When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So I have the Comp Cams 7702 pushrod length checker. Went through the whole measurement technique. I understand all of that just fine. The question I have relates to the actual dimensions of the checker.
Closed it is supposed to be 6.800", but when I measure it with calipers, it measures 6.815". (I have 2 of the 7702,and the both measure the same - 6.815")
And... Therefore, when I find the perfect length pushrod to give me zero lash, by calipers, it measures 7.755". But when I count turns, it is 18.8 turns which calculates out to 7.740" so which is the correct pushrod length? (yes, I know we are only talking about 0.015", but in some cases that would make a difference in pushrod choice)
Ideally you would actually want to measure with an actual pushrod so you know exactly what you are getting into for clearances and also length. That is how we do it here and we just have boxes of one off pushrods so we can make sure what we get for each engine is correct. Now the home mechanic that only does this a few times, that wouldn't make sense.....so
Different manufacturers do lengths different....which I know is odd but they do. So you could have three different lengths all for the same pushrod.
I would say measure the actual length and talk to who ever you want to get the pushrods from and see how their parts stack up. Some will tell you to measure and they will figure it for you, others will say count the turns from what is on the checker and add 0.050 to it...just depends on who's checker you are using and what company you are getting the pushrods from.
vettenuts left this explanation over on the C5 side too. Gauge length makes perfect sense. Thanks for the replies.
Originally Posted by vettenuts
The difference is the measurement methods you are using. Using the turns of the pushrod is done because the pushrod is measuring "gauge length". Gauge length is the distance between the two ball ends where the ball is 0.140" in diameter. This point on the ball end (0.140" diameter) is impossible to find with a caliper and that is why they count turns. You are measuring "Overall Length" with the caliper, which is the distance between the ends of the *****. Trend (who makes most of the aftermarket pushrods for other vendors such as Comp) doesn't believe this is accurate since this measurement is very sensitive to the way the ball is machined into the end of the pushrod therefore they use gauge length. Manton, on the other hand, uses overall length.
The difference between gauge length and overall length is typically 0.013" - 0.017" so your difference of 0.015" is right in the middle. In essence the pushrod measurements you are taking are the same length when you account for the type of measurement you are taking.
Note also, the tolerance on length is typically 0.005" so even if all your pushrods are 7.400" there might be some variance in length between them.
Pushrod Length Checker Questions
