Retaining the cylinders on one side while assembling

[mike.smith]

Guess-timation is fine as long as one has some background or experience with a component in question. It is evident I wasn't clear enough in my statement that the published dimention was for a "STOCK" engine, and that it would be a "WORTHLESS VALUE" on a stroked engine such as the AeroVee. "I" wouldn't install the tubes without a given dimention, especially if it was my first build, any more than I would adjust the valves by "feel".

I'm still surprised there isn't a dimention to cover each possible incarnation of said AeroVee.

I still stand by my opinion that a published dimension for the pushrod tubes has little meaning. Too many variables. I've built an AeroVee 3 times and simply extending the bellows far enough to ensure compression when the heads go on, is all that has been needed. The dimension shown in Tom Wilson's book is 7-17/32 to 7-9/16"; a difference of 1/32"!! That's a laughable tolerance, especially since the bellows length WILL measure differently at every point around its circumference, simply because the bellows, being an accordion, will tip slightly one way or the other no matter how hard you try to keep it perpendicular to the pushrod tube body.

My suggestion is to worry about more important tolerances than the pushrod tube length, and simply extend the bellows so they require compression when the heads go on.

Tom's book also suggests you can add some Permatex to the seals before seating them in the case and the head. I don't believe that's part of the AeroVee assembly instructions, but from my experiences it's not a bad idea.

[wlarson861]

I'm with Mike Smith on this. The only thing that matters is that they are expanded longer than they need to be so that they compress when the head is torqued. Setting an exact length would mean they wont seal. The resistance to collapsing when the head bolts are torqued, holds the silicone seal tight against the head and case. If you need a starting point then put the heads on to the point the head seats on the cylinder and measure from the head to the case and add about 1/2 inch. Expand the tubes so that the length from the outer end of each bellows is at least that long. I have installed heads on this engine at least 4 times this summer alone and about a dozen times all told. I have simply expanded the tubes (by guess-ti-mate) to a little longer than needed and they have always sealed. Don't get caught up in paralysis of analysis but move forward.

[Area 51%]

And once again.......I haven't been able to make my point. It seems that there is a consensus that everyone who is assembling an AeroVee, or other stroked VW, has done it before. I'm not talking about a dimention that may or may not be measureable (1/32+-). I'm talking about what must be an obviously longer dimention due to barrel length (probably more like 1/2in). A starting point, to ensure the tubes are the correct ones for the build. A trusting "newbie" might not be able to tell the correct tension required by feel, or even question the lack of compression between the tube and seal.

As far as paralysis through analysis goes........if I just knee-jerked my way through this build, I would be the proud owner of a Waiex with a fuselage that is too narrow, a twisted glare-shield due to a malformed fuel tank, cracked factory formers, and a world of other imperfections that would have other builders rolling their eyes wondering what kind of idiot built this thing.

Can you elaborate as to why you had to remove and replace your heads 4 times this summer? Something missing in the instructions?

Thanks for staying through the credits from Area 51%

















5

[wlarson861]

Can you elaborate as to why you had to remove and replace your heads 4 times this summer? Something missing in the instructions?

At annual I found low compression in both front cylinders so I removed them and lapped the valves. Reinstalled them and they were improved but still below 60/80. Ordered new heads with the idea of rebuilding the old heads at a later date but getting in the air faster. Installed new "MOfoco" heads and they had defective spark plug hole that stripped prior to getting full torque. Sent back to Sonex for replacement. Installed replacements and during ground run detected leak in right rear cylinder, found cracked and burned cylinder in the combustion chamber. Replaced cylinder and reinstalled head. hopefully for the last time for a while.

As far as the correct tubes go there is only one and they are all the same size when new. No matter what source you get stock vw push rod tubes from they are all the same size, too short and need to be expanded. If you get the spring loaded type they will be too long and need to be compressed on installation. The method to fit the tubes that Mike Smith and I have laid out is the method used by every vw builder I have heard of. I questioned the method in my mind when I built the engine new but followed instructions from other builders and it was fine.

[SonexN76ET]

Area 51, I mean no disrespect here, but engine building is not for everyone. This is a decision that only you can make. There are far more important things to consider in building an engine than the items you have inquired about. You may want to consider getting some assistance from a skilled engine builder. There is nothing wrong with getting a little help. People get help with paint, avionics, and upholstery. Why not get help with the engine? Especially if there are things about the assembly you are unsure of. The engine is far more critical. Your life and the life of your passenger will depend on it. I could have used some skilled help on my engine build. Had I done so I would have saved a couple of grand on unnecessary repairs due to my own errors.

Thanks,

Jake

[gammaxy]

Area 51,

I used 7 9/16 as measured between the outside ribs of each pushrod tube. I got this number from How To Rebuild Your Volkswagen Aircooled Engine. I didn't apply anything to the seals and after 200+ hours haven't had any noticeable leaks from the tubes. I only used the copper gaskets and no barrel shims on my engine.

I honestly don't understand why 7 9/16 worked for me despite the longer stroke of the Aerovee engine.

I think your estimate that it should be 1/2 inch longer is due to the Aerovee's stroke being 13mm (~1/2 inch) longer than the 69mm stroke on the ~1600cc stock engine. I believe you should only expect half this amount, though, since the piston will only be 6.5mm higher at top dead center (and 6.5mm lower at the bottom of the stroke). So, 7 9/16 + 1/4" seems like it might be reasonable, but from my experience 7 9/16 seems like enough.