Patrick03

I have a set of Pro-Filer heads I'm putting on top of a block I'm building out to be a 383. The block has been zero decked and I'm using a .039" head gasket. The pushrod length I'm coming up with is 8.25" long. I'm scratching my head trying to figure out how I'm coming up with something .45" longer than stock. Are the heads different enough that the valve sits .45" higher than in stock heads? I called Pro-Filer and they confirmed the valves are stock length and said they weren't surprised by the longer pushrod. They didn't know how much longer it should be, just that it wasn't surprising that it was longer. I'm using stock height solid lifters and an LT1 cam. Just curious if others have had similar findings.

To determine pushrod length, I used an adjustable length pushrod, marked the tip of the valve stem with magic marker, and rotated the engine to get two full valve open/close cycles. See pics below. The first one is with the 8.25" pushrod and the secone one is with a stock length (7.8") pushrod.




8.25" pushrod




7.8" pushrod


Thanks,
Patrick

427Hotrod

You're looking for minimum sweep which is more important than being dead center. There's a lot of variables that add up to get geometry correct.

Here's a video that shows the "mid-lift" version of things.

https://www.youtube.com/watch?v=o5is...ature=youtu.be



JIM

Robert61

Being a 383 you may have a small base circle cam for rod clearance that would cause the need for at least a +.100 push rod. And then variances in the head might call for more. Your pattern with the 8.25 looks good.

GCD1962

Edelbrock heads call for +.100 pushrods with their ALum heads.

GearheadJoe

While a small base circle cam would seem likely to require a longer pushrod, the OP is using a stock LT1 cam, not a cam with a small base circle.

I'm very surprised at the big increase (.45") in pushrod length, but it's hard to argue with the very nice contact pattern that he is getting. I just can't figure out why the difference in pushrod length is so large.

Patrick03

Thanks for the input guys. Like Joe said, I don't have a small base circle cam, but that was a good thought.

I watched the video Jim posted and that method of determining pushrod length makes sense. Much easier to find the center of rotation with a full roller rocker than with a stamped roller like I have though. To find the center of rotation about the rocker stud, I placed a small cylindrical magnet on the rocker and then rocked it back and forth and moved the magnet around till it seemed to be in the center. Maybe the pic below will be of help. If anyone has another suggestion, let me know. Google wasn't very helpful this time. Didn't get further than this tonight.

Also, I found one source that said the witness mark should be in the third closest to the intake, not in the center of the valve stem. Lots of conflicting info it there in determining the correct pushrod length. The video Jim posted though, made a lot of sense.

Moved rocker back and forth while holding stud in vice.

I think this is the center of rotation about the rocker stud
Line drawn between centers of rotation.

GearheadJoe

Hi Patrick:

I agree that there are a lot of conflicting opinions on the internet about where the contact pattern should be centered.

I subscribe to the theory that whenever the contact point is off-center on the valve tip, a lateral force will be exerted on the valve guide, accelerating wear. This force will be greater for larger offsets, and also greater for higher spring pressures.

According to this theory, the biggest lateral force will likely occur if the contact is off center at maximum lift.

When I set up the contact pattern on my engine, the contact pattern was a bit wider than yours, so I got to choose whether to center the pattern or bias it to one side or the other. I decided to arrange it so that the contact was exactly centered at maximum lift. That turned out to involve a small amount of offset from center for the overall pattern.

In your case, though, the contact pattern is so skinny that there is no need to think about where the contact is at maximum lift. I can't see why anyone would suggest that you put the contact pattern anywhere but where you show it. Visually, it looks perfect to me, but I just can't figure out the reason for the large .45" increase in pushrod length that it took to get that pattern.

Patrick03

So I tried out the 90* mid-lift method and came up with a pushrod length of 8-3/16", just 1/16" shy of the witness mark method. The good news is that a slightly shorter pushrod should give a witness mark close to center and on the intake side of the valve stem. What I still don't understand, is why is this pushrod so long??? Has anyone else with aftermarket aluminum heads ended up with pushrods this long?

cardo0

Wow! Thats nearly a 1/2" longer. I think you need to step back for the 100 foot veiw of whats happening Patrick. I see a couple of things that maybe contributing to longer than expected p-rod length.

Your centerline through the rocker roller fulcrum instead of the area of touch on the roller tip moves the p-rod end higher to get the desired 90 degree relationship. Please dont get me started on St_ _ _ _ Technologies less than accurate information. Hey maybe you want the centerline of the roller tip at 90* and I dont really know if that makes a significance in the sweep or not - and not going to spend the time to figure it. But that ST video leaves the novice looking for a method to find the 50% lift point on the flank of the cam - just a totally error likely situation even for those with considerable experience. Aligning the 90* rocker at the wrong point on the cam flank can definitely make an error in either direction. I can't afford to get into trouble over someones popular advice but I expect I can rightfully warn others - we will see here.

I think I'm seeing single valve springs in your pix which would suggest a moderate performance camshaft. I that case if your less than something like 0.55" lift I would use a p-rod checking tool just for a look as they only cost like $15 at the most. This should be a check to see if your method is reasonably close. 0.45" sounds very significant and I understand your concern. My guess is the checking tool would tell you your less than 0.1" off. Manley and ProForm both have cheap checking tools and sometimes the local parts stores have them on the shelf. If you need instructions just post so.

Good luck and take your time here. Though IMHO close is good enough for valve tip pattern. As long as it stays away from the edge you shouldn't have harmful sideloading. It's the lifter pre-load that is crucial to saving your cam, lifters and really entire engine.

BTW I really dont know which side of valve tip centerline is better as I always try to center it. And that's good enough for the cams I use.

Patrick03

Thanks for the input cardo. Take a look at the pics in my first post. I'm getting a great witness mark with a 8.25" pushrod. Using the mid lift method I came up with 8.189". Fully agree these numbers sound way too long, but I'm not sure what I could be doing wrong.

Patrick

cardo0

That mark looks quite thin as not much of a "sweep". Is that "witness mark" the full sweep as the lobe moves from full closed to full open and back to full closed? If it is then I dont see much of problem with either size p-rod you use. But I'm surprised to see nearly 1/2" difference in p-rod length makes such a small difference in the mark location. And I cant explain it.

Robert61

If you could get ahold of a stock assembled head you could set up a height gage. Slide the original head with valves under your set up touching off on the highest point of the valve with the deck surface of the head laying on your flat surface. Then slide your new head with valves under it and compare the valve heights. If the ProFilers have raised ports that could explain it but they would have to be raised quite a bit. Even then the valves would be a lot longer than stock.

Patrick03

Ok, I think I've figured out what is going on. I have my original block with heads, so I have something to go back to for checking things out. First I measured the height of the valve stem to top of the block. The actual number is irrelevant, what is important is that I got the same value when I made the measurement on the old block. So, I'm pretty convinced the stem height is the same (within less than 1/16" I'd guess).



Measuring distance from top of block to top of stem.

Next I put a stock length pushrod in both the new and the old engine and used the same 1.5:1 roller tip rocker. See pics for results:




Old block and head. Nicely centered pattern with stock pushrod.




Offset pattern (very close to edge of stem) on new engine and heads with stock pushrod.

Next I tried to measure the distance between the stem and the rocker stud. This is a harder measurement to make and I tried a variety of methods. Each method though resulted in the new heads having the rocker stud about .040" to .070" further away from the valve stem than in the old engine. Guess what? If I measure the distance between the witness mark (using the stock length pushrod) on the new engine to the center of the valve stem, I get about .070". So what I'm thinking is that the rocker stud is indeed further away from the valve stem with the new heads. A longer pushrod will move the contact point closer to the center of the valve stem which is exactly what I've been seeing.

So now the question is, do I use longer pushrods or do I get higher ratio rocker arms that should let me use closer to stock pushrods? Or do I do something else?

I didn't want to confuse the issue here too much, so I didn't mention before why I'm being so paranoid (or thorough) here. This is my second attempt at getting this engine built. The first attempt resulted in a cam shaft with all of the lobes wiped off during break-in. There are a couple things that might have been done wrong with the first build, and I've addressed all of those. Pushrod length is last variable I'm trying to make sure is right. On the first build I had 1.6:1 non-roller tip rockers and pushrods were 8.050" (gave good middle of stem witness marks).

All input is welcome.

Thanks,
Patrick

65tripleblack

Patrick:

I read your PM and when I get a few minutes will tell you what length pushrods I used. Gearhead Joe referred you to me. There are a lot of factors affecting length needed and really the only way to measure is with a checking pushrod. My pistons are 12 thou out the hole, Pro Filer heads, and full roller valvetrain. If you use your LT1 flat tappet cam then any comparison goes out the window because roller tappets are different than flat tappets.

PS: I suggest non roller tipped rockers. They don't provide any benefit like full roller trunnion rockers do. On the downside they are heavier than plain stamped steel rockers so more inertial mass makes it harder to control the valves.

Patrick03

Thanks 65TripleBlack. Please read through this thread when you get a chance. The only reason I went with the roller tip was to make it easier to get a good witness mark. I agree they don't offer much benefit other than that. I've been using an adjustable length pushrod and have been getting some interesting results.

While our pushrod lengths will be different since you are full roller, I'm wondering if you noticed your pushrods being longer than what would normally be expected with your cam and lifters? That would help confirm my suspicion that the rocker studs are indeed mounted further away from the valve stems than on the stock heads.

Thanks,
Patrick

BD104X

Higher ratio rockers are for changing effective lift, not for changing geometry. Needing different pushrods with aftermarket heads is pretty common - It sounds like you have done your due diligence and measured correctly, now you need to put the longer pushrods in and move on.

cardo0

I see your giving this your best try. Just something I would consider is trying one of those p-rod checkers I mentioned. A modest cam like the LT1 is pretty much what they are designed for. The 90* degree method with an adjustable p-rod is very accurate for sure but can be error prone. With a 0.45" difference I would have to try one just for reference.

Good luck.

jerry gollnick

I would check witness marks on several valves both intake and exhaust. it is common for aftermarket heads to move the location of the valves or mounting studs to allow larger volume runners. I ran into this issue and had very strange side to side motion on some cylinders.

65tripleblack

Are your ProFilers 185cc? Hopefully no bigger than that with your "low lift/mild dynamic" LT1 cam.

There are a few factors at play here. You reported that you wiped first cam during break-in. That happens more often than we like to see.

1. So Patrick.............you mentioned using moly break in lube earlier. That's better than the red stuff you get in the cam package AFAIAC. A good coating of that on the lobes, bores and lifter ends is good prep.

2. Be sure your oil pump is primed until you see oil out every one of the 16 pushrods before firing.

3. Be sure that your float bowls are full and you see a pump shot out the nozzles ensuring a normal fuel supply.

4. Take all measures to make sure that your timing is very close to where it should be.

5. Check for spark at plugs by removing a plug, grounding threads to engine block in a DRY AREA, cranking and checking for spark.

5. If the engine doesn't fire within a second or three of cranking, then your chances of wiping a lobe or four increase dramatically as time goes by.

6. The standard valve springs used for ALL GM cams of the era were rated at 80# on the seats. I advise you to remove what you have and install a set of VS-677 springs from Sealed Power/TRW.

7. The VS-677 springs are likely smaller diameter than what you have installed currently. You will need to install spring locators to keep them centered in the pockets of your ProFiler heads. The locators are almost always hardened to prevent the springs from galling against them.

8. You are better off using standard stamped rockers with your cam. Roller tips won't gain you anything and WILL add inertial weight. This will make it harder to control the valve springs.

9. The only accurate way to determine the proper pushrod length is by using a checking pushrod. The witness mark should be dead center the valve stem between outboard and inboard edges.

Best of luck to you.

Westlotorn

The variables I have not seen considered in this post.
1. Are both engines at TDC on the compression stroke so both engines have fully closed valves. Sorry but something is off so start at the basics.
2. Are both Lifters the same height.
Not much else will give you the variation you are fighting if you already confirmed the Heads and the Rocker arm towers sit at the same height.