Valve Lift 4

[scuffedup]

Good Morning

I need to check total valve lift on some racecar engines. I understand how to check lift with a dial indicator but there are varying opinions on this method being acurate. My fixture will screw directly into the rocker cover mounting holes, so I would not have a problem with the magnetic base moving.

The reason I need to check this at the valve is the rule states "maximum .500 lift at the valve. So a cam ground for lets say 498 lift with a 1.5 ratio rocker arm would go over the maximum with a 1.6. Obtaining rocker arm ratio can be time consuming to do acuratley.

I need to be able to check this after a saturday night race with some sharp engine builders looking on so I want to be fair and acurate.

Any help would be appreciated.

Thanks

 

[thundair]

.500 valve lift with a 1.5 rocker ratio is .333 on the cam or am I missing something..

Cheers

I don't know anything but the people that do.

 

[scuffedup]

Yes I understand this. I am trying to make sure that checking lift at the top of valve spring is accurate. The cam and rocker ratio will be unknown and the engine together. This is for tech at a race track.

Thanks

 

[FoMoCoMoFo]

that will work if done correctly. cam and rocker ratio are irrelevant. but lifter bleed down could be an issue. good luck.

 

[Tmoose]

Valves move in essntially straight lines, so unless the retainer cocks or tips the retainer motion will equal valve lift. The indicator stem should be parallel to the valve stem to reduce angular errors, but also to avoid errors introduced by retainers with angled or beveled top surfaces. Best to hit a surface perpendicular to the valve CL if one exists.

http://www.flatlanderracing.com/imagesgraphics/comp-titretainers.gif

 

[scuffedup]

Thanks. I was looking for support I guess. Engine builders are gonna try to discredit my procedures if my findings are not in their favor.

 

[patprimmer]

Are they solid lifter or hydraulic.

As previously mentioned hydraulic bleed down can be a problem.

I would check more than one cylinder as astute racers might leave #1 legal, but cheat on the rest.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[scuffedup]

Yes they are hydraulic lifters. I thought about lifter bleed down but I don't think that would be much of a concern because if they were bleeding down much there would be valve clatter upon start up.

I think I am going to build a jig to measure rocker arm ratio so that if someone bucks on my test procedure I can measure at the lifter and do the math.

Thanks for all the help. You folks are great.

 

[patprimmer]

You could use an adjustable pushrod to Bleed the follower down then measure at zero tappet clearance.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[robert1612]

If you use rocker ratio method: I have 2 gutted hydraulic lifters pressed together with an aluminum rod in center (top to top). Make sure you surface the upper lifter flat, then put my dial indicator (with extension) onto the second lifter face to degree cams. Makes a nice big indicator surface.
If room into lifter galley is hard to obtain for this method or you want the 'all inclucive' measurement. Use the current push rods and rockers, replace the race valve springs with test springs of about 10lb force so the lifters do not bleed down during the check. Mount magnetic dial indicator to flat stock attached to valve cover bolt holes. This way ALL the valve train parts and hard to calculate angles are included. Remember in all the math you attempt to use for rocker arm ratio, the contact point on the tip of the rocker changes the ratio (roller rockers excluded) as it sweeps the valve stem. Effective measurement point will move approx 1/4" depending on cam lift and several other 'circular relationships'.

 

[patprimmer]

Some problems with the rocker ratio method are that on some rocker types, the effective fulcrum moves with rocker action.

With all types the effective ratio changes as the valve and the pushrod may not both be perpendicular to the axis of the rocker arm at mid lift.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[scuffedup]

All inclusive is what I have in mind, ad thats a great idea. Would a test spring center the lifter in the bore or should we just take it to zero lash?

 

[FoMoCoMoFo]

The test spring is a good idea. but if I'm a racer and you start making adjustments to a rocker,or install an adjustable pushrod I'm going to cry foul. I think you just have to hope you don't find lash. or? good luck.

 

[scuffedup]

Agreed. Thats why I let them do the work and I just measure.

 

[IceStationZebra]

I agree with the test spring idea. It measures all of the as run parts in the engine. You can not do much better than that! You could also take it a step further and measure the valve angle with the spring off to make sure they did not angle mill the head or rebore the valve guide.

Have fun screwing the air chuck into the still smokin hot race engine to keep the valve from dropping

ISZ

 

[scuffedup]

LOL smoking hot engines is what makes my job so fun!

But in real life I have the same obstacles but alot more stuff in the way. So the racecar engines are alot more fun.

Thanks for the help.

 

[NormPeterson]

Can an adjustable pushrod be fabbed such that it registers off the OD of the lifter instead of from in the normal pushrod socket? Wouldn't matter what kind of lifter was there and would only require the removal/replacement of the rocker arm(s).


Norm