valve lift loss?

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
john rod
New Member
New Member
Posts: 8
Joined: Thu Sep 20, 2012 2:39 pm

valve lift loss?

Post by john rod » Thu Aug 10, 2017 8:34 pm

RE: SBC 292 heads, I had a set of new valve guides put in sometime back. I am short on lift about .023 Inch. [to be truthful-I dont remember how close the lift was before-so old age doesnt help here!]. anyway, I have measured a lot of different things. including checking the rockers on a totally different engine-rocker ratio is dead on 1.6. the block was milled .015, and the heads .019. in order to get the rocker tip in the middle of the stem, I have to use a 100 long pushrod. that doesnt sound right. the rocker is tipped a lot towards the valve. seems like a .050 short pushrod would be closer to correct. yet, using a 50 short pushrod looses more lift even. I am now wondering, what if the guides were put in on a different angle, let's say 21 degrees [for the sake of argument] that would kill off a lot of lift, correct? now let's say that was true, how the heck do you correct that problem?
any help, ideas, speculation or accurate correction will be greatly appreciated. :evil:
thanks, Rod in AZ

tenxal
Pro
Pro
Posts: 375
Joined: Sun Nov 17, 2013 8:48 pm

Re: valve lift loss?

Post by tenxal » Thu Aug 10, 2017 10:21 pm

Have you checked the lift at the lifter?

CharlieB53
Member
Member
Posts: 149
Joined: Fri Nov 22, 2013 2:44 pm
Location: Wright City, Missouri

Re: valve lift loss?

Post by CharlieB53 » Thu Aug 10, 2017 10:54 pm

When the guides were installed was the guide to top spring collar clearance checked?

This is a very common error, having the collar collide with the guide, limiting opening, causing pushrods to 'flex'.

mag2555
Guru
Guru
Posts: 2121
Joined: Sun Sep 18, 2011 11:31 am

Re: valve lift loss?

Post by mag2555 » Fri Aug 11, 2017 6:21 am

If on a 23 degree Head the valve inclination angle was shifted to 21 degrees I don't think you would be able to cut or grind a valve seat back into the chamber!

Geoff2
Expert
Expert
Posts: 620
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: valve lift loss?

Post by Geoff2 » Fri Aug 11, 2017 6:22 am

A 21 degree [ or less than 23 ] angle would increase lift, not decrease lift, all else being equal.

Ericnova
Member
Member
Posts: 77
Joined: Tue Jan 01, 2008 2:56 am
Location: Southern Michigan

Re: valve lift loss?

Post by Ericnova » Fri Aug 11, 2017 3:57 pm

Your emphasis on getting the rocker tip in the center of the valve tip is the big misguiding problem here......that's not how valvetrain geometry and finding correct pushrod length is done correctly..

Watch this video to learn a correct method.....tech video is from a member here....

https://www.youtube.com/watch?v=o5is9Bs ... e=youtu.be

Your lift loss is likely because you still don't have a long enough pushrod in it yet.

Post Reply