Push Rod Length

[pilotyoung]

After an oil change a couple of weeks ago, I was adjusting the valves in my AeroVee 2.1 engine. When I got to the number one cylinder, I could not get a feeler gauge between the rocker arm and the valve stem. I had adjuster the valves 27 hours before with no problem. I did not notice the last time I adjuster the valves that the adjusting bolt on the rocker arm was all the way out. So after getting advice from some Sonex owners and talking to Kerry at Sonex, I took the heads off. The number one head had a crack between the two valves and the valve seat had receded into the head. So I ordered two new heads from Sonex and installed them. When I started adjusting the valves, the number three intake valve adjusting bolt was almost al the way out when it was adjuster. That didn't seem right to me when al the other valve adjusting bolts had about a 1/4 inch of space available for further adjusting. Kerry had told me that the valve probable failed because of excess heat or the push rods might not be the correct length. So after noticing the situation with the number 3 intake valve, I decided to check the length of the push rods.

I used the push rod length tool and set it up as specified in the manual. When everything is set up correctly and the push rod length tool is adjusted as short as possible. it is too long. At the minimum length it pushes the valve in instead of just touching it.

So I called Kerry again and while he was helpful, as he always is, he said some people have to cut the push rod adjusting tool to a shorter length. I ask why and he said he did not have an answer. He said there are so many variables for him to give me an answer. I borrowed the push rod length tool from a friend who used it and it worked fine for him, it was not at the minimum length for his engine. So it just does not seem right to me that everything can be right in my engine and I have to cut the push rod length tool.

My engine is set up at 8.1 compression ratio and there are two shims under the rocker arm supports. I have a new set of push rods if I need them.

Has anyone else experienced this? If so, was there a problem with your engine? Anyone have any advice or suggestions?

[GraemeSmith]

As you changed the heads - did you check and reshim the rocker set?

In addition to getting the rockers to contact the valve stems a hair off center so the valves rotate, a tiny change in the height of the rocker set makes a difference to pushrod length.

And the heads may have had a slight different height too.

[kmacht]

Here’s the problem. The aerovee kit is not much more than a bunch of aftermarket VW parts that are put together and sold as a kit. The aerovee manual assumes that every part they supply is exactly the same. This is about as far from the truth as it gets. I found all sorts of issues when building my aerovee where part tolerances and variation made a big impact on having a reliable engine yet the aerovee manual had you check none of them. Some of the things I found were the oil pump output hole not lining up with the case hole (about half of it was covered, camshaft endplay was way off from spec because the cam bearing didn’t seat quite right in the case, the two heads cc’s were different enough that had I just used the chart in the aerovee manual I would have ended up with two cylinders with a compression ratio of 7.5 and the other two at almost 9. The point is that there is a lot more to putting together a reliable and well running vw engine than just slapping a bunch of parts together and assuming they all work well together right out of the box. You are seeing this where your pushrods are significantly different than what your old head used. Before cutting new pushrods I highly recommend cc’ing the heads, remeasuring the piston to top of the jug clearance and calculating the actual compression ratio based on something other than the aerovee manual. You may need more barrel shims or a copper gasket on the head to get it right. After that read up on be rocker arm geometry so you use the right number of square shims under the rocker shaft blocks and the right number of round washers to get the correct angle on the swivel feet where they push on the valves. After that then cut your pushrod tubes. An aerovee can be built and run right out of the box but you need to know what to look for and how to adjust if parts aren’t exactly to nominal spec.

[BRS]

Here’s the problem. The aerovee kit is not much more than a bunch of aftermarket VW parts that are put together and sold as a kit. ...... An aerovee can be built and run right out of the box but you need to know what to look for and how to adjust if parts aren’t exactly to nominal spec.

... and that is why I ordered a RevMaster.