[haley72]

Im currently in the process of building a 302 for my 72 Comet. The motor is running with the valve lash set at 20 on both intake and exhaust; All eight cylinders. It runs OK, but I know the lash is'nt set right. The cam specs I have are as follows; .491 int .512 ex 108* lobe separation and duration at .050". It is set at 2* advanced. It has 289 heads, the ones with the heart shaped combustion chamber, 1.6:1 ratio roller rockers with 289 push rods. Also, the timing is a little off. Every once and a while it will back fire through the carb. It is set at 10* advanced. Any help anyone could give me I would greatly appreciate.

[Guy Hiltz]

First you need the lash settings for your particular cam,assuming its a solid of course.Lash settings can vary from .030-.012.There is also the IOEC recommended way to set valve lash,although I dont have time at the moment to go into that,but tonight I can.If the lash is off on 1 or 2 valves it could account for the backfire you are experiencing.

[haley72]

The cam is a hydraulic cam with solid lifters. Don't ask me why the guy I bought the motor from went with that set up. Also, the valves are Chevy valves 202s and 194s. I dont know if that will make a difference.

[454C10]

You need to use the right lifters for the cam. Get a solid cam for solid lifters or buy a new set of hyd lifters for your current cam.

A carb backfire is a sign of retarded ignition timing and/or a lean fuel mixture.

[Rick WI]

A general rule of thumb with a combo like you have is .008 to .014 hot lash. The only way you can determine what it really needs to be is to have the cam analyzed with a cam doctor and software to determine the ramp profile. Cold lash would work out to around .002 to .008. Nobody recommends to run this combination unless you use a billet core, at least nobody that knows what they are doing.

If you are not running a billet core and lash will not stay in spec it's due to the camshaft flexing.

There is nothing wrong running this type of combination if it's excecuted correctly.

[cliff tate]

you will never get it right with hyd cam and solid lifters, the lobe profil is different. also ar you useing the early rockers or the rail type.the early 289 heads have slotted push rod holes(ala chev)and go withe non rail rockers. also ther is a difference with valve stem lenth. early non rail rockers use shorter valve stems. sounds like you should start over or you will have a disaster. cliff

[haley72]

The rockers are specificly for that head #1. #2 Is the heads are just the standard hole type for the push rods. There's no guild or anything like that. The rockers are stud mounted. The pistons have eyebrow notches for the valves and we had it running just fine with the lash set at 20 but it does back fire and spit through the carb. I dont know if its the valves or the dist being off. I know for a fact that the valve isnt set right for regular driveing yet. Thats what Im trying to fgure out. Once that is done if it still back fires then its the dist. If it didnt start at all I would think it was because of the solid lifters. If it runs right now WITH solid lifters; Why cant I use them? As far as starting over, I work seven days a week just to break even. So I kinda have to work with what I have. What do I need to do to set it up right or have I wasted my time?

[techinspector1]

Posted by 454C10:
"A carb backfire is a sign of retarded ignition timing and/or a lean fuel mixture."

Or an intake valve that isn't going all the way on the seat.

[Guy Hiltz]

Heres how to set solid lifter valve lash.It will be a lot easier if you remove the spark plugs and use a remote starter.Start at # 1 piston,rotate the engine until the rocker arm starts to open the exhaust valve,then check/adjust intake lash.To adjust exhaust lash,rotate the engine until the rocker arm has fully opened the intake valve and is 1/2 to 2/3's back down.Valve movement happens pretty quick,if you could turn the engine over by hand it would be even easier.Where you are using mixed cam/lifters you want to keep on the tight side of measurements offered up in earlier posts,at least as far as I know.You want to be able to slide your feeler gauge between the valve and rocker with a bit of drag,not too much,not too little.It takes a little bit of practice to do it right,the more you drive it the more often you may want to check lash.Although if everything is in tip top shape and quality parts are used,good pushrods,matching valvesprings,screw in rocker studs,etc..etc..,valve lash shouldnt change a whole lot.Improper valve lash will definetly have an effect on backfiring.

[haley72]

Everything on this motor is BRAND NEW. I have spent a lot of money making sure of that. The only thing reused is the timing cover. Even the stater is brand new and premium. I e-mailed Crower who is the maker of the cam and they said to adjust lash to .012" int and .014" ex. Does that sound about right? What is the difference between solid lifters and hydraulic? I have an idea but I have been getting some different answers from people. Also, every once and a while someone will through out the phrase "Solid Cam". If Im not mistaken; Aren't all cams technically "solid", I mean I know mine isn't hallow. (lol) What exactly does that mean?

[topfuel]

Haley, the advice you have gotten to change the lifters is correct. The main difference between a hydraulic and solid lifter cam is the take up portion of the ramp on the lobe. With a solid lifter cam, this ramp is designed to slowly take up the valve lash and then move the valve off the seat. With a hydraulic cam, there is no take up ramp since there is no clearance to take up. That is being handled by the lifter. You should never run solid lifters on a hydraulic cam or vice versa.
I realize this may not be what you want to hear, but it is the reality of the situation. You must change lifters at the very least. It would probably be best to replace both the cam and lifters.

Barry

[Guy Hiltz]

Cam cores are not hollow,all are "solid",this refers to how the particular cam core is ground,cam lobes are designed to work a certain way with a certain lifter.As a general rule of thumb,soild flat tappet cams require solid flat tappet lifters and hydraulic flat tappet cams require hydraulic flat tappets.It has a lot to do with the shape of the cam lobe.Some open real quick,others open a little slower.Theres a whole lot more to Cam Shaft science than what meets the eye.If you are mixing a hydraulic cam & solid lifters,you are somewhat in uncharted terrotories,it doesent matter how much $$$ you have spent.I am soon going to be on my third solid roller (matched) cam set up in my big block Chevy,I dont mix parts.Use the parts the cam is meant to use,or guess & go.Or start with a cam and matched parts.

[haley72]

Thats what I thought about the cam and lifter combo. I guess Ill order a set of high performance lifters. After I get the hydraulic lifters, what should the valve lash be? Like I said before, Crower said .012"int and .014"ex. Do those numbers still hold true?

[Rick WI]

Haley, you obviously don't have a clue what you are doing, not a rip just stating the obvious. As I mentioned in my post and Crower concurred with my range I suggested you lash that cam per the specs they gave you with the solid lifters. Although this concept may be greek to some on the board that combination is not uncommon and is actually something pretty effective in a street application.

Lash the valves per the specs Crower gave you.

[curtis73]

I agree with Rick. There are four types of lifters:

hydraulic flat
solid flat
hydraulic roller
solid roller

The cam MUST match the lifter type and vice versa... PERIOD. Solid lifters have lash, hydraulics don't. Roller and flat have vastly different lobe profiles and can't be mixed.