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"Best"? exhaust valve guide material?

Okay fine there Zippy.....:icon_bs:
"There is absolutely no way"
Lovely how you are so "absolute" in your reprimanding me.
The requirements are 100% power for 5 minutes, and 75% for the duration of the flight.
Zippy? There is nothing I stated that is not true. I do not dispute those requirements. I will repeat that a type 1 VW motor is not up to those requirements. There are engines designed for that level of service and that VW motor is not.
 
An airplane engine would have to use the authorized repair parts because they are the ones that have been tested and approved. They are likely a balance between the very best, and good enough to function for the number of hours between the regulated cycles/time between maintenance events.

Catastrophic failure can't be tolerated but would likely occur if the engine was taken off the maintenance events schedule, and just subject to continued use until components wore out.

Because of cost-based, and time-life selection the recommended ones may not be the very best. Using the engine outside of airplane use race car engine parts may be the better selection. A pro race engine rebuilder/designer might give the best advice
 
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I am basing my answer in what I know works in Harley engines. When the lead was removed from gas, Harleys started having all kinds of valve/guide problems especially sticking valves. The cure was found to be fine grained cast iron guides with nitrided stainless valves with valve guide seals.. The upside to this was tighter clearances and much longer life, like at least 4 times what it was previously! You see almost no valve stem or guide wear even with high miles. I would think a VW could benefit from this?
 
I found Thesamba, lots of machinists there with knowledge of machining VW engines.
With that information, i made tooling and a fixture

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I thought my engine guru was dodging me, after over a week of non-committal responses. He sent an email with enthusiasm for the project.. Valves and such were ordered mid-last week, hope to see them soon. Guide decisions are still up in the air until we meet to discuss this, and whether any OS dia are needed. One that was removed started spinning before the counterbore was as deep as i'd like; and it is discolored a little partway up the OD above the end that extends into the chamber. In pinch, though, the fixtures and tooling are now on hand if something conspires to force me to complete the heads here including boring for OS guides, or seats. I hope not. :)
 

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what valves did you opt for? ev4? ev8?

edit: "thesamba" is interessting. i used to hang out on "914world".
 
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stainless get the most votes, especially on the aircraft forums.
Apparently (as alluded to earlier this thread) for VW aero engines, valve jobs and valves are a 200 - 250 hour routine maintenance Item, and you just use them as consumables. It all seems cheap compared to Lycoming and Continental parts, but a regular (pun intended) nuisance. If these heads were not refreshed when the nikasil cylinders were removed and steel barrels installed & logged as "moteur neuf" then they are right on schedule with something around 300 hrs. I would hate to think they were fresh, have this much wear on the exhausts, and were new 33 hrs ago at that log entry.

Hard chrome stems get a lot of support, it's not uncommon for airplanes. But i went with plain. In some of my reading, it appears VW actually used to make sodium filled valves. I did not explore that.

As mentioned, i'll run this all by my engine guy who is also a pilot.

smt
 
Gad's, shocking to notice that in a couple days this will be exactly one year later..
Adding on here since the info could be relevant to anyone else interested.

It is almost religious wars on the VW forums:
Keepers are supplied/or factory valve stems ground as new, such that when the keepers are in the retainer, the EX valve is still somewhat loose in the keepers and can be rotated.

Apparently VW thought this was a good idea, and some head manufacturers still do and say so on forums even for performance engines. An awful lot of builders say "grind the faces so they cannot touch, so the keeper grips the valve stem like a collet"

My valves are Manley Stainless, keepers were supplied with them.
When tight in the retainer, the EX valve is snug but can be rotated.
Old stainless valves removed from engine rotated.

I am aware that (often, not always) valves rotate anyway from vibration & from spring torsion.

Nonetheless, which is a better idea in an aircooled boxer VW engine: install keepers as supplied, leaving stem loose as factory practice?
Or grind the keeper faces so they grab the stem like a collet?

Please let fly with the opinions. :)

smt
 
I'd still go with titanium. Yes, more expensive but not that much - and if they are that much, easy to make even in a South Bend.

I'd even do the scallopy thing. Yes you aren't turning a lot of revs but if you reduce the weight 20% (ti is 5/8 the weight of steel but you have to count the valve in the recip weight as well), then you reduce loads even more. But let's just say 20% ... so that's 20% less load on the pushrods, so they track more accurately. Valve timing is better. 20% less load on the followers and the cam, so they last longer. Less load on the timing gears, so they don't wear out as fast. And it's just as dependable as steel, not like the aluminum collars.

Some racy stuff like carillo rods and so on is definitely not worth it but for this purpose, I'd go titanium.

Or, depending on the glide ratio of your homebuilt, maybe I'd go carillo as well :D
 
To the point of your post, it ain't hardly ever the rods fail.
Not infrequently a valve issue.
Or a broken forged crank sometimes with heavy props due to resonance issues.
Although across GA, experimental and spam cans both, still some 50% of incidents caused by a lack of pleasant steady noise from the engine bay is down to lack of fuel in the tanks......

So, what spec for Ti?
can you copy essential dimensions from steel part? Or do sections have to be larger?
IIUC Ti is notch sensitive, so round corners/transitions, etc. ?

Is this a better bet that scalloping the steel retainers? Probably 15 - 20% there and easier.
 
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To the point of your post, it ain't hardly ever the rods fail.
I was joking about the carillos. Altho .... if it wuz me up there in the sky, I'd probably consider it, just in case :)

So, what spec for Ti?
can you copy essential dimensions from steel part? Or do sections have to be larger?
IIUC Ti is notch sensitive, so round corners/transitions, etc. ?
I did a bunch for a cam company, they were 6Al4V, no burrs (but I always roll around the corners and never make burrs), the biggest thing was the springs should be a tight fit, the rocker arm geometry (we're the rocker arm assem-ba-lee, assem-bah-lee, assem-ba-lee) determines the shape of the collars but seems to me in general they are usually a tad thicker than steel ones, maybe about the same as aluminum. I will direct you to people who can help more than me in a pm.

Is this a better bet that scalloping the steel retainers? Probably 15 - 20% there and easier.
You don't need to do any of this, I'm just one of those people who can't help themselves. Probably a stock rebuild from Engines-R-Us would work fine but some of us is incorrigible ....

btw, you know SCAT in Los Angeles ? They have a ton of experience with VW engines. So if you need something that makes 200 hp then expires in a blinding flash of intense white light (and dollar bills, many dollar bills) then they're your daffodill.

But with all that experience blowing stuff up, they're pretty good at knowing the weaknesses of the engine, too. Pretty nice guys, or they were when we were sending them truckloads of money every week. VW's were very popular in midgets for a while - low center of gravity, light, and you can get a surprising amount of power out of them.

butchah.jpg
 
SCAT is easy to talk to on the phone, but they don't necessarily understand your Q's when it is not coming from a high rpm/high HP screamer perspective.
That's how i ended up with a set of overlength, over force, useless for my app springs. He listened to what i told him, assured me he knew exactly what i needed for (their) C25 cams in my slow revving AC engine, and sent the big ones anyway.

Their single cylinders were a great idea and look like they would be perfect for AC use, but apparently (& they look it) don't have enough finning to shed heat even as well as stock siamesed heads. I keep wanting to like SCAT, though. :) They have products i'll probably eventually use, and it is great there are still a few VW resources. Now that in my dotage i've finally got round to exploring that family of engines after being ignorant of them for 70 years. :)

smt
 
I'd be inclined to find out what people who build VW motors for the Baja 1000 would use. They have to survive under the most extreme conditions.

I bet builder preferences are as varied as the avilibility of different alloys though
 
Unlubricated valves running out in the open on old motorbikes last a lot longer than 250 hours,and my experience with VW engines in buggies ,they never had any excessive valve or guide wear............incidentally ,the old VW repair manuals used to make of point of setting rockers so the valves would be rotated .......a lot of truck engines have positive rotators to keep valve stems straight at operating heat.
 
Unlubricated valves running out in the open on old motorbikes last a lot longer than 250 hours

IME, they last "about" 200 - 300 hrs in hard use, perhaps longer when mostly paraded.
Heck, even enclosed valve Triumphs tended to need a valve job around 15 - 20,000 mi.

and my experience with VW engines in buggies ,they never had any excessive valve or guide wear...........
If they don't have large ratio rockers, i ccould believe that. If they are indeed hot-rod motors, driven like a hot rod, how many actually make 25K miles before top "refreshment". That is a lot of driving on sand.

Keep in mind, an AC engine is used 100% power for maybe 5-10 minutes on take off, then reduced to between 65% to 75% depending how much fuel the pilot enjoys converting to noise, and is left in that position sometimes for a few hours. Not at all a road driving experience where once up to cruise the car is using maybe 20% power to maintain 65=70 mph with occasional squirrely boosts to 75%, when passing, merging, general animal spirits, etc, and motor sees fairly variable rpm over any multiple hour period.

.incidentally ,the old VW repair manuals used to make of point of setting rockers so the valves would be rotated ......
This is still a factor. Setting up with shims to offset slightly so they rotate.

.a lot of truck engines have positive rotators to keep valve stems straight at operating heat.
Aware of that, no personal exposure or experience.

Mostly with the large ratio rockers, the stems go barrel shaped due to constant heavy side thrust. More or less depending on how they are set up (push rod length modded) when first installed.

I'm going to set my rockers up on the surface plate today, and verify the ratio since i neglected to check the overall lift when removing the heads. I have indicated cam lift directly at .330" - .335" both intake and ex. Someone on another site pointed out that intake lift greater than 25% of valve diameter is wasted and merely goes into extra work at the springs and wear in the valve train.


Graph from homebuiltairplanes site
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The intakes on mine are 40mm => optimal lift < 10mm/.394".
I believe currently it has 1.4 ratio rockers which would make lift aprox .465"
If so, plan is to back down to 1.25 ratio rockers which will still have flow benefits of the snappy opening and closing action that over-unity rockers provide.

smt
 
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