Hydraulic Roller Lifter Questions: I'm assuming piston-to-valve clearance cannot be accurately checked with a hydraulic roller lifter and a valve check spring using the clay method on the piston. Is this assumption correct? Can the clearance be checked with a hydraulic roller lifter, a valve check spring, and a dial indicator by measuring at 1* increments from 15* BTDC to 15* ATDC at valve overlap? If neither of the above methods work, how do you check piston-to-valve clearance with a hydraulic roller cam? Head Install Questions: I was planning to install the head without the head gasket and then add the compressed thickness of the head gasket I'm planning to buy to my measurement. I figure this way I can increase the thickness of the head gasket, if I need to, to achieve the proper clearance without having to buy two sets of head gaskets. Are there any concerns with this approach? Do I have to fully torque the head to get an accurate clearance measurement, or can I just snug the bolts? Thanks, Jim
Since your block is assembled the first step is to check and noted the deck height of all the pistion's, has this been done? I prefer the clay method if your running enough valve lift to access the valve notches . The clay will allow you to check the radial clearance also . .020"is enough, but Intake valve piston notch porting can pick up power if you have compression to spare and deep valve notches.
If youre not using a head gasket you can just snug the bolts. And assuming the check spring has less pressure than the lifter cup spring, then the method you describe should work.
Running a lot of duration on zero deck here... Warning...with the head bolted down and zero lash, if you get carried away and rotate the crank to the point of valve contact, you may bend a valve if you find interference. What I do is place the clay, and place the head on the dowel pins with no fasteners and no gaskets on a front cylinder. Then rotate VERY SLOWLY. If you find interference, the valve will simply lift the head off the deck, then you have to determine if added clearance from the head gasket will be enough to eliminate interference and give you the clearance you want, so repeat w/used gasket and again, no fasteners. Work your way up checking clay all the way to final torque w/used gasket. That clay measurement is what the engine will see once assembled. If I remember right, the usual point of trouble is the piston chasing the closing exhaust valve up the bore during the exhaust stroke. Added ex valve duration = piston and valve getting closer during that cycle. Devon
Steve - Yes, I've already checked all my deck clearances and have identified the problem child (so to speak). You mentioned 0.020" clearance being enough. I thought the rule of thumb for clearance is 0.080" for intake and 0.100" for exhaust. Did I misunderstand the clearance you are referring to, or perhaps are the numbers I cited incorrect? Also, as Dano mentioned, can you clarify the "piston notch porting" statement? Thanks. Rhett - I was contemplating the same thing. Since clearance issues occur at low lift, the force in the check spring should be very low ... however, I have no sense of how strong the lifter cup spring is. Technically, even a low force will compress lifter cup spring. How much depends on the strength of the lifter cup spring. It could be 0.0001" or 0.020", I have no educated guess for that. Devon - Thanks for the advice. I didn't even think about the possibility of damaging a valve during the check.
I have a solid lifter I use for this with an adjustable pushrod, but its been my experience that he checkers are generally weaker than the lifters. simple way to confirm is to watch the lifter cup in relation to the retainer at full lift. if it's sunk, then understand what that'll mean. if it's sunk .030 or so, and youve still got .200 clearance then not much..
I'll jump in on this. Picture the combustion chamber as the piston nears TDC and the intake valve is opening. There is HUGE negative pressure in the combustion chamber due to the exhaust scavenging effect. As the intake opens, the flow is around the intake valve and seat, and it's seeing impediments to flow such as the nearby chamber wall ( intake valve shrouding) and flow may also be impeded by the nearby piston.....this is where the shape/depth of the piston valve notches can effect the flow. Here's David Vizard's chart showing the negative cylinder pressure (red) and the burst in seat velocity (green) as the intake valve opens at around the 330* mark. It's been said that the initial intake valve opening flow is significant to performance! It's not just the heads that affect flow.... the piston can affect flow at this critical point since it's in the flow path.
Thanks - Makes sense I'd just never seen it referred to or even realized optimizing that was a thing or how you'd go about doing so.
Excellent info. Sorry if a bit off topic. To add, even some of the OEMs went so far as to relieve the top edge of the cylinder bore to give more valve relief, sort of a continuation of the relief in the combustion chambers. I know BBC did it, probably others too. I did it to my 436 to compliment the extra valve relief done on my 430 heads during the stage 1 valve upgrade. Just gotta make sure your mods don't interfere with the swept area of the top piston ring, and of course, the head gasket. Images courtesy of https://www.offshoreonly.com/forums/general-q/357215-bore-notching-454s.html Devon
Just note that the effect shown in Vizards graph ( in post #8 ) of producing VE numbers above 100% will not take place when breathing thru Exh manifolds . Most street strip motors breathing thru Exh manifolds are lucky to top 85% VE.
Bigpig455 - Watching the lifter cup makes sense. Thanks! The bore notching is very interesting. It’s something I never heard of before.
