Machining For Screw In Studs & Guide Plates - Push Rod Hole???

[BB1960]

Hi All,

The engine is getting a little fresh up with the heads coming off and replacing the cam, rockers, and valve train.

The only thing I'm not sure about having done it when using non-self aligning rockers (Scorpion), how much do you have to machine out the push rod slots in the head??? I will be running show-cars guide plates.

It's a low perf head with the 5/16 push rods.... I'll be dropping the heads off at the machine shop and want to make sure there is engouh clearance for a cam with 268 degree on the intake with .525 life and 280 on the exhaust with .535 lift.....

 

[models916]

.375 is what I have.

 

[BB1960]

How much lift/duration are you running with 3/8 holes?

 

[Ronnie Russell]

5/16 pushrods, #817 heads, stock untouched pushrod holes, 546/536 lift. No contact after 4 years. Do you really need guide plates?

 

[Ishiftem]

With 3/8 pushrods we run over 650 lift and in excess of 250 duration @ .050 with the stock pushrod holes in 690 heads.. I would want guide plates if I were using full roller rocker with 5/16 pushrods.

 

[BB1960]

With 3/8 pushrods we run over 650 lift and in excess of 250 duration @ .050 with the stock pushrod holes in 690 heads.. I would want guide plates if I were using full roller rocker with 5/16 pushrods.

I am using full roller rockers with 5/16 pushrods. I'm worried about pushrod bind with the stock slots, hence the guideplates......... I've got the heads off, I really should've done this when I originally got the engine built. I dont want to have to go back a 3rd time...........

5/16 pushrods, #817 heads, stock untouched pushrod holes, 546/536 lift. No contact after 4 years. Do you really need guide plates?

Not 100% sure that I need them, but just like a condom, you'd rather have it and not need it, than need it an not have it!!!! I'm hoping this is the last time for a while I have to disassemble the engine..... I'd rather just do it....Besides, I've already bought the guide plates and still need to get the stud bosses machined, I might as well do it........

Based on what you've both said, 3/8 should be fine.

Thanks gents.

 

[boxerdog]

I guess I am just used to SBC's, but I have enlarged the pushrod holes and used Showcars guide plates on all of my W motors, even with 3/8" pushrods. Nothing over .600 lift so far, but they seem to work very well.

 

[BB1960]

I guess I am just used to SBC's, but I have enlarged the pushrod holes and used Showcars guide plates on all of my W motors, even with 3/8" pushrods. Nothing over .600 lift so far, but they seem to work very well.

What diameter did you enlarge them to?

 

[boxerdog]

It's been a while, but I am pretty sure it was 7/16" on the 3/8 pushrod motors...just enough to make sure that the pushrod is only "guided" by the plate. Likewise, the one 5/16 pushrod motor I did was enlarged to 3/8".

 

[CDNpontiac409guy]

Enlarging pushrod guide holes in W block heads ?
HHMMM.
Never did it.
Never would do it.
Besides being another one of those redundant, unnecessary "up-sell features" ( such as surfacing the bellhousing mating surface of a block ) of race engine shops... it compromises a VERY thin area of the "pinch" in the intake runner, reducing the potential for effective porting ( and yes, if you have guide lates... those heads better have alrady been ported ).
Ronnie described a perfect axample of how unecesary it is.

 

[Don Jacks]

Thanks Aubrey,and Ronnie,you just explained what I was wondering about for my build,and as a result saved me some money.

 

[boxerdog]

My situation wasn't one of upsell at all, it's a 30-minute job, but you might be right about the procedure compromising porting. I had no intention of grinding away on my 583's but I have pretty good recollections of W owners including myself having spare pushrods in the glove box. It seems like production tolerances might have been a little loose. Using the plates allows one to center the rocker on the valve stem if needed, pretty common on SBCs, which actually have simpler rocker arm geometry than Ws. JMO

 

[Ronnie Russell]

sbc have simpler geometry than Ws ???? Dave, you sure got that right !!!! Ws do have lousy geometry but the problems I have seen is that too many people switch to roller rockers and don't take pushrod length seriously. The stamped steel rockers are more forgiving because of the contact pad on the rocker. I know you are not in that group because I know of your experience, just saying it is a problem for many. I haven't run into 690s are 583s that need guide plates to correct a problem. Come to think of it, I haven't had problems with the 333s or 817s either. That don't mean the next set will be good. I hope you don't think I was raggin' on guide plates. Guide plates are good, if needed. Every aftermarket head I can think of come with them out of the box. We all want to build whats best. My point was a chrome moly, .080 wall 5/16 pushrod is sufficient for almost anything except race only application. I did drill some 333s and use guide plates with 3/8 pushrods because I intended to build a low budget race only engine to compete with Tom K a couple of years ago but the project changed and the heads went on the street and never see any rpms. Also, I would never argue that 3/8 arent stronger than 5/16. The 3/8 are much much stronger. But how strong is strong enough? Most people will err on the side of strength and change to 3/8. I don't have a problem with that. I'm just an old fart and believe in the old adage, " if it ain't broke, don't fix it ". And like I said, I haven't run into any GM iron heads that need guide plates. No doubt , I have been lucky.

 

[LMBRJQ 60]

Ronnie, Dave
just on this my 348 has 1147 heads and the valve train is all original only cleaned up. was looking at running as is and then scavenging parts for a 348/421 stroker 396 crank etc. Was going to go screw in studs and scorpion roller rockers in this case i would have to check the rocker geometry as a given but is there a need for guide plates in this case or is it a case by case thing depending on the castings?
Was looking at doing the heads etc now if needed then only have a rotating assembly to re install??? later
Steve

 

[boxerdog]

Ronnie, you are right on as usual. As you mentioned, the other important variables are pushrod length and 100 different brands of roller rockers! Some of them Chinese.....but that's another subject entirely. I have one running with Comp Magnum street rockers just because I liked keeping the ball mount for a hydraulic lifter cruiser motor.

If we built them all the same, they'd be boring! I haven't run this last one much past 7200, but so far so good. It has Crane BBC rockers and guide plates. Think I'll go run the valves and see how it's holding up!

 

[boxerdog]

Steve, I'd mock it up and check it out, but I would sure do the studs, and I have heard that the Scorpion rockers are pretty good. I just didn't want to do an extra dry run and then have to re-cut the heads for guide plates.

However, a lot of these guys don't have valve train problems and have done more Ws than I have, so maybe next time I won't be so quick to chop away. In the end, it's your call!

 

[Ronnie Russell]

Steve, Your question is much more complicated than one might think. If you were using 817s or 333s, I would suggest cutting the bosses .400 , that would give you the option of guide plates or no guide plates. Studs are available in almost any length. Its all about the correct shank length. Easy to mock up and decide. But,,,, I hate cutting on a rare head like the 1147. Like Dave said, in the end, it's your call. Tough decision. Dave, I didn't even think of the Chinese rockers. That is a major issue for anyone thinking of trying to save money. Im all for saving money but you can't do it with Chinese rockers. Destruction guaranteed. I do like the Scorpions. Got em on mine. But the Comp Pro Magnums go on the other builds.

 

[BB1960]

Enlarging pushrod guide holes in W block heads ?
HHMMM.
Never did it.
Never would do it.
Besides being another one of those redundant, unnecessary "up-sell features" ( such as surfacing the bellhousing mating surface of a block ) of race engine shops... it compromises a VERY thin area of the "pinch" in the intake runner, reducing the potential for effective porting ( and yes, if you have guide lates... those heads better have alrady been ported ).
Ronnie described a perfect axample of how unecesary it is.

The heads have not been ported, it is supercharged though. If I was going to get them ported I would just buy some Edelbrocks and be done with it. But for the extra $2500 (heads and manfolds) I cant justify it. For the power I want to make I dont think the porting is necessary.... It is for street motor aiming for about 450-500hp that wont rev past 5500rpm

 

[models916]

mid 5 cams with 333 heads and 5/16 pushrods will need the hole slotted a little. Just add a rat tail file to a drill and open so it doesn't touch.

 

[Ronnie Russell]

Just talked to my machinist about the cut on stud bosses. He says he cuts .375 . He said this allows guide plates or no guide plates. .400 is okay but no reason to cut more than neccessary.