pushrods

I took my car out for its first runs down the track Saturday. I've put together a 525ci Pontiac, 8-71, TH400, alcohol Enderle Bird and system flowed by Gene Adams in my 74 Firebird door car. Due to funding I left the flat tappet cam valvetrain in place that I'd run in my blown/gas combination for years. On the first pass it left by my account fairly smooth but broke up on the second half of the track. I pulled all the plugs, none looked hot, none looked lean - nothing burnt off at all. I noted #5 looked new - hadn't fired, so I assumed possibly a bad plug or wire. The wire ohmed good, and I didn't have a replacement, so I put in a new set of plugs and tried again. The second pass it did the same thing - broke up when the rpm's came up, so I thought possibly it was fat. I turned up the blower a bit. Third pass it broke up hard so I lifted about 300ft out. I noted after lifting oil pressure was down around 15psi so I shut off. Back in the garage I pull the valve covers and note 8 of 16 pushrods are bent and/or broke. Inspection of the pistons and valves shows no sign of mechanical interference. The crank and rod bearings all look like new - good news pressure loss only due to loss of valvetrain. Any ideas what might cause the pushrods to break? They're standard 5/16" .080 wall Smith Bros. pushrods that I ran in my blown/gas combo for years. Is there something different about an alcohol motor that requires a bigger pushrod? I'm going to a roller before it hits the track again, but I'm lost on what caused this parts failure and would like to figure it out before I run it again and hurt more parts.

Sorry for the long post. Any help appreciated. Any info necessary let me know.

 

I had a problem similar years ago on a hemi. Checked everything and it would bend the pushrods warming the engine up. Changed the cam and problem was solved. Does seem like your pushrods for a blown alcohol motor are on the small side. What is your valve seat press on the seat and open. Be sure the springs are not coil binding.

 

which push rods are broken
intake , exhaust or mixed
Claude

 

Both intake and exhaust on 4 cylinders, both sides of the engine. Breaking on warm up sounds likely as I'm fairly certain #5 has never seen combustion. They're Isky springs with 120# on the seat, plenty of room for no coil bind. I'm not sure what they are over the nose - can't remember, but it's nothing exotic just plane jane flat tappet cam numbers. I ran this valvetrain for a few years successfully blown/gas so the basic geometry and clearances are good. Cam is an Isky blower grind 274/284 @ .50 on a 112lsa which I wouldn't think would be 'unrunnable'.

What might cause them to bend on startup? I think this may have been what happened, but I'm just trying to reason why. Hydraulic action? Wouldn't that show something on the bearings?

Maybe I just need better parts?

It did go 3 tenths better than the gas motor ever did, apparently running on 7 cylinders, half the blower drive I used to run, and missing badly on the back half of the track - so I'm intrigued to get it hitting on all 8 to say the least

 

What about timing , how much are you running ? .

 

25deg total locked out. Damage occurred at 10% overdriven - about 11psi boost. 13.25:1 static cr.

 

Had the same issue of pushrods bending/gaulding while warming it up and found that by properly priming the oil system and letting it warm up before you whomp it kept it from hurting the valve train. On our rocker arm assembly, you can take off one of the bolts, take a blue oil squirt can, and fill the rocker arm itself up until you can see it oozing out of the rockers, then prime the oil system with the starter before pulling the wire...

 

I have a 3qt accumulator on the car that I prime the oil with each time I start it - motor never spins over without 15-20psi pressure. I'm not running that heavy of an oil: Rotella, Delo, or Delvac 15/40 diesel oil - whatever is on the shelf. That's another question.... is that a suitable oil, or is there a preferred type with an alcohol engine?

I'm thinking/hoping maybe it's as simple as too much compression and cylinder pressure for the smaller pushrods. I'll put an upgraded valvetrain in and recheck every clearance before startup next spring.

 

They're Isky springs with 120# on the seat

I could be wrong, but 120lb of seat pressure on any kind of blower application seems low.

 

I hear you there and understand the whole boost per sq. inch of valve area deal, but I ran various solids in the blown gas combo since 1998 with this style spring and up to 15psi boost. My initial tune up on the alky motor was on 10-11lbs boost. Unless there is something different about alky I don't see that as a factor. I'm wondering if the added static cr is simply too much for the smaller pushrods. Thanks to all for the input - at least I know I'm not alone with this issue, and that it wasn't a 101 simple question that I should have known already.

 

That seems like a ton of compression for a blown motor. Many guys in blown alcohol are running less than 12-1 these days and I have heard rumors of guys at less than 11-1. The screw blower guys are running over 300 #s on the seat some even higher. Dave Germain

 

So are you saying that the high cr is the problem, or just advising against running higher cr in general?

 

......120# of seat pressure woooo I would be very scared If I get under 325# of seat pressure we pull them and save them for the exhaust..If my daily driver had only 120# it would scare me!!!!!!DaveLowe

 

You guys understand I'm running a flat tappet cam - not roller stuff. If you put 325# seat pressure to a flat tappet cam the lobes won't last long.

On the static cr deal I opted for the higher cr because I don't intend to get into a the high end 14-71 high helix or 40-60% overdrive stuff. I'm just tinkering with the hobby running my little 8-71 on a 525ci in the 10-20% overdrive range - maybe 16 or 17psi boost. I could put a thicker gasket in and drop it down under 12.5, but I would guess it'd be slower overall - and likely no easier on bending pushrods which is my problem at this time.

I'll be putting roller stuff in next spring with all kinds of spring pressure and fairly long on the duration to crutch my small ports - which should knock the effective cylinder pressure down further. Someone speak up now if the consensus opinion is you can't run 13:1 static with blown alcohol and limited overdrive. I'd been lead to believe it was appropriate by the tech where I bought and setup the blower. In fact his advice was to by no means go lower than 12.5:1 with what I was intending.

 

You have a point about the flat tappet cam and higher pressure valve springs. Is there a possibility that you are experiencing some valve float with the soft springs and that is bending the pushrods? Are there any marks on the pistons from valve contact? One of the hallmarks of race cars is the search for the weak spot. Most guys would put a heavier pushrod in the motor until they don't bend anymore then there will be a different weak spot to fix. I have seen that as I fix one problem another crops up. Eventually I will have reengineered the entire world then I can take a weekend off. Dave Germain

 

You Pprobably Need To Put A Roller In It With Heavy Pushrods. We Ran 7/16 .080 With Our Chevy Stuff. With That High Static And Just That Little Amount Of Boost I Bet Its Knocking The Exhaust Out First Which Then Contacts The Intake Pushrod. I Bet If You Did Get A Pushrod To Stay In It Would Flatten The Cam Due To The High Cylinder Pressure

 

Shawn is right on the money about needing stronger pushrods to open the exhaust valve against the increased cylinder pressure on the combustion cycle holding it closed. The pressure is not relieved until the exhaust valve opens and lets it out.
This problem crops up often on street cars when adding Nitrous Oxide systems.
I think the valve spring pressure is to low also. And consider that 120 is the number you started out with not what you have now after how long.
With the cam and lifters all mated to each other ( broken in ) You can up the spring pressure to 135 - 140 lbs. with out problems with good oil. Multi grade non synthetic oils and flat tappet cams are not considered a good mix.
Long ago I did 12 1/2 to 1 compression in a 468 cid wedge motor on alcohol with 26 lbs of boost, ran easy low 7's in a 1955 lb car, it just used up lots of number 2 & 4 main bearings. Plus retorquing the aluminum heads every pass. It was 12 1/2 only because those were the parts I already owned when it was built on a small budget.
If I ever wanted to build it again I would go 11 to 1.
Dropping the compression with thicker head gaskets is not a bad idea. SCE is a good source for extra thick head gaskets. And will give you a chance to clean the carbon from the gasoline off of the pistons and the combustion chambers.
You can always add more boost to up the running cylinder pressure.

 

Going to a thicker head gasket is a way,but watch for getting your quench too far out of wack.When the quench gets out of the optimum .040 on a wedge,it will cause it to detonate easier. 135 to 140 seat pressure is optimum on a flat and 400 open.Old fuel cars had flat tappets,but they didnt have much lift or duration and used heavy pushrods.If it starts breaking lifters, its detonating.Check to see how much seal and or guide to retainer clearance you have also.Check out what your running comp is with 11 lbs.It looks like 23.16. Final Compression Ratio (FCR) = [(Boost/ 14.7) +1] x CR. Also depends on what alt you run at on final
Corrected Compression Ratio = FCR-[(altitude/1000)x 0.2]

 

Understand on all points everyone mentioned. You guys are confirming what my hypothetical's were telling me - I just don't trust my hypothetical's yet as I'm new to alcohol and want to insure I'm not missing something. The exhaust going first trying to pop against the pressure makes sense - the intake would go next with nothing leaving the cylinder.

I mentioned earlier there is zero signs of any mechanical interference. The 120#'s on the seat is where they 'settled out' at - started at 130#'s. Also #5 never fired, so it kicked the pushrods on initial startup. The rods and mains all look like new still.

Interesting on the multigrade oils non-synthetic not being good for flat tappetts. I've run the commercial grade oils for at least the last 10yrs without any failures while others around me have flattened cams with the 'racing' oils they pay premium prices for. I'm always looking to learn something new though if you can elaborate?

Cometic makes good gaskets for us Pontiac guys. I'm running the .040" now but they've got alot of thicker selections as well.

Why would BDS who's been in the blown/alky deal with the like of Oddy advise me literally to not even waste my time below 12:1? The comment I remember when I mentioned I planned to run 11:1 is why don't you just run it on gas then? They advised dynamic cr's approaching 30:1 were obtainable and with me running in the mid/low 20's I'd be safe? I won't mention names of who I spoke with but the gentlemen has been around the stuff for many years.

Is there simply many schools of thought out there on how to approach this stuff? Or have I built myself a tempermental grenade?

Thanks again for all the input.

 

Not sure whose engines the guys at BDS are building these days if anybody's . I doubt if you would ever see a blown engine come out of Jims shop with the amount of compression you are running . I think you would be suprised at how much compression the blown alky guys are NOT running these days .