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

[Ian G.]

hi guys,

I have a 59 fuelie 290 hp and am about to install the correct heads with the help of a friend. I have checked the lifters and believe that they are solid lifters. I also contacted the owner of the car from before the previous owner, who actually rebuilt the engine. He could not remember for sure if the cam was the early Duntov cam or not. So I see on some other threads that depending on what cam you got, there are four different possible valve lash settings as suggested by Duke Williams:





Now I read that if I make the valve lash too loose, then the valves will rebound to fast and end up beating up the valve seats and if I make it too tight, they won't close all the way and end up burning them out. So what is the best course of action? Seems like looser is better than tighter...

If I set it too tight vs too loose what might I hear or detect from the engine to know I'm on the wrong track, before really screwing something up?

Is there any way to tell if I have an 097 cam or otherwise by pulling the oil pan?

thanks!

[Joe C.]

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

Ian,

Without removing the cam, and lacking any possible identifyer thereon, you can measure lobe lift. This will tell you most of the story, but is not absolute, since you will not be measuring duration.
In order to do this, you'll need a dial indicator. It is imperative that the axis of the dial indicator be EXACTLY coincident with that of the pushrod. It is better to measure it directly at the tappet. If you measure it at the rocker, there is no way to keep the instrument's axis in the same plane because the rocker ratio changes during its travel.
If you have a degree wheel, you can also measure duration. This is much more difficult. I have never done so, and suspect that any meaningful results can only be obtained with precise and specialized equipment.
If you remove the cam, and there are no identifyer numbers, paint dabs, etc on it, then you can use a 2" micrometer, or outside caliper to measure lobe lift.

If you know the base circle dimension (unlikely) then you subtract it from the measurement across the nose-and-heel. If you can determine the manufacturer if the cam, they should be able to give you their base circle dimension.

[Duke W.]

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

If the heads are off the manifold is off. Remove the fourth lifter from the rear and rotate the engine until you can see the finished camshaft number, which is between the fourth lifter from the rear and the #4 journal. Get at least the last three digits. A borescope will help. If there is no casting number it's not a GM original cam and will have to be IDed in another way.

Another way is to set up a dial indicator on the lifters. Eyeball the indicator plunger to be as close to coincident with the lifter axis as possible.

Find the base circle, zero the indicator, then rotate the engine until you find peak lobe lift and record the data. Do at least two inlets and two exhausts or more until the data is consistent.

The '57-up Duntov finished camshaft number is 3736098. The camshaft and dowel pin assembly - what was sold through service parts - is 3736097.

Let us know he results.

Duke

[Ian G.]

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

OK, guess I needed to drain the oil anyway so I can restore the oil filter can... Thank you for the tips. I will get on it and let you know... I'm hoping I can see the casting number without the borescope. $200 on ebay. yikes.

[Ian G.]

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

Well, I drained all the oil, pulled the fourth lifter from the rear (starting from the rear counting 1,2,3,4 and pulling the fourth) and rotated the pulley and all I can really see is the lobe spinning. I imagine its going to be on either side of the lobe. Would it be in front or behind the lobe? I can't imagine being able to see the number with my bare eyes though. I can only see a tiny bit of the crank on either side of the lobe

So I guess the next step is to mount the heads and try the dial indicator? Or is there something else someone can think of for me to see to the side of the lobe without buying that borescope (very expensive)?

Thanks for all your help!

[Stuart F.]

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

Ian;

Any chance you can rent or borrow a scope? Some of the tool rental places may have them.

Stu Fox

[Ian G.]

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

I guess I could. I doubt Home Depot has one though. I'll look around...

[Ian G.]

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

Hey Stu,

Well, I checked around and it doesn't seem that anyone local rents bore scopes

I even called a machine shop and they guy told me: "I know some mechanics that have them, but they wouldn't rent them to their mothers, much less someone they don't know. They are too fragile and will break if you sneeze on them". :P

Can someone tell me exactly what sort of bore gauge/dial indicator to buy? I see a number on ebay...

And then what measurement am I looking for?

thanks!

[Ken A.]

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

Ian, I would put it all back together and set them at .012 / .018 and cruse on. It's pretty unlikely you have a 30/30 cam because if you did it would be a dog off idle until you got to 3000 RPM.

[Ian G.]

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

I am inclined to think it is the original cam as well, as the guy who rebuilt it (owned it two owners ago) said he didn't change the cam when he rebuilt it. The problem is I've never run the engine. I bought the car as a project.

What sort of sounds or "feel" could I expect if the valve lash is too tight vs too loose?

[Ian G.]

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

I have a dial indicator on order. Could someone kindly let me know what the lobe lift is for the other cams, so I can get an idea of what it is if it doesn't turn out to be the 283 duntov? And the Lobe lift is the value I'm looking for from the dial indicator right? I saw some other threads where Duke calculated it at the rocker as well...

CAM Rec. Duke Factory lobe clearance lobe lift inlet/exhaust
ramp heights

.008"/.018") (.008"/.012")
.030/.030) (.017"/.017")
.020/.025) (.012"/.017")

[Clem Z.]

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

I am inclined to think it is the original cam as well, as the guy who rebuilt it (owned it two owners ago) said he didn't change the cam when he rebuilt it. The problem is I've never run the engine. I bought the car as a project.

What sort of sounds or "feel" could I expect if the valve lash is too tight vs too loose?

noisy if too loose and won't idle if too tight. i would try .010 and .020 lash to start with and see what happens. that is the way i started out if i did not know the lash and changed it .004 at a time. post the lobe lift you get and we can see what cam comes close.

[Joe C.]

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

I have a dial indicator on order. Could someone kindly let me know what the lobe lift is for the other cams, so I can get an idea of what it is if it doesn't turn out to be the 283 duntov? And the Lobe lift is the value I'm looking for from the dial indicator right? I saw some other threads where Duke calculated it at the rocker as well...

CAM Rec. Duke Factory lobe clearance lobe lift inlet/exhaust
ramp heights
Duntov cam (283) (.010”/.016”) (.012"/.018") (.008"/.012") (.2625"/.2665")
Duntov cam (327) (.008”/.016”) (.008"/.018") (.008"/.012")
30-30 cam (.023”/.023”) (.030/.030) (.017"/.017")
LT-1 cam (.016”/.023”) (.020/.025) (.012"/.017")

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 TAPPET IS ON. I can not stress too highly, how important perfect alignment with the tappet 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.

[Clem Z.]

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.

here is what you need to measure the lobe lift. plugs right into the lifter bore

[Timothy B.]

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.