How To ID Solid Lifter Cam in The Car

[Paul C.]

I have a 71 LT-1 and was planning on adjusting the valves. The problem is I don't know what cam is in the car. Previous owner said he replaced the cam with a new one but same as original. How to I verify what I should set the valves at since I'm not sure what cam. Thanks

[William B.]

Re: How To ID Solid Lifter Cam in The Car

You can adjust the valves without knowing what cam is in the car. You just have to be sure if it's a solid or hydralic cam. Once you know that follow the procedures in the gm service manual.

[Joe L.]

Re: How To ID Solid Lifter Cam in The Car

I have a 71 LT-1 and was planning on adjusting the valves. The problem is I don't know what cam is in the car. Previous owner said he replaced the cam with a new one but same as original. How to I verify what I should set the valves at since I'm not sure what cam. Thanks

Paul-----


There is no practical way to ID which cam is in the engine with the engine assembled. You can tell if it's an hydraulic or mechanical lifter by determining if the lifter plungers can be depressed, but you cannot otherwise ID the cam. I would assume it's as the owner stated and set the valves accordingly. If it runs well thereafter, you'll pretty much know what cam is in the engine.

[Joe C.]

Re: How To ID Solid Lifter Cam in The Car

I have a 71 LT-1 and was planning on adjusting the valves. The problem is I don't know what cam is in the car. Previous owner said he replaced the cam with a new one but same as original. How to I verify what I should set the valves at since I'm not sure what cam. Thanks

First, determine whether it's a hydraulic or solid tappet cam. Run engine, to op temp and remove driver's side valve cover. With engine shut off, if all rocker arms are tight (within a few minutes of shutdown), then the cam is hydraulic. If some are loose, then it's a solid tappet cam.

As a second check for solids, stop engine at timing mark 0 degrees, rotor pointing to #1 electrode. #1 intake and exhaust rockers should be loose, and #3, #5, and #7 will have a mix of loose/tight rockers.

All solid tappet cams use different lash settings. If you set the lash too wide, you'll cause a mechanically noisy engine with smaller than advertised lift/duration, and an engine that produces better than expected low/midrange torque, but weak horsepower. If you set them too tight, you risk damaging the engine.

Vintage Chevrolet solid lifter cams used the following factory recommended settings:
Early Duntov: .012/.018
Late Duntov: .008/.018
"30-30": .030/.030
LT1: .020/.025

If you determine that your cam is solid lifter, then you'll need a dial indicator to measure intake/exhaust LOBE LIFT by measuring pushrod rise at the rocker arm. For the LT1, it is .3057"/.3234" I/E. Verification of lobe lift is no guarantee of actual cam installed without measuring durations as well, but it should eliminate most others.

It is possible, but very improbable, that the installed cam is a solid roller. You can verify that by removing the intake manifold, or with a dial indicator and degree wheel.

If you determine that you have an LT1 cam installed, there are many of us here who can give you the lash adjusting procedure developed by John H. and Duke W.

[Stuart F.]

Re: How To ID Solid Lifter Cam in The Car

Joe;

Where do your Factory recommended specs come from. Perhaps they have re-written the books since the old days, but I recall early Duntovs were speced at .012" and .018", then later came along .008" and .018". I always thought I was pushing it at .008" and .016" for racing. Boy! I must have missed a lot! I'm talking pre 64 here.

Stu Fox

[Brad M.]

Re: How To ID Solid Lifter Cam in The Car

Joe C:
It is my understanding that the cam for 70 lt-1 was different that 71 and 72 lt-1.

I believe the 70 lt-1 used the 30-30 cam:
lift .485/.485, duration.050 - 254/254, Adv duration 293/293 Lobe sep 114

and the 71-72 lt-1 cam has the following specs (with recommended lash setting of 20/25 as you indicated):
lift .459/.485, duration.050 - 242/252, Adv duration 295/308 Lobe sep 116

Is that correct/consistent with your belief?

[David D.]

Re: How To ID Solid Lifter Cam in The Car

Not trying to steal thread, but staying on the subject title How To ID Solid Lifter Cam, but mine is not in the car, but in a short block.

I have similar problem in that I don't know what cam is in the short block and I know it'd be real easy to pull timing cover etc....and pull cam. But, Do to circumstances beyond room here to explain, I can't.

So, Is there a way to ID the cam while still in the short block. No pan, no heads, no nothing 'ON' the block. Can I look internal through the bottom side with a mirror etc. and see some numbers? If yes, where about would I try to view? Front, middle, rear of block?

I'm 99.8635% sure that it's an origianal 30-30 Duntov, but really would like to make sure.

Thanks in Advance,
David

[Duke W.]

Re: How To ID Solid Lifter Cam in The Car

The LT-1 engine used the same 3972178 camshaft assembly (camshaft and indexing pin) for all the model years it was in production - 1970-72. The "ID number" for this cam is 2178, which is the last four digits of the finished camshaft part number. It may be possible to see this on the cam through an empty lifter bore with a good light or borescope. It is cast in between the lobes toward the rear of the camshaft. The 30-30 camshaft assembly is 3849346 and the finished camshaft is 3846347.

My suggestion is to measure and record the current lash. This can provide a clue. The lash must be measured astspecific crankshaft indexing points to be accurate (e-mail me for the instructions.)

Post your measurments and we'll go from there.

Duke

[David D.]

Re: How To ID Solid Lifter Cam in The Car

Duke,
I believe I have the The 30-30 camshaft 3849346.

My suggestion is to measure and record the current lash. This can provide a clue. The lash must be measured astspecific crankshaft indexing points to be accurate (e-mail me for the instructions.)

I'll send e-mail now.

Thanks,
David

[Duke W.]

Re: How To ID Solid Lifter Cam in The Car

My suggestion to check lash was for Paul. You said your engine is a "short block", so I don't think you can check lash if there are no heads/valvegear installed. You might be able to see the cam ID through the lifter bores.

Duke

[David D.]

Re: How To ID Solid Lifter Cam in The Car

I realize that....now. I read through the instructions you sent and at the same time realized the word 'lash' and its meaning.

Oh well, thank you for the great instructions anywho. Good author(s).

[Bill M.]

Re: How To ID Solid Lifter Cam in The Car

Joe;

but I recall early Duntovs were speced at .012" and .018", then later came along .008" and .018". I always thought I was pushing it at .008" and .016" for racing. Boy! I must have missed a lot! I'm talking pre 64 here.

Stu Fox

You are right, Stu: 283 Duntov is .012,.018, 327 Duntov is .008,.018

[Joe C.]

Re: How To ID Solid Lifter Cam in The Car

Joe C:
It is my understanding that the cam for 70 lt-1 was different that 71 and 72 lt-1.

I believe the 70 lt-1 used the 30-30 cam:
lift .485/.485, duration.050 - 254/254, Adv duration 293/293 Lobe sep 114

and the 71-72 lt-1 cam has the following specs (with recommended lash setting of 20/25 as you indicated):
lift .459/.485, duration.050 - 242/252, Adv duration 295/308 Lobe sep 116

Is that correct/consistent with your belief?

Brad,

The "30-30" cam was used in 1964-65 Corvette with L76/L84, and 1967-69 Camaro with Z28.
Same LT1 camshaft was used 1970-1972. Compression was lowered in 1971-72. Intake manifolding and carburetion had minor differences.

[Joe C.]

Re: How To ID Solid Lifter Cam in The Car

Joe;

Where do your Factory recommended specs come from. Perhaps they have re-written the books since the old days, but I recall early Duntovs were speced at .012" and .018", then later came along .008" and .018". I always thought I was pushing it at .008" and .016" for racing. Boy! I must have missed a lot! I'm talking pre 64 here.

Stu Fox

Stu,

Thank you.
You are correct, and I am incorrect.
I have asked John Waggoner to edit my post, as the edit function "times out" after about 12 hours, or so.

Joe

PS: It has been corrected.

[Duke W.]

Re: How To ID Solid Lifter Cam in The Car

The .008" inlet lash setting became the standard service specification for 1963. Prior to that it was an optional setting "for weekend sporting events".

Duke