need valve lash advise if I don't know the cam

[Joe C.]

Re: need valve lash advise if I don't know the cam

Clem, I know it's a micrometer but what specific tool is that.

It's a dial indicaterometer, aka, lifter plungerometer!

[Ian G.]

Re: need valve lash advise if I don't know the cam

I'm thinking its a gizmometer

[Clem Z.]

Re: need valve lash advise if I don't know the cam

Clem, I know it's a micrometer but what specific tool is that.

it is a dial indicator that plugs directly into the lifter bore to measure the cam lobe lift.the part on the left move up and down on the cam lobe and move the dial indicator to read the lift in thousands of a inch

[Duke W.]

Re: need valve lash advise if I don't know the cam

Ian,

Measure it at the tappet, NOT at the rocker arm.
Loosely install each head, temporarily, and loosely install pushrods.............this should be done ONLY AS AN AID, SO THAT YOU CAN SEE THE AXIS THAT EACH PUSHROD IS ON. I can not stress too highly, how important perfect alignment with the pushrod axis is. If the thrust axis of the dial indicator is off, by as much as 2-3 degrees, it will give you lower readings.....simple geometry

Possible GM solid lifter cams installed:

Part Number.....................AKA.................... .Valve Lift*..................Lobe Lift##

3736097...................... "Duntov"....................395/.401
3849346......................"30-30"......................485/.485.................3235/.3235
3972178......................."LT1" .......................459/.485.................3057/.3235


## Lobe/valve lifts MAY be coincident with certain aftermarket cams.

* Divide valve lift by 1.5 to calculate lobe lift.

The "error factor" is equal to the cosine of the angle between the indicator plunger and the lifter axis. The cosine of 3 degrees is 0.99862, so the measured lift will be off by 1.5 percent, which is about the factory tolerance range. You don't need to measure the indicator plunger angle error with a Theodolite! Just eyeball it coincident/parallel to the lifter axis as accurately as you can.

The nominal gross lobe lifts in inches are as follows. Maximum mfg. tolerance is about +/- .002", and there could be a few thou of wear.

Duntov: .26250/.26650
30-30: .32336/.32336
LT-1: .30572/.32336

Measuring lobe lift is not hard, but if you've never done it before it may take a few rounds to get comfortable with the technique. Measure several inlet and several exhaust lobes. If the data is consistent it's probably okay.

If the inlet manifold is off measure at the lifter. If not measure at the pushrod socket on the rocker arm.

Compare you data to the above lifts. Can you reasonably conclude, taking into account mfg. tolerance, wear, and measurement accuracy that the data jibes with one of these three cams?

If not and you are confident that the measurements are reasonably accurate, it's probably some other cam. If it's an OE cam it can probably be IDed. If an aftermarket cam, it would be tough as there are hundreds of different designs.

Duke

CORRECTION: The lobe lift measuring error if the indicator axis is off by 3 degrees is 0.15 percent, not 1.5 percent. A 1.5% error is a cosine of 0.985, which is just under 10 degrees angle error!

[Duke W.]

Re: need valve lash advise if I don't know the cam

The "error factor" is equal to the cosine of the angle between the indicator plunger and the lifter axis. The cosine of 3 degrees is 0.99862, so the measured lift will be off by 1.5 percent, which is about the factory tolerance range. You don't need to measure the indicator plunger angle error with a Theodolite! Just eyeball it coincident/parallel to the lifter axis as accurately as you can.

The nominal gross lobe lifts in inches are as follows. Maximum mfg. tolerance is about +/- .002", and there could be a few thou of wear.

Duntov: .26250/.26650
30-30: .32336/.32336
LT-1: .30572/.32336

Measuring lobe lift is not hard, but if you've never done it before it may take a few rounds to get comfortable with the technique. Measure several inlet and several exhaust lobes. If the data is consistent it's probably okay.

If the inlet manifold is off measure at the lifter. If not measure at the pushrod socket on the rocker arm.

Compare you data to the above lifts. Can you reasonably conclude, taking into account mfg. tolerance, wear, and measurement accuracy that the data jibes with one of these three cams?

If not and you are confident that the measurements are reasonably accurate, it's probably some other cam. If it's an OE cam it can probably be IDed. If an aftermarket cam, it would be tough as there are hundreds of different designs.

Duke

CORRECTION: The lobe lift measuring error if the indicator axis is off by 3 degrees is 0.15 percent, not 1.5 percent. A 1.5% error is a cosine of 0.985, which is just under 10 degrees angle error!

Another member pointed out the order of magnitude error I made in my previous post. I added a correction note.

With care setting up the indicator one should be able to achieve a much smaller angle error than 10 degrees by just eyeballing.

Duke

[Clem Z.]

Re: need valve lash advise if I don't know the cam

Many name-brand aftermarket cams are I.D.'d on the rear of the cam. Usually contains the maker, grind #, and LSA on more recent cams. If the engine is out of the car, and flywheel off, remove the cam plug and have a look. You'll need a new cam plug, though.

Regards,
Dave

some times it is also on the end of the cam under the timing gear

[Clem Z.]

Re: need valve lash advise if I don't know the cam

Really? I've observed goodness only knows how many cams since I started building engines in 1969. Still do about 6 a year. (Did 10 this year). I have never seen a cam I.D. under the gear.

While it could be placed there, I doubt it ever would be. 3 bolt holes, 1 dowel pin hole, center-pilot hole, reduced diameter for timing gear pilot, which reduce the 'area' available, and the inscriptions cause a surface irregularity that would interfere with gear seating, are all reasons why that end of the cam would never be selected over the other.

Yes, it could be under the gear. But probably isn't.

Regards,
Dave

i have seen several comp cams and isky cams both roller cams with the specs under the cam gear. the specs are burned in with a electric pen.

[Clem Z.]

Re: need valve lash advise if I don't know the cam

i considerate a day lost when i do not learn something new.

[Ian G.]

Re: need valve lash advise if I don't know the cam

I bought a dial indicator off of amazon and they sent me a different one than I ordered. It has a snake with a cable instead of adjustable rods, and the dumb thing broke. Anyway, I took a few measurements before the thing broke, and they ranged between .2800 and .2950. I couldn't get it adusted at the right angle, so if I had the thing at a slight angle would the measurement be less or more than the true rating most likely? I'd think it would be less than indicated if it was not perpendicular in both dimensions? I'm going to return the dial indicator and see if I can find one that fits directly in the lifter bore.

[Duke W.]

Re: need valve lash advise if I don't know the cam

Reread the thread. You can probably get an acceptable dial indicator at Harbor Freight.

Duke

[Clem Z.]

Re: need valve lash advise if I don't know the cam

order one of these from your local speed shop or summit. http://www.streetsideauto.com/produc...NON&Reset=True

[Ian G.]

Re: need valve lash advise if I don't know the cam

The bore dial indicator I got sticks a little (I'm having really bad luck with these dial indicators), so I'm not 100% sure of the accuracy, but the measurements I got were around .31/.32 so it looks like I have an LT-1 CAM in there. Will this cam vacuum be OK for a fuel injector, or should I consider changing out the cam with a duntov cam? I heard it isn't too difficult to change out the cam.

[Duke W.]

Re: need valve lash advise if I don't know the cam

The LT-1 cam has about the same effective overlap and idle vacuum as the Duntov cam, so it should idle okay. I would worry if it's a 30-30 cam.

Duke

[Ian G.]

Re: need valve lash advise if I don't know the cam

Hey Duke,

I know you really like the LT1. Never having owned an old corvette, I really like the idea of having it the way it was in 1959...or as close as possible. Will the fuelie sound and drive the same with the LT1 cam in it?
I have the engine almost completely disassembled to put on the correct heads and water pump, so putting a repop Duntov cam in it wouldn't be much trouble... I read the '097 has a very unique sound to it.

thanks for your advice as always,
ian

[Duke W.]

Re: need valve lash advise if I don't know the cam

Hey Duke,

I know you really like the LT1. Never having owned an old corvette, I really like the idea of having it the way it was in 1959...or as close as possible. Will the fuelie sound and drive the same with the LT1 cam in it?
I have the engine almost completely disassembled to put on the correct heads and water pump, so putting a repop Duntov cam in it wouldn't be much trouble... I read the '097 has a very unique sound to it.

thanks for your advice as always,
ian

Just do it...