Everywhere Ive read says my 429 Thunderjet should have 8.55 pushrods. Or 8.67. Mine measure out to be 8.642 using a precision micrometer.

So 8.67 is a go yes?

I have no guide plates and non adjustable rockers.

Can I swap to 3/8 pushrods with no modifications? 5/16 are spindly for a big block.

 

To do it right you should get a pushrod checker and adjust to 0 lash. Then add 0.030” to your checker length.

 

there's no adjustment for lash. So just torque to spec?

 

Yes. Your adjuster will find 0 lash. Add 0.030 for plunger compression.

buy pushrods of adjuster length plus 0.030”.

 

You need to read Adjusting Hydraulic Valve-Train in the correct year FORD SHOP MANUAL.

Why do you feel you need to adjust them, recent valve-train work?

 

The engine in question is in a 71 thunderbird. Trying to get it running. Has two bent pushrods. I think they were the wrong length and I want to get the right ones to replace them.

 

If the engine has been setting quite awhile it may have a stuck valve.

 

At least 2 judging by the 2 bent pushrods.

both intakes, on 4 and 7.

 

You should be able to bring each cylinder around to the base circle on the cam and push the valves down to see if they're moving freely.

As you've been told the only way to know what rod length you need is to check it. once you determine the length you need if an off the shelf length won't work someone like Smith Brothers will make you a custom set. this is a normal part of rebuilding and engine if you don't have adjustable rockers.

 

The adjustment on an hydraulic valve-train (non-adjustable) is accomplished with differing length push-rods. Even something as simple as a valve job may upset the geometry. Do you have a FORD SHOP MANUAL for the engine? It will give you the service push-rod length(s) and description of how to adjust.

 

Just a word of caution that no one mentioned yet.....

The 1971 429 should be the standard or more common pushrod length....the 8.55 inch

The 1968 first year 429 used the .100 longer length design (the 8.65 length for the C8VE HEAD) as the lifters are different application also, so beware.

I found that out the easy way needing a pushrod for my 1970 Thunderbird as I grabbed a pushrod from the 1968 Thunderbird engine and noticed the discrepancy back in 1985....

I still have my 1968 block and C8VE heads onhand !...along with the longer 8.65 pushrods too.

I still have my 1970 Thunderbird to this day too - now you all know my basis of the "silvereagle" name.

 

what changed from 68 to 71?
I have afaik a 71 block amd d0ve-c heads. And pushrods that measured the mentioned 8.642. They are worn so maybe they were 8.65.

 

I wish I could help you further but my old computer is in ICU and I don't have access to the TECH INFO I once had. You can buy a replacement rod from a vendor such as NAPA to use to check correct valve-train geometry. You would then replace as needed to get the correct valve lash.

 

As I mentioned in my previous post :
The 1971 429 should be the standard or more common pushrod length....the 8.55 inch
The 1968 first year 429 used the .100 longer length design (the 8.65 length for the C8VE HEAD)

What changed was the length of the 8.65 inch pushrod after 1968 .....

As far as I know, All 429's for 1969 (C9VE-A) and later installed the standard 8.55 inch pushrod, which many parts aftermarket applications will only show one application and include the 1968 model year....

I had a #2 intake rocker go loose on my 1970 429 one day, nursed the car home as I seen the pushrod slightly bent - so I went to replace it with pulling a pushrod off the 1968 Thunderbird 429 engine (family car that sat) and after installing it on the 1970 engine's #2 intake rocker - it would not rotate freely and felt tight.

I pulled another straight pushrod off the 1968 engine and the #2 exhaust pushrod off my 1970 engine and noticed they were different lengths and taken them both to a NAPA parts store back in 1985 for some insight - as one counter person told me the longer pushrod is for a 1968 application when I inquired about it, and I believe the 1968 lifter application is also different to match the 8.65 pushrod application - if not, then the 1968 rocker arms would have to be a different application (which I doubt it)..... I purchased the last four 8.55 pushrods they had in stock so I would have more onhand.

Installed one of the new 8.55 pushrods in the #2 intake position and felt right, rotated freely with valve closed, and I was back in business with no issues.

Maybe the parts guru Number Dummy can shed some light on the official word on what his books show on valve train parts for a 1968 year 429, and what may have inspired and changed for 1969 and later......why the pushrod lengths were changed is beyond me as my 1968 429 engine had no issues when it was driven.

I will go out on a limb and speculate :

1 - I still say that the 1971 429 engine had original factory length 8.55 inch pushrods...(as stated that the cylinder heads on this engine do show D0VE-C casting)...The two pictures shown seem to look as if everything is very original (and engine dry and not ran in a while)
2 - Someone might have replaced some or all of the pushrods with the longer 8.65 length ones...(I would compare every good pushrod left in that engine and verify the length)
3 - Unless the lifters were seized, collapsed, stuck valve as mentioned, etc. - I wonder what other reason why those #4 and #7 intake pushrods were bent....could it also be the wrong longer pushrod application ?.

All stock 429's have the 5/16ths diameter pushrods.

IF - this particular 1971 engine came with factory 8.65 length pushrods, that would be a first to my knowledge...I have never ran into any other 429 I have ever worked on or scrapped out that had any 8.65 length pushrods, other than my 1968 year with C8VE-A cylinder heads.

 

None of this really matters, it's not about what length it came with it's what length do you need now. if the block has been decked, heads shaved or who knows what things have changed.

If you want it right you have to measure it .