Lenght of the shaft on intake valve?

[Zwap]

Hi,

I got my hands on a pair of rebuilt 915 heads a couple of mounth ago.
Now when I was planning to mount them I see that the shaft on the intake valve is a tiny bit shorter than the exhaust valave, if I look at the cylinderhead in its lenght I see everey intake valveshaft a little bit lower than the exhaust valveshaft, about 0.03 lower.
I think they'd use a different brand of intake and exhase valves.
Is it possible to use stock lifters, pushrods and rocker arms? Or do I have to use adjustable pushrods on either exhaust or intake?
It's a bone stock 383 4bbl.

 

[65sporty]

I would take them to a machine shop you trust and have them check the installed height of the valves to make sure they are in spec, if so you can run the factory set up

 

[Big_John]

Since it sounds like these heads are already assembled, you can write off .030" in height difference pretty easy. It's not unusual to grind the end of a used valve a bit to clean it up. Other issues are how much material was removed from both the valve seats and the valve faces. If they installed hardened valve seats, there can also be some accumulated differences.

It's very likely that they replaced the exhaust valves and reworked the intakes. That's quite often the way it is done.

Do you know what was done to these heads in the rebuilding process? Some people's definition of "rebuilt" is way different from others.

Your hydraulic lifters are built to make up for small differences like this. As long as they aren't topped out, you can use the stock valve train without a worry.

 

[Big_John]

I would take them to a machine shop you trust and have them check the installed height of the valves to make sure they are in spec, if so you can run the factory set up

This is a really good idea.... In fact, I would have them look over everything. Buying rebuilt is good as long as the rebuilder is competent and all the bases were covered in the process.

 

[Yatzee]

Hi,

I got my hands on a pair of rebuilt 915 heads a couple of mounth ago.
Now when I was planning to mount them I see that the shaft on the intake valve is a tiny bit shorter than the exhaust valave, if I look at the cylinderhead in its lenght I see everey intake valveshaft a little bit lower than the exhaust valveshaft, about 0.03 lower.
I think they'd use a different brand of intake and exhase valves.
Is it possible to use stock lifters, pushrods and rocker arms? Or do I have to use adjustable pushrods on either exhaust or intake?
It's a bone stock 383 4bbl.

Keep in mind that the stems on exhaust valves expand as they heat up. 3 thousands is nothing. Warm the engine and measure again - I bet the expansion is built into the stems by the manufacturer.

 

[Zwap]

They are assembled but not mounted so I cant warm up the engine to measure them, but I did a little more exactly measure yesterday and every intake valve shaft is 0.020 down lower than the exhaust valve shaft.

Another thing is if you think I should use the original Mopar steel shim cylinder head gasket to keep CR or should I use a composition head gasket to get a better sealant?

 

[Big_John]

Use the composition gasket. Best way to go.

 

[Big_John]

Keep in mind that the stems on exhaust valves expand as they heat up. 3 thousands is nothing. Warm the engine and measure again - I bet the expansion is built into the stems by the manufacturer.

True, but the measurement he first took was .03" or expressed as commonly as 30 thousandths. 10 times more. It's usually written as .030" in machine shops.

You are quite correct that .003" is nothing, .030" is a lot.

 

[Zwap]

.020" is less, do you still think I shuold grind off the exhaust shaft i bit?

Use the composition gasket. Best way to go.

I belive you, but why?

 

[Big_John]

.020" is less, do you still think I shuold grind off the exhaust shaft i bit?



I belive you, but why?

No, do not grind off the valve stem! You are worrying over nothing.

Edit: after reading my above post, I want to be sure you understand that I did not recommend grinding your valve stem. As part of the rebuild, it's common practice to grind the top of the valve stem with a used valve. This is done to fix any wear to the end of the valve stem from the rocker arm. It's done with the valve out and is just part of reworking a used valve.

If you really feel something is wrong, follow the advice given above and have a GOOD machine shop check the heads over.

The composition gasket will seal better and there's no need to retorque the heads after running it. Some guys don't retorque the steel gasket, but I always have. It's a PITA with a 440 because the exhaust manifolds and rocker shafts have to come back off.

The loss in compression is minimal and you will never feel any difference.

 

[Big_John]

To illustrate how the valve is reconditioned. Here's a pretty good video I found. At the 2:00 minute mark, he refaces the end of the valve. This is typical shop practice.

 

[70bigblockdodge]

The lifters compensate for in some cases up to .120, so a small amount is nothing to worry about even with solid lifters the adjusters in the rocker arms. The geometry will not be effected with this small amount with near stock lifts, of you were opening the valve to like .800 then the extra .020 make make a difference. I would not sweat it but if you don't feel comfortable with the rebuild in you eye it might pay to have a shop you can trust look at them, as mentioned above.

 

[Zwap]

Well, I don't have a shop nearby that handle iron cast cylinder heads that much that I really trust so I have to trust yours and my own experience.
I feel confortable about the rebuild, the heads was running about one year after the rebuild but the owner decides to put on aluminium heads instead for different reasons, but I never asked him what valve train he was running.
I understand and agree about the reason to get composition gasket but I don't think steel chim gaskets needs to retorque more than maybe once because steel don't compress due to temperature or movement that much as composition gaskets do, but for sealens there's a point to use composition gasket as they are more forgiven to uneven surface.
I might get the head milled just one thousand or two just to get a solid straight surface to use steel shim gasket, or a little bit more to use composition to keep the already "low" CR. I think in the real wold it's more like 8.5:1 with the original 0.020 steel shim gasket no matter what the specification from Chrysler says, and I don't want to get much lower than that, with a FelPro 0.040 gasket I would end up with a CR near 8.0:1 I think.

 

[max1196]

The intake valve tip being at a lesser height by laying a straight edge across all the tips suggests to me that the exhaust valves may be receding due to the fact there may have not been hardened exhaust valve seats installed during the "rebuild". Do consider the suggestions above and have a shop check them out!

 

[70bigblockdodge]

You will be lucky to gain .2 of a compression point with the steel head gasket on a 383 with its small bore over a composition gasket. What year engine is this if it is a 70 4 bbl engine and you swap 915 closed chambers on it in place of the original 906 opens you might want to stack a couple of composition gaskets.

 

[moper]

If it were me I would have the heads fixed. .030" of stem difference is a problem. It's not the slop in the valvetrain, but the geometry of the rockers that are a problem. If the exh is taller, the exh valves were sunk during the rebuild, and they couldn't dress enough off the end of the stem to compensate for it withotu really cutting through the hardened layer. The heads should have gotten new (unleaded) seats and new exhaust valves. Someone cheaped out and the result is a problem as far as I'm concerned. Running doesn't consitute a performance engine, and rocker geometry is a huge part of real performance and longevity. Shims are not the fix, nor are longer pushrods.
I would run the steel shim. Properly prepped and installed you don't have to retorque them and anything on a 383 will only help.

 

[Big_John]

.030" of stem difference is a problem. It's not the slop in the valvetrain, but the geometry of the rockers that are a problem.

The geometry of the stock, stamped steel rocker arms is pretty forgiving. If you think about it, many people add .100 in valve lift and use the stock rockers and never give it a thought. They also may cut .030" or more off the heads and/or deck without ill effects.

It doesn't mean that that is the right thing to do with a race engine or even a really good street engine. IMHO, one of the first things tossed over your shoulder for an engine like that is the rocker arms. In this case, the OP is just putting some used heads on a car.

 

[heyoldguy]

If it were me I would have the heads fixed. .030" of stem difference is a problem. It's not the slop in the valvetrain, but the geometry of the rockers that are a problem. If the exh is taller, the exh valves were sunk during the rebuild, and they couldn't dress enough off the end of the stem to compensate for it withotu really cutting through the hardened layer. The heads should have gotten new (unleaded) seats and new exhaust valves. Someone cheaped out and the result is a problem as far as I'm concerned. Running doesn't consitute a performance engine, and rocker geometry is a huge part of real performance and longevity. Shims are not the fix, nor are longer pushrods.
I would run the steel shim. Properly prepped and installed you don't have to retorque them and anything on a 383 will only help.

This is a losing battle moper, these guys are even patting themselves on the back for coming up with the idea of stacking composition head gaskets...........run for the hills!

 

[Zwap]

"heyoldguy", the engine is a 1966 383 stock 4-bbl and I'm replacing my old 516 heads (that have been used on a couple of engines) with used but rebuid 915 heads, the rest is described if you read the whole thread:
About 0.020 intake valve lower on EVERY valve shaft than the exhaust valve shaft.
No nearby shop that I feel confortable with.
Is it possible to use new but stock valvetrain?
Should I use steel shim headgasket to keep CR or go for composition to get better sealant?

Does a difference in 0.020 really does that much differnce in perfomance in matter of geometry of the rockers, then I would't use this 915 heads, I think I better get the 516 rebuid as they have exactly the same height in valve shaft, even if they have passed a couple of engines and a LOTS of unlead fuel the past 15 years, no sunk here but they slip a bit of oil by the guides.

"Someone cheaped out" about the harden seats is one that I didn't think of but I don't think so as the rest of the car that the heads came from was a fairly expensive car, the owner just want more power with a stroker kit and alu heads and these 915 heads was left-over, but maybe your right.
If there would be a sunk because of unlead gas, would it be about the same on every exhaust valve?
Every valve shaft has a difference in height about exactly 0.020

I think, but thats only what I think, thats there is a reason why the rebuilder build it this way, but I don't know why and I would to hear (read) as many possible reason as possible.

I've got a lots of good sugesstions but "heyoldguy", whats your opinion?
"Lose the battle" and "Run for the hills"?

 

[heyoldguy]

Does it still have the stock 1966 lifters and pushrods? I ask because the 1966 engines were supposed to have 1/4" balls on the pushrods that went into the 1/4" cups in the lifters. .020" doesn't seem like an insurmountable amount of difference for the hydraulic to overcome. I've seem many stock heads come off engines with more difference than that and they were still functioning fine. I would take one of the existing lifters out of the engine and slowly compress the center of the lifter and measure how much travel there is in the hydraulics of the lifter. Then you can measure the pushrod length with the new heads bolted on and see if you have the correct preload for the lifter. If the existing pushrods collapse the lifter about 1/2 way they would work for sure.

Swapping the 516 for the 915 heads and using the stock steel shim type heads gasket should work if the block and head surfaces are still flat.

Generally one or two exhaust valves will be much farther recessed in the combustion chamber and sticking up real high on the valve spring side if the valves are recessing because of the unleaded fuel. I agree that it is unlikely that all exhaust valves would recess exactly the same amount.

Why did the head builder leave them .020" different? I have no idea. We get all the tip heights to within a few thousandths on the cylinder heads we do, but if we don't do the block rebuild then sometime the customer finds that his block isn't decked to within .020" of square.

Do I have the slightest idea what I am talking about? In some peoples eyes probably not.

Pictures of the last iron heads we did........