Hey everyone, I’m a little new to the Nailhead but not new to engines, dozens of builds etc. I have an .040 over 425 that was sonic checked, had 3 holes sleeved due to a massive failure when a valve dropped into #7 and took out 3 rods, skirts etc. I bought the car 64’ Riviera from a good friend who had all this done. It runs nice and was blueprinted, balanced assembled by Classic Jaguar here in Austin. It has the TA 112 cam now with the TA dual stage 1 springs. I am going to swap to a larger cam aka the Comp Thumper and am curious as to what the minimum reccomended piston to valve clearance is. The pistons came from Centerville aka Russ Martin and are .040 cast with 40cc domes and reliefs. The dome to chamber clearance is .065”. Sadly I don’t know much about the pistons and Centerville can’t tell me which ones they sold me and on their receipt it says “.040 pistons”.... no other info. Thanks again everyone.
Paging F85.... IMO, At least 0.060", 0.100" is safer. Some run as little as 0.030", many don't check it at all! Clearance is tightest about 10-15* btdc on the exhaust and 10-15* atdc on the intake. If one side is tight, you can advance/retard the cam to get it centered. Things get tight when you add duration and narrow the intake/exhaust lobe separation. Lift isn't really an issue. It's during overlap when things get tight. I had a hard time fitting a mild Poston NH400 cam with the thin head gaskets. Not many here have reported their v-p clearance numbers.
With stock Rods .045" is safe if you need to go that tight and you check the clearance of every valve due to minor rocker ratio differences and be dam sure your valve springs have the pressure needed for the rpm the motor will run. The most critical valve is the Intake as the rising piston and the opening Intake valve are closing in on one another during one peticular cycle . Needless to say a rev limiter can save you a ton of green!
Generally .080" on the intake and .100" on the exhaust are accepted as safe limits. Of course, this varies depending on the type of build and level of confidence. It is worth noting (for those that don't generally build engines) that this should be done with a head gasket on and the cam degreed in place using a checker spring, solid lifter and adjustable pushrod at 0 lash as you rotate it around the valve events. That way contact will not result in bent valves when checking clearance. Cheryl
OP: report back the findings after checking with clay/play doh. Good idea to double check radial clearance with the valves as well as depth, being that you have a non-OEM piston or cam. Also...since you didn't mind a phone call to Centerville, I bet Russ would be open to discussing his preferences to patronizing customers. All above advice is fantastic. Every engine might have oddities, esp. when a bore or head is potentially moved along with the non-original parts. I have seen some weird things before...
Thanks for the advise everyone. I was hoping I could avoid yanking the heads since this engine was just built. Had planned on checking clearance with a dial indicator and checker springs when I degree the new cam. 8ad-F85 I’m new to the Nailhead scene, my good friend who had this engine built just prior to my purchasing the car from him is the one who bought the parts via Russ @ Centerville. I have not spoken to Russ directly myself. My buddy did and they couldn’t recall which set they sold him. I’m more than happy to call them if you think it will help.
That makes so much more sense now (fog lifting from brain) I would call, being they probably use more of those pistons than anyone. My offering based on seeing odd machining and manufacturing issues won't be efficient to you in this case. The occasional aftermarket race block that might have the deck bolt pattern shifted from a true position, along with other performance part oddities are the type of things you discover completely by accident, from being really picky. I bet many things slip by unnoticed or as an accepted risk. The radial clearance issue is from valve reliefs or domes not quite in the right spot or when machining gets drastic and relocates parts that mate up at angles. I do not know if there's any likelihood with these on an nailhead, and that it isn't always felt when rotating an engine over assembled as you described. I have torn them back down for other reasons and noticed the slight impression into the piston completely fooling me the first time around. If Russ says there's zero risk, still be somewhat cautious because you might be the first to actually see it. They didn't machine your engine. I would not be afraid of tearing the engine down further... However... assuming it has run before without issue, you should be OK. If you feel persistent about some definite over kill for your seemingly straightforward swap, then a brief attempt to shine a light down the port or a $25 endoscope from Ebay might put suspicions to rest. Not that you'll see anything certain and I don't recall if you even can.... Now past that... Hopefully the increased overlap isn't an issue for this build because the fix is obviously more involved if you go ahead with it. I don't think you'll have any issues though. [Adding that I often jump right into builds done elsewhere from often finding other things to deal with, but you get a feel for where trouble might be. Many are just fine, there's usually a reason they end up being looked at of you catch my drift]
8ad-f85 Thank you very much for all the detailed feedback. This engine is in the car and driving great and presently has about 2000 miles and 3 oil changes on the rebuild. The only concern I have after reading some of Tom Telesco's posts is that this block is bored .040 (it was sonic checked first on holes) and 3 of the bores had to be sleeved to do the catastrophic failure it suffered. (swallowed #7 valve while getting on a freeway ramp) Tom mentions in several threads that anytime a 425 is bored .040 he fills the bottom of the block with epoxy to reinforce it, seems logical for sure, apparently not doing so will cause the rebuild not to last very long due to cylinder distortion. I confirmed with the builder that the block was NOT filled with epoxy after being bored and sleeved. Is it smart to pull it apart now and do it? With or without epoxy will this block be stable under any sort of boosted/turbo application? Assuming I swap in forged pistons etc..' Are the TA or Tom's rocker arms a good investment. Matt Martin told me on a thread that they are not strong and break not worth the $$. Again I do not have any opinion or empirical data to go by, as such I have to trust what knowledgeable folks her are willing to share with me. From an engineering point of view it seems they would be well worth the money if they are reliable and solve the geometry issue affording the us the "most" out of the cam. Again this is all assuming the heads can actually deliver at whatever lift it reaches... but just the added time spent mid-peak lift would seem beneficial on a flow choked head design?? Great idea on the endoscope, I have a nice HD unit that works great! Ill try that out and see what is visible. My plan has been to install the larger cam and run it as is for a while then maybe next winter pull the engine and go back through it. Other than the annoying lazy lifter that comes and goes it runs great. Smokes a tad (blue-oil smoke) on hot restarts after sitting for 10-15 minutes, there are no intake valve seals installed. I also believe some of it is caused by fuel boiling thanks to this ethanol crap which washes any oil residue in the intake runners down and burns it off on startup. There is no visible blow by and the engine does not consume oil to any measurable amount. If i pull it again: Have someone reputable port the heads (always money well spent IMHO) Port match and cleanup the intake to match the heads Install forged pistons to make it "power adder safe and obtain ideal compression" Turbo inter cooled just to be different and have an old school sleeper. Likely FI Tech EFI sooner or later, mainly to get rid of fuel boiling stink, being in Texas it gets fairly annoying to always have the car or garages filled with fuel vapors. Thanks again for all the feedback, really appreciated. -Rob
If you are thinking forged pistons then it could be short filled with whatever needed at any point. Machine grout, hard block, epoxy, etc.... It's too easy to not do. I fill most anything serious regardless. The area filled tightens up about a thou using grout type products. After it sets up you could determine if it still needs a hone, depending on ring travel, etc.. It is fresh yet. In my area, I can't get stuff like Embeco 885 without shipping a pallet, so various machine grout found at home stores is about $8/bag. Double check the data on expansion, etc., but it is literally made for the same purpose. That said...I re-read about the boost plan now. Better look close at what you're working with when apart. I'd be planning a tall fill being as good as anything and worry about oil temps when they prove too much. Also backtracking here...I tend to look at a few block candidates before accepting one as fit for duty. You may decide another plan for this block at that point. So you do have an endoscope and it's not being used for this already? I don't think I want to know....... Maybe you should send these really good pictures along for further study. There shouldn't be any oil residue in the intake to wash off. Might not be broken in/seated yet, but I don't like that. Could also be a chemical issue like STP or other additive preventing ring seal. Might be connected to the lifter problem. In no way am I disregarding the theories, I learn things everyday. I have nothing negative on the rocker arms. Here's the catch 22 on better rockers in general vs head porting. Whichever one done first when consecutively tested looks like the big hero because they both do the same thing as far as filling the cylinder is concerned. One gains big hp then the next adds a little more, then vise-versa if reversed. If it's a mild cammed, low output engine then either are tossing a bunch down the rabbit hole. I do and make both and am not in any competition so there's no agenda here. I still put head porting first, even on mild deals. Leaving too much of every possible low hanging fruit to ignore, even if I lose $$ on labor time. The customer always wins on that one. Any good rockers go a long ways towards geometry problems and valve guide or stem wear. If it's a reeaally big cam then both are encouraged. As far as rumors of breakage...would it be possible to work out your concerns with Tom? I can't imagine him leaving you high and dry after such an investment. If there were any issues in the past I'd suspect they'd already been solved or an opportunity exists to improve. Again, you never quite know what they are bolted to. Is it possible that people have added stands or components to a set up out there?
Rob, With MY FORGED pistons they are built for a .700" lift with ENOUGH RADIAL clearance for a 1.94" valve. No worry's about lift, duration, overlap, whether L or R or ROCKERS used. We ran .020" intake clearance on one of my friends "Nail" for yrs. with NO PROBLEMS. Since the piston is going DOWN & the intake is chasing it. Valve springs MUST be good. You MUST know what your doing as far as TUNE wise goes for ANY power adder with CAST pistons. They are NOT too forgiving. Just my opinion about the "Thumper" in the Riv. TOTALLY WRONG!!!! MANY conversations & thoughts on "Nail" cams. One that comes to mind "Do "Nails" need special cams". MUCH GOOD info there started by GSGTX. Tom T.
as far as rocker arms go, one car has Toms and one has TA never had a problem with either. the only ones that will break are the stock ones. specially with more spring pressure.
Awesome feedback everyone. I’m open to suggestions on the cam. I was looking at the TA 413 as well, but likely would need to wait until I swap over to a set of Toms forged pistons to eliminate clearance issues. The milder cam I was looking into is the TA-25. Glad to hear the news on the rocker arms. My initial plan was to use Toms rockers with the TA-25 cam for now. Enjoy it for the spring time then pull the engine next winter and send the heads out, either epoxy this block or source another for the turbo build when it’s time. I also had thought about ring seal. What’s odd is sometimes I have the oil smoke and other times not. Almost seems as if it’s valve guides and the lack of seals on the intakes. I know Buick added them in 66 but I confirmed mine does not have any valve seals. I am running Valvoline VR1 Racing High Zinc and an extra bottle of ZDDP additive from comp cams. I’ve also run one batch of PennGrade High Zinc
If so, you'll see that on the stems. Common problem with other makes too, the puff on startup. I've had it happen with fresh circle track type builds on the street with very low ring tension, no intake seals, loose clearances. No big deal if they spend much of their time not running under vacuum (not street ) I don't know that I would spend the $$ or time for a 1 level up minor cam increase mostly on the exhaust side. Do the intake mods for sure. The rockers will probably net you more increase and then you have them for the future. You'll be looking at the valve guides too. If you were thinking of swapping to the 25...you should be able to approximate cam specs within reason using the current one and comparing cam cards, with obvious defer to real world install.
Keep in mind that Toms Roller rockers have the higher ratio (up to 1.9 depending on pushrod length) while the TA rockers have the stock 1.6 ratio. I like the higher ratio to open/close the valves faster to get the flow going. The cam specs should consider the effect of the rockers..... you don't need a high lift lobe since the rockers will do that for you.
Just curious...I LOVE the sound of the smallest Thumper cam. What is the tradeoff of that longer 241 deg exhaust duration? I figured that would really wake it up in the mid range 3500+. I’m curious if you know what the sacrifice is down low? Or is it just a net loss across the board making the average power output across the usable range a negative?? Another forum member runs this cam in his 401 GS and loves it. I figured my 434 would mellow it out a little bit and still retain enougg grunt, but again I’m new to the Nailhead so the logic I’ve applied to all my other builds may not hold water here. I’m not out to win races, truthfully I just putt around and enjoy the car with the occasional rolling into the pedal for fun. I have a big block C3 Vette I’m finishing up next year that’s “quick” and a C6 z51 with a built and cammed LS2, and a 16’ Denali HD diesel truck that I’ve tuned to 530hp/1178tq with all emissions in tact, and an AMC 401 built up in a redone Grand Wagoneer, a 71 442 Small Block Clone (convertible) with ported w-31 heads, forged pistons .040, a much larger cam than the Thumper and 3.73 with 2800 stall. Pulls hard to 6400 and stomps 455 cars all day long unless they are really built up. So I’ve got plenty of other cars that are faster than my Rivi.
I'd be curious to see people's dyno sheets showing a higher overlap cam with short durations, advanced position, and some attention to the induction system on a large cube engine having long tube headers. The last thing you'd expect is loss of low end. I don't think a water brake dyno would even pick that up consistently because of the way they don't load up well at low rpm. I would believe that it could miss the mark approaching and passing peak hp though. The idea of overlap's benefit is to help the headers pull on the intake tract sooner in the cycle, so what looks like some pressure bleed-off on paper does the opposite in a spinning engine by increasing VE once getting past the rumpity idle. If not overcammed, they are supposed to wake up sharply. Not to be misunderstood, I'm not a huge fan of this cam line and how they universally apply it to all makes.
I thought I would do a follow up on this thread. I did end up going in with a cam very similar to the Comp Grind that I had ground. Specs are as follows Duration @.050 230/241 Intake .5424 Exhaust .528 109 LSA ICL I think is 104 I have to find my card and double check what I asked for. Its a tweaked version of the smaller thumper grind with .020 added to the lift on both sides and a little more intake duration. I widened the LSA 2 degrees to extend the power band a tad bit. It is tuned and runs like an ANIMAL now. It feels much like my built LS-2 in my C6 Z51 6spd Vette. I "Doc Modded" and ported/blended the intake runners Heads are stock other than good springs, new valves, and they are milled .030 total Pistons are cast from Centerville with a 40cc dome Dome to chamber is .060 Heads milled .030 Deck milled .020 Pistons are .025 in hole Head Chamber volume is 120 cc Static Compression is 10.744 (I have yet to get away with any more than 27 degrees total timing on 93 Octane @ 12.8:1 AFR TA Shorty headers, TA 2.5" Mandrel bent exhaust that I cut and re welded to locate the mufflers in the rear. Magnaflow High Flow Metallic Substrate Catalytic Converters (I just cant stand the damn stench of pump gas exhaust) and I could not feel any difference in performance before/after adding them. CB Performance Black Box Ignition Controller (Full 3D spark control via laptop mapping) 5 BAR MAP Sensor Stock distributor, vac advance deleted, mechanical locked out, points used to trigger the Black Box MSD 8mm Spiral Pro Wires custom fit 220 Amp Power Bastards Alt 4 row re-cored factory radiator and shroud w standard fan/clutch AC Car Vintage Air ST-400 (non SP) with Hughes 2000 Stall / rebuilt and valve body modified by me for quick, crisp shifts but not annoyingly harsh. Stock 3.07 (sadly open) rear --- need a posi badly as I can do rolling smoke shows in 1st from 30 a MPH roll. Dynomax Super Turbo Mufflers (no drone, and enjoy my audio system while driving) still sounds evil Edelbrock 1407 750 CFM carb (already had it laying around new in box or I would have used an AVS-2 series with the new annular boosters etc) I modified this carbs idle feed restrictors to provide a tad bit more idle transition fuel to cure the notorious big cam off idle flat spot/stumble that Eddys are famous for. Careful process slowly enlarging them with a jewelers drill bit and watching/logging AFR until it looked and felt good. Timing is ultra accurate using the Black Box, it allows me to set cranking timing at 15 deg, then advances to 21-23 once running at idle to achieve 15-16" Hg of vacuum even with the larger camshaft. I did a lot of tuning across the entire RPM range under all loads to dial it in perfectly. This box is awesome best $200 bucks I ever spent. The car is crisp and sharp as if it were fuel injected. Nothing I did with the curves in the stock distributor even came close to the results with the box. Best part is if the box fails for any reason I can flip a single switch I hid under the glove box area and it will revert to points/coil/condenser at 15 deg static timing to get me home. Overall I am ultra happy with the power curve it has. From Idle to 5600 it is just brutal torque. When the engine was built it had a TA-112 cam which was decent but was really wheezing by 4400 RPM. It felt like it had decent torque but to "make it rev" it felt like you were forcing it to do something unnatural. Complete transformation. Next I will port the heads. I have done a decent amount of porting etc but never on a nailhead, so either I do them myself and be conservative out of fear of trashing them/hitting water etc or find someone here who really knows them and have them done. I also love the nasty sounding / feeling idle
