db8

db8

Well Known Member
Had a crack in my Lycoming engine case. Swapped it out with a new Superior case with roller tappets. The guys at Superior said the pushrods I have should work fine. We put them in, but it took some pushing on the valve springs to get the rocker arm pins in. The spring hydraulic lifters were bled. I was using eight of the -35 pushrods. The only size below this (shorter) are the -34s. I got some today in Cincinatti and I am having the same problem. The -34s are the smallest they make. I know the rocker arms can be grinded down some with a special grinder, but I'm not sure that is the proper solution.

So, I'm just wondering why the difference if Superior says there shouldn't be? How am I going to get to the .028 - .080 gap having the smallest pushrods they make. I have tried swapping some around a little because I know their lengths vary some?

Any thoughts or insight would be appreciated. Thanks. Dave
 
Only comment is to make sure the lifters are bled all the way down, and kept that way, when you measure the gap.
 
Yes

That has been done --all the way down. I went back and bled them again thinking they weren't bled enough or something....but still the same problem. Thanks. Dave
 
Also make sure that the tappet you are checking is on the "bottom" of the cam lobe.
I know this is elementary, but you never know.

If you need more clearance, you can shorten the pushrod, but please do NOT grind the rocker arm.
 
Thanks

Thanks a bunch Mike. You made my day (less stressful) knowing there's an easy solution. I thought there had to be. Dave
 
I have 8 -31s that came out of my group B cylinders that I was not able to reuse when I replace them (had to go with -34s on the new cylinders). PM if interested.

Dan
 
I had exactly the same problem, I was scratching my head then spoke to the engine shop and realised that....

Even though the cylinder is at top dead centre, if its on the exhaust stroke there is a fair bit of valve overlap so one or both lifters may be slightly lifting. You need to be on the compression stroke at TDC to ensure both lifters are on the heel of the lobe.

Hope that makes sense.
 
Breaking it down in simpler terms, I can turn the crank and watch (as an example) the number 2 exhaust pushrod go out then in, then the number 2 intake pushrod go out then in. Then the two pushrods will be in and this is where/when the place to measure the gap? That's the simplest, non-technical way to break it down (I believe)?
 
I have a pushrod I made out of an old one that has an adjuster screw. I use this to set the dry tappet clearance then take it out and measure the length with a long digital caliper to determine the right pushrod. Takes all of the guesswork out of which length of pushrod to use. On my engines I now have adjustable roller rockers I had made which eliminate the problem alltogether...only one length of pushrod necessary.
 
Neat Bob -- good idea

Some guys around the hangar were wondering the best way to determine the pushrod length required. When I built the engine the first time (actually I was fed all the information from the A/I as we did it together), he had a bazillion pushrods that we just kept swapping out till we got a middle reading between .028 and .080.

He has since passed away and I have no access to the different size pushrods. Would be neat to have a "sampler pack" or something of the different sizes. Was thinking of a wooden dowl rod too. The adjustable one seems like a great idea Bob -- might have to make one. I sure hope I won't need one very soon after this. One would need a pretty long caliper to measure (as you mentioned). Where would you find something like that?
 
db8 said:
Breaking it down in simpler terms, I can turn the crank and watch (as an example) the number 2 exhaust pushrod go out then in, then the number 2 intake pushrod go out then in. Then the two pushrods will be in and this is where/when the place to measure the gap? That's the simplest, non-technical way to break it down (I believe)?
Click to expand...

Look through the spark plug hole and turn the prop backwards while the pushrods are in. As the cylinder comes up to TDC, both pushrods should be retracted and not moving around TDC, you are on the compression stroke.

If you come up to TDC and notice pushrod is moving and before it stops moving the other moves that is valve overlap and you are on the exhaust stroke and will be on the lobe of the cam.

After you have found TDC on the compression stroke, remove and bleed the lifters down for that cylinder then reassemble and measure the tappet clearance.

If you've not done it before, best to get someone who has to show you on one before you tackle the rest.
 
Thanks for all of the posts. The gentleman at Superior (not Bill the main tech), apologized for the misinformation. The roller tappet push rods are shorter (as most of you have pointed out).

Superior sent me 3 samples of different lengths and the -31s give me the .028-.080 gap I need. That was very nice of them to do.

I have been very happy with Superior and their help/customer service on this case swap.

Dave
 
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