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I tried searching and now a little confused. I bought and installed a set of summits sum-152123 heads on my small block along with summit roller tip rockers sum- 141706PL with poly locks. The rockers are non-aligning. Do I need 1 self-aligning rockers or 2 guide plates or 3 nothing. The heads have the small slot holes for the pushrod. I'll try to post sum pics.
With small slots in stock heads you don’t normally need guide plates. I have not seen after market heads with the small slots.
The main thing is make sure with guide plates or heads with small slots you use hardened push rods.
These heads must have come with instructions didn't they?
A quick search on Summit shows:
These heads must have their rocker stud pad machined (milled down) if guide plates are installed.
The reason for that is, the guide plate is like a shim and raises the rocker stud. This in effect changes the push rod length because the stud is now higher, so the rocker arm is higher (the thickness of the guide plate material, 1/8" maybe?)
Summit also states these heads are for Flat Tappet Cams. You have roller lifters showing.
These heads only flow 165 CFM
These heads are 72 CC chamber (no compression increase)
You also paid $800 for heavy iron heads.
Your car. Your money. You sure you want these heads?
They sure look good, but no real advantage over stock.
I agree probably not optimum however I will point out port volume does not mean a set of heads won't flow much better than another set with the same port size.
But those heads are definitely not the best choice
The obround slots could be sized to keep the rocker arm tips aligned with the top of the valve stem where you do not need guide plates. The slots control the side to side alignment at the stem tips We can't tell from here if the slots and pushrods fit well enough to adequately control the side to side movement but it needs to be pretty close. If the pushrod slot fit is rather sloppy side to side, a "guided tip" rocker would be a better choice as long as you get zero binding at the slot.
Word of caution - if you are running a solid lifter flat tappet you can not use "guided tip" rockers as there is no way to measure the lash. Not an issue here if running a hydraulic flat tappet cam.
Guide plates would require machine work so no I would not go there unless you really want to go there.
The pushrods do not change length either with guide plates or without. The rocker arm geometry does not change. I just need to point out that GM did not change pushrod lengths when they went to add guide plates.
Aftermarket heads today come with enlongated pushrod holes so they cover those people that want to change rocker ratios that change the angle of the pushrod where it goes up into the head. If you raise the rocker stud abit putting guide plates on makes no difference the rocker arm will simply be slightly lower on the stud thats no problem theres plenty of thread length to cover that change and the factory never had to use different rocker stud lengths with or without guide plates, what effects length of pushrods is length of the valve taller valve springs. In those cases when you change to longer valves and longer pushrods then you need taller ( longer length ) aftermarket rocker studs. Get yourself some pushrod guide plates. If you look at your slots there both sloted and wider then an original heads round holes were, you need the guide plates up top.
Last edited by Little Mouse; Jun 1, 2023 at 11:46 AM.
You need guide plates.....I recommend the split ones.......
Most aftermarket heads today have the intake valve centerline moved away from the intake port about .100".......this was done to move the pushrod away from the post sidewall as most aftermarket head producers widened the port in that area to gain volume. The problem with this is now you have to split the difference between the intake and exhaust pushrod to center the rocker on the valve tip Left to Right.....this almost always doesn't happen with a standard width 1 piece Chevy guidplate.....so, in 2006, Dart came out with the split guideplate......now you can put each rocker dead to nutz on the valve tip I and E.......
Self aligning rockers are a solution too.....but I don't like them because it is better hold the pushrod steady because pushrods like to deflect (I hope you bought 1 pcs. .080 black oxide pushrods from Trend or Trick Flow, Comp, etc...).....
The split guide plates can be a bit tricky but just take your time......snug the rocker stud own lightly and use a brass rod to knock the guideplate one way or another depending on what you need.......when you are finished, one rocker will be straight (EXH.) and one will be cocked at an angle slightly.....this is normal.......
Now....I have to ask, did you properly measure for pushrod length?
Rocker stud length has nothing to do with pushrod length......pushrod length is determined be how tall the lifter plunger/cup (which is the product of the cam basecircle) is and how tall the valve is.....the rocker stud just holds the fulcrum.
Proper pushrod length and rocker setup is key to valvetrain longevity....where the rocker roller tip sits side to side and how it rolls front to back is critical and often overlooked by the novice....
Jebby, should you also tack weld the split guideplates after you get them aligned?
We did at the race shop years ago with a TIG....just to hold them and then numbered each guideplate....but on street engines I do not think it is necessary....just watch the plate when you final toque to make sure it doesn't move....but if you have concerns, by all means, run a little tack on them....
Summit says If Guide Plates Are Installed, the rocker stud boss will have to be machined down. Quote unquote, from their web site.
Looks like O.P already has his new heads installed. He is not going to pull the heads, get them machined, get new head-gaskets and install guide plates that are not needed.
Good grief.
Summit says If Guide Plates Are Installed, the rocker stud boss will have to be machined down. Quote unquote, from their web site.
Looks like O.P already has his new heads installed. He is not going to pull the heads, get them machined, get new head-gaskets and install guide plates that are not needed.
Good grief.
The heads are 165cc S/S Dart heads reboxed by Summit.....and they are machined flat to accommodate a screw in stud just like if you machined a press in stud head....and they will take a guide plate and Summit needs to revise their notification.....but you would know that if you actually machined a pair, or set them up....or actually put guideplates on them.....
Does it need guideplates.....I would say no, not really, unless you decide to spin it up regularly....since the pads are milled, I would put plates on them anyway.....just like if it were an LT-1 or L-82....especially with a big heavy roller rocker.....it keeps things stable....
Now the only thing I retract from the above statement about guidplates is that these do not have the shifted intake centerline....so a regular old small block guideplate will work fine....split not needed...
So...to the OP....do you need them, no....would I put them on, yes....
Summit is probably the largest purchaser of Dart heads there is......and they get the super deep deal......especially now that Dick Maskins has passed on......Dart gets $529 vs. $399 for the same head.......it is a good deal, but these need blending and cleanup to make any power........good news is that these heads respond like gangbusters to bowl blending......
So...to the OP....do you need them, no....would I put them on, yes....
It's not a good idea to mix the slotted alignment hole engineering intention provided in the cylinder head casting with at the same time the utilization of a steel guide-plate; this as if (and as inevitably they will) the two points of positioning don't agree as installed, then a bind-loading will be imparted which may lead to unacceptable wear characteristics or even failures of the componentry (particularly the pushrod) effected.
As far as the guide-plate being added under the stud, obviously its' only real effect is to raise the stud positioning height; first reducing the tread engagement and depth into the head casting, and which also leads to the requirement in considerations for: the shank to hex transition of the stud and the bottom profile of the rocker arm body, the rocker arm trunnion shaft to stud transition, available tread length(s) for the appropriate retaining fastener, and of course the total height of the stud and/or fastener for valve cover fitment, including baffles if present.
The rocker arm itself doesn't automatically change position.
Sorry for the late response. Just got back from the Carolinas. The heads are on the engine and not coming back off. I did talk to a couple of friends on the weekend. One suggested measuring the pushrod hole. He told me it should be no more than .340 side to side. I measured .320 on the old head and the new, so I'm going to go with the head guides since it's not going to be revd to the moon lol. Harden pushrods that's it. Jebby your right. There is a Dart Part # on the side of the heads. Don't know it off hand, but I think its 8-digit number. I looked it up once and it went back to Dart.
Kevin
Sorry for the late response. Just got back from the Carolinas. The heads are on the engine and not coming back off. I did talk to a couple of friends on the weekend. One suggested measuring the pushrod hole. He told me it should be no more than .340 side to side. I measured .320 on the old head and the new, so I'm going to go with the head guides since it's not going to be revd to the moon lol. Harden pushrods that's it. Jebby your right. There is a Dart Part # on the side of the heads. Don't know it off hand, but I think its 8-digit number. I looked it up once and it went back to Dart.
Kevin
That's good.....the pushrod is .3125 so you will have .003-.004 wiggle room left to right......more than acceptable......
Rocker alignment and heads.
