Valve Tip/Rocker Height Question??

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Treblig

Treblig

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I've read a lot about Mopar small block valves tips needing to be the same height after assembly. Does it does it really matter if they are the same height if you use adjustable rockers?? I recently (one year ago) had a set of 302 castings completely redone at the machine shop and installed them on my stock 318. I wasn't a FABO member so I didn't know anything about the valve heights so I never bothered to ask the machinist nor did I check the heads after overhaul. I'm not even sure if I put the rockers on correctly. But the car runs pretty good although I thought I would get a little more power out of the mildly ported 302s. The engine currently has non adjustable rockers on the original '69 motor. I bought a set of adjustable rockers and I'm wondering it would help if I swapped out the rockers since the valves may not all be the same height??? I bought the adjustable rockers for the 318/390 stroker I plan to build but until I finish the 390 I wanted to see if I could improve the 318 for now. Will the adjustable rockers compensate for the valves NOT being the same height???

Treblig
 
Yes you'd be able to adjust the valves individually but the other issue with different heights is that the springs will be at different seat pressures unless corrected with shims. Not sure that's really an issue as long as you don't rev it to the moon.
 
No high revving for me.... 5800 and below. I do remember the machinist saying that he properly shimmed all the valves and had to cut the spring seats for the seals. He even told me the spring pressures but I don't remember what they were. But since I didn't know about the spring heights I didn't even ask. So your saying that IF the valve tips are not all the same height I could put the adjustable rockers on the heads and compensate for any difference in valve height?? If that's the case then it really doesn't matter that much about the valve tip height unless your using non adjustable rockers?? When I do the 390 I was planning on using 360 heads but on these heads I do plan on letting the machinist know about the valve tip heights even though it shouldn't make a difference with the adjustable rockers.


thanks,
Treblig
 
Treblig said:
Will the adjustable rockers compensate for the valves NOT being the same height???

Treblig
Click to expand...

Short answer, NO. They are all mounted on a shaft that is bolted to the head. You can NOT adjust the roller tip to valve tip individually from rocker to rocker like a Stud mount rocker(like a SBC or Magnum). That is why it is VERY CRITICAL that all your valve tips on a Mopar are within .010-.020" of each other to insure the rocker geometry is correct.
 
MLR Performance,

I am not using roller rockers. It's a stock type set up except for the Mopar ductile iron adjustable rockers. But I do think I understand what you are saying. If the height of the PIVOT point of the rocker doesn't change then the adjustable rockers won't compensate, CORRECT??? Then I guess the only reason to use adj rockers is to be able to adjust the valve tip to rocker contact (scrub)??? I'm asking all these questions so I can build my next engine and NOT make the same mistakes I made when I put the 302 castings on my 318 and to replace the stock rockers with adjustable rockers hoping it will make my current engine run better. If the adj rockers won't help then I'll just leave the stock (non adj) rockers on the 318 until I get the 390 built.

Treblig
 
I do not believe your lifter preload will be equal with the stock rockers which would be of more concern than scrub. That said, I doubt you'd notice any difference in performance with adjustable rockers. I say save for the new build.
 
Treblig said:
Then I guess the only reason to use adj rockers is to be able to adjust the valve tip to rocker contact (scrub)???
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No. The pushrod Can Not change the rocker tip to valve stem tip contact. The rockers are Fixed and can not move around. Adjustable rockers will allow you to set lash and adjust pre-load(hyd). They also allow to to adjust the pushrod pivot vs the rocker pivot center-line, this affects over all lift/duration and scrub to a point, but it does Nothing for the actual contact of the rocker tip to valve stem tip contact point. The only way to do that is to physically move the rocker shaft up, down or toward or away from the valves. Or change the valve stem heights.

Here is an example
If your rocker tip is to far to the inside of the engine, or intake side, changing the pushrod length will not do anything. You either have to move the shaft up or use shorter valves.

Does this make sense now??? I know sometimes its hard to wrap you brain around stuff like this unless you have it right in front of you and can see it working.
 
So valve tip length is critical no matter what type of rocker you use...CORRECT??/ If you set the valve to the correct height then you won't have any problem with scrub (especially if you have adj rockers), RIGHT?? Now I think I understand...the distance from the rocker PIVOT point (to the valve) will never change so the tip of the valve has to be very close to the correct height to keep the relationship between the valve and the rocker correct...is that right??/ So you set the valve to the correct height (by the book) and you get the correct "scrub" by getting the correct push rod length and adjusting the rockers for correct valve lash (hyd). The only way to correct scrub discrepancies is to change the valve height (or maybe shim the rocker shaft)??

treblig
 
FWIW, you should also realize that if the valve tips are at different heights, that means some valves have been "sunk" through the valve job and won't flow equally, and chamber cc's will be different as well, varying compression. Of course, I'm splitting hairs. It just depends how "right" you want your heads to be. Hopefully at least the spring installed heights were individually measured and adjusted.
 
yes I remember the machinist telling me that the springs were all the correct height (302 castings) and pressure (All new valves). But I didn't ask about valve height (as opposed to spring height). My original question was "if adj rockers could compensate for the valves not being the same height". I think that question has been answered...NO!! But also the valve length (height) has to be correct so that the relationship between the rocker PIVOT point and the valve tip stays correct. When I get the 360 heads machined (all new valves) I'll know what to ask and make sure I get what I ask for. Not only do the valves have to be the correct height but they also must be very close to each other (within .010-.020). Is all this correct on my part??

Treblig
 
Yup, you got it. And if you have to sink the valve to far, it time to get new seat/valves to make it right. These some of the little things that make a good engine great, and why having a shop that knows how to fix this crap is so important. Chevy stuff is different, and most Chevy shops dont have a clue on Mopar stuff.

I will post some pics of a set of heads we got in here a while ago, stems heights were all over the place. The machine shop he had them done at just said "Use a different pushrod", that dont work on shaft mount rockers. Cost him twice to get it right, thats a shame.
 
why are you worrying about valve stem heights ?because you believe your power is being robbed ? all you did was replace the cylinders head with a 302 casting unless the valves were burned with major missing. switching the head design on a old tired 1969/318 ,is it still a 2 barrel stock cam engine? you would only see 15 hp difference .
 
Thanks MRL,.

Teringer, I not complaining that loud. My 318 is a '69 which was overhauled before I bought it and had a mild cam installed. I measured the piston height when I replaced the heads, it had .039 gap at TDC. That means it's one if the higher compression motors. I wanted to go with better exhaust so I found a 340 driver's side exhaust manifold and also bought a passenger's side Mag truck 360 manifold. I already had 2 1/2 exhaust all the way back (with cross over). When I had the sealing problem with the mag truck manifold (the ports are much larger) I decide to go with the 302 castings to get a good seal. I ported the 302s and installed new SS valves. The engine already had a 600 Edelbrock and performer intake. So with the 302 closed chamber "ported" heads and improved exhaust manifolds I expected a good 20-30 HP increase. It runs well but still doesn't have the torque and power I'm looking for (3.08 gears). Maybe I'm asking too much. I'm in the process of installing a 2004R transmission into my Cuda (and switching to 4.10 gears) so that should help on the low end. It's just that now that I done all this reading at the FABO web site I realized that I never checked the valve height nor whether they were close to the same height. I bought a nice set of adj rockers for the 390 I plan to build and was wondering if the rockers might help since I never checked to make sure the 302 casting valves were all the same height. I guess I should have mentioned the mild cam in my first post but the question was strictly about using adj rockers to compensate for varying valve heights.

treblig
 
The 318 just doesn't have any torque to begin with, so you need gearing to get the car rolling. The 4:10s & overdrive trans will be a nice package, IMO.
 
sorry if I came on too strong, but dealing with the general public some times people think just because they paid hundreds of dollars for a tune up they should get a extra 50 hp/plus 100 mpg. in by experience the stock 360 cam is one of the best cams for the 318 with stock gearing. most people want a big hemi grind , but with the thick head gasket and the piston down in the hole your still near 8.5 to 1 comp. and just a mild performance cam is too much. the one I'm talking about is .424 lift .good luck and yes I over camed everything in by youth listing to experts.
 
I had no idea that a stock 360 cam worked well in a 318!!! But in my case, I'm going to build a 318/390 stroker so I don't see a need to put a 360 cam in my 318 using money that I could use on the stroker build. But just in case I don't build the 390....what year 360 cam would were you talking about??? I believe my '69 318 has 9.2 to 1 compression ratio ('69 Service Manual)

PS- unless someone attacks me personally I don't take offense!!! you just didn't know all the specs on my engine.


treblig
 
the 1970/73 cam is great with good bottom end torque , and most want the 340 stock cam but that ran with 10.5 comp, this is why it didn't run as well in the low comp 340. It wasn't the small intake valve everyone complains about .
 
teringer said:
the 1970/73 cam is great with good bottom end torque , and most want the 340 stock cam but that ran with 10.5 comp, this is why it didn't run as well in the low comp 340. It wasn't the small intake valve everyone complains about .
Click to expand...


OK, Thanks Teringer,

treblig
 
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