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fergerburger
19th October 2009, 07:45
I'm tearing down the 75 to replace the cases. I could not get the exhaust pushrods out without removing the heads. I collapsed the lifter adjuster all the way but there was not enough clearance to get the rods out. Intakes came out okay. I wonder if this is a valve issue with the valve step height out of whack?

Anyone had problems like this? I recall I had to fool around with my 74 front exhaust adjuster before I finally got the clearnace i needed to pull the push rod and replace the seal. I tried eveything but both the rear and front exhaust pushrods just could not get clearance to come out.

Hopper
19th October 2009, 10:07
Possibly the valve seats have been cut too deep, seating the exhaust valve too deep, causing rocker arm to be canted up on the valve end, down on the pushrod end.

Factory manual gives the dimension to measure from the collar on the valve guide to the tip of the valve stem, so you can soon see if the seat is cut too deep. (Note the measurement is from the collar on the guide, not right from the head itself, the diagram is a bit small and hard to see this detail.)

Hardened seat inserts for modern gas would soon fix it, if the seats do measure up too deep.

fergerburger
19th October 2009, 21:57
Yeah, that's what I'm thinking. Most valve jobs I've done on cars require some butt-grinding to get the stem height right. I'm surprised no one else has had this problem.

Jafa39
19th October 2009, 22:01
That must mean a heap of seat recession....there was acres of clearance when I last pulled my 73 apart.

madfox22
19th October 2009, 22:19
Yep. Valves stuck too far into head. When you perform a valve job on these heads, your goal should be to acheive an installed valve stem height of 1.375 to 1.420 from the top of the valve guide flange to the top of the valve stem. You will not have any problem with removing or installing pushrods in this range.
If you are a little above the 1.420, you can surface a small amount off of the stem to get within the range, but too much ground off here will cause the curve of the rocker arm to interfer with the valve spring retainer ! You don't want to pop the keepers out while the motor is running! Ouch
I have, at times, had a reading of 1.450, and cut between .030 and .040 off of the top of the stem without a problem. More than that may be dangerous.
Valve stem height is also important when trying to acheive the proper valve spring installed height.

fergerburger
30th October 2009, 01:31
I pulled my heads and checked the stem height. It was 1.420 so I'm not sure why my pushrod would not collapse. This may be an issue when I put that motor back together. Has anyone else had an issue with collapsing their exhaust pushrods. I verified the tappet was collapsed all the way.

IronMick
30th October 2009, 03:46
I ... checked the stem height. It was 1.420 ...

The 1.420 spec is in the "Service Wear Limits" section of the Specifications. Does this mean it is at the end of its usefulness? How do the valves look re being sunken into the seats?

fdny37
30th October 2009, 05:17
I have the same problem on my stroker with the exhaust valves. I now use the Andrews chrome moly pushrods which are made shorter just for this reason. I was told by my engine builder that this is not an uncommon problem with exhaust pushrods.

fergerburger
30th October 2009, 07:18
The valves do look recessed far into the head. The rear exhaust height is like 1.70 so it is way out there...the heads look like they were redone by a complete hack as all the guides look to be different. some of the guides have no collar and are not set into the head the same depth. seems real odd to me. I should post pics

madfox22
30th October 2009, 15:10
When rebuilding the heads, the valve stem height you are looking to achieve is 1.375 to 1.420. More then the 1.420 is OK, its just that you start having problems with the pushrods clearing the tappet ball sockets when you try and remove them.
I have rebuilt some heads and had to face the tops of the stems slightly in order to achieve the max 1.420 but even then you cant take much off of the top of the stem without the rocker arm interfering with the upper spring collar.
I admit, sometimes I have left the valve stem height a little over the max.
1.7 is more than a 1/4 inch over that limit and would be considered too much.

madfox22
30th October 2009, 15:15
The valves do look recessed far into the head. The rear exhaust height is like 1.70 so it is way out there...the heads look like they were redone by a complete hack as all the guides look to be different. some of the guides have no collar and are not set into the head the same depth. seems real odd to me. I should post pics

No collar ? Ya talking about the lower spring collar? Gotta have one to avoid spring walk, and to get the proper spring tensions.
Yeah, ya oughta post some pics so we can see what has been done to these heads and help you with your problem.

fergerburger
30th October 2009, 17:06
I've got to post pics of these heads/guides. There is no collar or flange at the base of two of the guides. It's odd to me that the stem height is measured from the guide flange and not the head itself. If there is no flange on the guide, then where do you make this measurement?

madfox22
30th October 2009, 20:13
The correct guides are supposed to have the flange on them so that when you install them while the head is hot (best to warm up the head when installing guides), they will stop in the correct position. However, I have seen and used straight guides before.
What you have to know is the thickness of the flange on a stock guide, then subtract that amount from your measurement. I don't have one in front of me right know, but best I remember they are .090 thick. If your valve stem height measurment is 1.700, and you subtract the .090, the installed height is 1.610 (too much)