cylinder or cylinders are not firing properly. Pull plugs and inspect for proper gap and look at the color or wetness of them. Just thinking out loud. Use thermostat gun on exhaust manifold to find a weak cylinder.
 

oldrod40

Active Member
Supporting Member 1
I know its hard to try and guess whats happening when your not in front of it and I could be missing something easy thats happening that any of you could see and tell me exactly what is going on. All the suggestions are great and are knowledge to hold on to. The heads I put on were at a machine shop and redone-milled, valve job, new guides, valves, springs, magna fluxed etc. So I would hope all that was done correctly but I know there is always the chance it wasnt. This engine only has 900 miles on it since a rebuild. I did try doing some adjusting with the covers off, don't know if there is a special tool but my socket would make some contact with the rocker and I didnt want to mess anything more up so I only adjusted a couple but no difference that I noticed. I went back over all the timing, threw the timing light on all cylinders to make sure spark was getting to all the plugs. Didnt think about the thermostat gun, but listening to it with the valve covers off it differently sounds like I have two lifters on each side that are making the noise.

At this point I'm going to go ahead and pull the intake and see what I got inside. I guess there is a chance when I first adjusted and had issues with the first set of springs I could have over tightened trying to get rid of the noise. I do have a couple lifter questions you all will probably know.

I bought the Isky lifters when I bought the cam, if I remember right I bought the hi performance ones from show cars, are these anti-pump lifters?

When I pull the lifters is there a way to tell if they are collapsed? I know they have a springs and new you can depress them. Figured if they set enough oil will drain and I can check if they move. I will inspect them for abnormal wear in case that happened.

If I find one or a couple bad lifters with the low miles on the engine can I buy a couple and replace or is it best to replace the cam with new lifters? I was looking a little and I didn't see any Isky lifters sold in singles, guessing that is their way of saying dont just replace one? But I also dont want to replace a set of lifters and end up replacing cam and lifters a short time down the road. Guess it sounds like I am answering my own question on this last one.

Thanks again for all the advice, I'll let you know what happens. Lots of snow here and getting more this weekend, sounds like great garage weather!
 

Don Jacks

Well Seasoned Member
Supporting Member 3
No longer han you ran it,it likely won't hurt to put lifters on it SO LONG AS YOU RECOAT THE CAM AND LIFTERS with break in lube.Pull the intake first and look closely at the push rods and how far down the lifter plungers are sitting with the valve train in place. Make sure that none of the push rods are bent
 

Jeffrey Osstyn

Well Known Member
Supporting Member 3
After doing the valve train check with the marking ink.
Your statement about 'two contact points' is something to re-visit. You are using stock rockers, are they used? Even if new they could be a problem. You may want to check the contact pad on the rocker to see if they are flat. Used rockers in the past were re-surfaced with a grinder to make them flat again. These days the 'new' replacements are always suspect and need a good look over. Personally I go with the full roller rockers these days. You get more precise rocker ratios and I am not a fan of the stock 'sliding' action over the valve stem tip from the stockers. But they did work for years when these were new, personal preference I guess.
Your issue with your socket adjusting the rocker nut while running is common, use a thin wall socket or grind yours down on the O.D. That should fix the un-wanted contact with the moving rocker arm.
 

Don Jacks

Well Seasoned Member
Supporting Member 3
"Suspect" is putting it mildly when dealing with new stock replacement rockers.Jeffery's right,go with either a roller tip or full roller style rocker arm,you'll sleep better.
 

oldrod40

Active Member
Supporting Member 1
So i probably did something I should have wanted for but I bought new lifters put them in and no change......so not a lifter problem!
I only fired it up to break in the new lifters and forgot to hit it with the thermometer gun on the headers but I will next time I start it to see if there is a temperature change. I did go back to examine the valve rocker contact. I attached pics. I also used a bore scope to look in the cylinders. All of them look wet, all but two of my plugs are black and the two that arent are close. Looking in the cylinders I notice valve impressions on the #1 5 6 8 pistons. All look on the intake side. I used a cometic .027 thick gasket. I know there needs to be measurements taken but from what I found my pistons were in the hole .020 to .025 which would make for the quench and what I thought would be clearance for the Isky 0921 cam. Guess these heads could have been milled more then what I thought??. I did turn the motor over by hand prior to start up and had no valve to piston contact or bind. Cranking the motor I don't hear any contact but light contact could be missed. Maybe the timing chain jumped and advanced the cam? I feel like with the wet cylinders and plugs I'm getting too much fuel but I dont think that would cause a ticking plus the valve impressions. Looking at the valve-rockers marks(I'm novice here) looks like the 2 intake 4 exhaust 6 intake are not proper. I'm using the factor length pushrods and none are bent. As far as my rockers, they are the stock original. They came with the engine when I bought it probably around 8 years ago.

I guess a bad job on the heads with guides could cause the valves to stick but there were rebuilt with all new parts as far as I can tell, prior to assembly I took a look and the valves, guides, retainers etc all look new. If for some reason the head gasket is causing the clearance issue does all the other symptoms match up? I know taking this somewhere is probably the best choice, and have someone who knows a lot more than me could probably figure it out quick. I do get joy in finding the problem and solving it, building this is my stress relief but definitely can cause a little. If anyone has someone in the St. Louis are as suggestion I'll take it, but I'm not done trying myself yet.

The only things changed in this head swap was the head gaskets (and the others when changing them out) new spark plugs and now new lifters. Again thanks for all the suggestions!
 

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Don Jacks

Well Seasoned Member
Supporting Member 3
I'd suggest pulling the timing chain cover and to check the timing chain and gears.Crank and cam gears can,and have been installed using the wrong
"dots".The result is what you're dealing with,,,,,,,,,bent valves.
 
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