Sorry for the long post, I’m hoping some of the engine gurus on the site might be able to help with a problem I’m having and want to give all the background. I am building a 69 coupe, which is not on the road yet as I’m still doing bodywork prior to paint, but the chassis and all running gear is completely finished. The engine that’s in the car is a roller cam 350 with Vortec heads. The engine was a used crate motor with minimal use. I stripped it down, did a dingle ball hone on the cylinders, changed pistons to flat top hypereutectic with Scat rods, new rod and main bearings etc. I put in a Comp hydraulic roller cam and reused the OEM roller lifters and pushrods. I cut down the valve guides for clearance and fitted new seals and also cut down the rocker stud bossed and tapped for screw in studs. Fitted new beehive valve springs and PRW roller tip rockers (1.5 ratio). The carb is an Edelbrock 750 which I already had and it has an MSD pro billet distributor which I picked up used.



The engine only had maybe 30mins of starting and running up and down my 250’ driveway as the car is not ready for the road, but I couldn’t get it to accelerate without backfiring and coughing and spluttering. While trying to troubleshoot this problem, I happened to take off the rocker covers and discovered that many of the pushrods were not pumping oil to the rockers, so I decided to put in new lifters as I figured they were not flowing oil like they should. I did have trouble priming the engine when I first assembled it, and it took something like 20mins of priming with a drill and old dizzy to get oil out of all the arms, and even then they didn’t seem to flow much. The engine has 50+ PSI of oil pressure at idle and I’m sure there are no oil delivery issues. When I removed the old lifters I found that at least two cam lobes had some pitting starting to develop on the leading edge of the lobes, so I decided to replace the cam. The cam Comp suggested was really too aggressive for the engine anyway, so I figured a milder cam would be a better choice. I ordered a GM ZZ4 cam which is machined from billet steel rather than the Comp’s cast core, and I got a set of GM USA made LS7 lifters which are the OEM replacement for the roller small blocks.



I’m still working to fix the backfire and stumble when trying to accelerate (that’s a whole other problem), but I’m intermittently getting a chirping/squeaking noise from the engine which I believe is coming from one or more roller lifters. It sounds a lot like a a pulley, but it’s there even with the belts removed and it seems to be coming from inside the engine. It’s happened a couple of times after a short accelerate and then the engine squeaks until it’s shut off. After restarting the sound is gone. I’m assuming one of the lifters is playing up but I don’t know why. I’m a little bit concerned that the valve springs may not be strong enough They have a seat pressure of 100lb and an open pressure of about 260lb with my cam. Do you think that could cause problems with the lifters even thought they engine is only being revved to maybe 3500rpm?

 

Where is the lifter in the bore height wise? Too high or too low can cause oil restriction......which in turn will not pump the lifters up......and cause the lifter body to hang up in the bore. The roller wheel itself is splash lubricated by the spinning crank and rods......
A cam that is used for a retro roller lifter setup may have a different basecircle than the factory style........
DO NOT run this engine anymore until you verify the situation......
Backfire and stumble may be the POS accel pump in the Edelbrock carb......replace with a viton piece.

Jebby

 

I've use LS-7 lifters in a later roller block. I've tried even 1/2 HP drills to prime a motor and you just don't get much to the top end. So I quit trying to do that 25 years ago. I just use the starter with the plugs out just before the initial run to prime everything for first fire up.

I follow what AFR says about H-roller spring weight. They from the factory install 140# seat springs for sub 235 degree cams limited to about 6000 rpm SBC Then up around 150# for heavier valve train like BBC or higher rpm SBC.

BeeHive springs run @ 20-25 pounds less and still have the ability to maintain valve control. So your 100# wasn't a good choice with heavy H-roller lifts. You could have very low rpm valve float.

When people ask me to come and look at a rough running new build. You have three areas. Electrical, mechanical, and fuel. Verify plug wires order, is the dizzy set with the rotor and damper about 15 degrees past the #1 cap pole and balancer on zero? Do you have the correct lash settings. Too tight and the valves never fully close and the motor will have back fire problems, Do you have vacuum leaks? Are you running over 5 psi to the carb causing flooding problems, EDl carbs are wonderful if you understand them, but you only want less than 5 psi.


When you first time fire your car you should already have the timing light on it to verify the timing.

 

Thanks for the replies. To clarify, this is a factory roller engine, so it has the dog-bones and spider plate to suit OE lifters. I'm confident that the lifters aren't sitting at the wrong level in the block and being starved of oil, the cam has a normal base circle diameter and the top of the lifters are just slightly above the dog bones when the valves are closed, just like the original ones were. Also there is good oil flow from the pushrods, so that seems to be fine. I'm thinking that the valve springs are probably too weak and a bit of valve float combined with the ramp rate of the cam might be causing a lifter to collapse a bit and the roller is skating on the cam rather than rolling smoothly. I'm going to remove the intake and inspect the lifters and cam. I guess I'll look at other valve springs with higher seat pressures.

As far as the backfiring, I have done quite a bit of work to try to solve it without much luck. Initial timing with no vacuum advance is set to 12deg BTDC and I have the springs and stop in the dizzy setup for mechanical advance of 24deg all in by about 3000 RPM. I've tried both ported and manifold vaccum for the advance canister but it doesn't make much difference. I've adjusted float levels, changed step-up springs and put a new accelerator pump in the carb but that didn't help either. The plugs are getting a lot of carbon build-up so it's running too rich even though I've carefully set the idle mixtures for the fastest idle then backed them off slightly leaner. I'm thinking of changing the carb to a Holley 600 or 650, as the 750 is probably too big and the Edelbrock carb is driving me crazy. But I suspect that the misfire/backfire could also be a problem with the distributor as I got it used and don't know for sure that it's good. The engine dies severely when accelerating, almost like hitting a rev limiter, however it only does it under load not revving when stationary. I've ordered a new tach drive dizzy so when that arrives I'll find out for sure I guess

 

I just realised is that the springs are rated at 100# at 1.8", but the installed height in these heads is 1.7" (which I just confirmed by measuring them), so the seat pressure works out to 130# and the open pressure will be 270-280#, which seems like it's probably OK? The valve lift of the cam is .474 on the intake and .510 on the exhaust.

I remembered that when I installed the new lifters, a couple of them didn't feel super smooth when I put them in the bores, almost like a bit of a burr catching as they went in. I probably should have looked closer at that at the time, but maybe that's got something to do with the issue?

 

First thing I would do is verify timing and firing order because that's easy to do. Next I would verify valve lash. Is the carburetor known good? The last and hardest thing to check is could your timing chain be a tooth off? Timing marks are not easy to see if you swapped cams in the car.

 

Kudos on jettisoning that cast roller! Me thinks your springs are a good choice for that ZZ4 cam and LS7 lifters. I may've chosen another steel cam; such as one from this selection of four affordable USA billet steel rollers ... perhaps 8802 or 8803 .https://www.summitracing.com/search/...rder=Ascending

 

Thanks for the reply. I've confirmed timing and firing order, they're definitely right. I know for sure the cam timing is correct also, I even have a photo of the marks lined up and I checked TDC with a dial gauge when the heads were off. What I don't know is whether the carb and distributor are definitely good. I think I'm going to swap both out to be sure. I need to put on a tach drive distributor anyway, so I've ordered one, and I'll find another carb to try.

 

Thanks for the reply. I think you're right that the springs are OK, as the cam doesn't have super high lift or duration. Those cams look good. I wasn't aware that the Summit ones were billet steel, but I see from the pics that they are. I'll keep them in mind for the future.

 

You didn't give the spring part number, but 1.7 installed height seems very short especially with .510 lift. What is the max lift of those springs and what is coil bind?

 

comp cams spring chart. COMP Cams Valve Spring Chart

You could use a beehive spring like 26995 and install it at either 1.750 or 1.700 and have lifter control. Above you were looking at things wrong. It's a combination of factors. High spring weights combined with high ratio rocker arms and too thin of oil, low oil pressure causes H lifter to compress the inner piston. Your typical H-roller cam doesn't ever have lobe ramps so steep than it can compress the internal piston especially with sub 140 pound pound springs.

you adjust the oil pressure with oil weight. like if you have 20 psi at idle with 5W30 oil going to 10w30 might make it 25 hot or even going to 10w40 or 15w40 You need oil pressure to keep from bleeding down h-rollers. Keep the wheels oiled

 

Thanks for the info. I have really good oil pressure, about 45-50 psi at idle with 10w40 oil, and 70+ at higher RPM. The valve springs are rated for coil bind at 1.1" and max lift of .560" at 1.7 installed height. 1.7" is standard for stock valves in Vortec heads.

Yesterday I pulled the intake and removed the lifters and everything looks perfect. The wheels on the lifters look brand new and the cam lobes have normal looking shiny lines developing where the rollers track on them. Based on that, I don't think the squeaking I heard was the lifters at all, but I don't know what it was. Glad I checked the cam and lifters for my own piece of mind though.

Something I did notice was that it looks like the backfiring is coming from cylinder 3, as there is a lot of dry carbon in the intake port on that one cylinder. The others are much cleaner, but do have some oil residue, which I think is because the PCV I was running seems to be flowing too much air and sucking a lot of oil. I'll just use a breather for now while I get the engine running right. I have done a compression test and all cylinders are around 190psi. I have a feeling that I have an ignition problem with cylinder 3.

 

and stock / OE L31 vortec roller springs are ~ 80 lbs on seat ... virtually same pressures as in OE HFT motors

 

Thats good for ZERO performance motors like L31 vortec. But the poster has some duration and over .500 lift with heavy valves. GM performance has very specialized super light weight valves Like in their LS7 and other performance h-roller motors. Us mere mortals don't have roughly half the weight titanium intake valves and hollow sodium filled exhaust valves.

Jan 18, 2018 · Valve Spring Style: Beehive (LS7 specific) Valve Spring Color: Natural: Valve Spring Seat Pressure: 100 lbs. @ 1.960 in. installed height: Valve Spring Open Pressure: 310 lbs. @ 1.370 in. open height: Valve Angle: 12 Degrees: Intake Valve Material: Titanium, hollow stem (chrome nitride PVD coated) Intake Valve Dia. 2.205 in. Intake Valve Weight: 77 grams: Exhaust Valve Material stainless steel sodium filled 74 grams.

I just looked up my Manley proflow light weight valves and thy are 134 grams I and 126 grams exhaust. So Big people like AFR through lots of testing use exactly what I posted above for spring pressures. I also stated that BeeHive springs use 20-25# less spring pressure and can still control the valves. You are not going to get away with 100 and less pounds unless you have a very low performance motor.