Push rod size?
Thread Starter
Former Vendor
Joined: Mar 2003
Posts: 18,666
Likes: 395
From: Tampa FL
St. Jude Donor '07-'08-'09-'10-'11-'12'-'13-'14-'15
Push rod size?
I am running stock 7.4 chromoly PRs but have heard some talk about using slightly differing lengths depending on combo. I have AFR 205s milled to 59cc, .040 cometic gasket and 228/232 .588/ .595 114 XER cam. Any idea if I need to change lengths? I ask because the car makes some very loud "sewing machine" noise and I have heard this may be a contributor? Thanks
Cajun
Cajun
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
You removed about 0.056" from the pushrod length with the milling and the gasket. I would measure to make sure, but you will get some sewing machine sound with an aggressive cam lobe, it will sound "well oiled" though, not a "tick tick". (Not sure if that makes sense).
Side question, what did you do to prepare your block for the Cometics other than cleaning it real well?
Side question, what did you do to prepare your block for the Cometics other than cleaning it real well?
Thread Starter
Former Vendor
Joined: Mar 2003
Posts: 18,666
Likes: 395
From: Tampa FL
St. Jude Donor '07-'08-'09-'10-'11-'12'-'13-'14-'15
You removed about 0.056" from the pushrod length with the milling and the gasket. I would measure to make sure, but you will get some sewing machine sound with an aggressive cam lobe, it will sound "well oiled" though, not a "tick tick". (Not sure if that makes sense).
Side question, what did you do to prepare your block for the Cometics other than cleaning it real well?
Side question, what did you do to prepare your block for the Cometics other than cleaning it real well?
Cajun
Safety Car
Joined: Sep 2003
Posts: 3,558
Likes: 2
From: Cape Coral FL
You need to check your preload and valve tip wipe. With hydraulic lifters preload isn't as critical as solid rollers, however, if the preload is more than .100" and less than .060" you mprobably should change pr length. Tip wipe is something that should be paid attention to more. If you don't have a narrow and centered wipe pattern you will be losing lift, power, wearing valve guides out quicker, and it also may be a contributor to excessive noise.
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Preload is a function of valve height, rocker arm position, lifter operating height, pushrod length, and cam base circle diameter. The easiest way to detrmine the optimum preload is to use a checker pushrod to find your zero lash point, then select a pushrod that will give you that length plus your desired preload. On a h/c car with moly pr's .080" seems to be the most recommended preload.
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Preload is a function of valve height, rocker arm position, lifter operating height, pushrod length, and cam base circle diameter. The easiest way to detrmine the optimum preload is to use a checker pushrod to find your zero lash point, then select a pushrod that will give you that length plus your desired preload. On a h/c car with moly pr's .080" seems to be the most recommended preload.
Last edited by ArKay99; Oct 16, 2007 at 10:30 AM.
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
You really need to measure and as stated in the prior post, check your wipe pattern as well. You should do wipe first then pushrod length with a non-adjustable rocker.
Le Mans Master
Joined: Aug 2003
Posts: 9,298
Likes: 4
From: American Canyon Lethal Injection
Cajun..do it right and get the Comp push rod checker to get the proper length needed. I chased around trying different size p-rods trying to get the right size to quieten the sewing machine sound.
