My newbie obsessive questions about VW repair

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TFF

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Depends on what you fuel with. Lead is the killer. I remember my dad getting a muffler at Sears about every year as a kid. Almost no car has a muffler rust out today unless in salt county, which I’m not.
 

Aviacs

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TFF -
That is an enlightening observation.
I would rather never use leaded fuel for all the reasons including enviro.
OTOH, landing at other than home-base airports might include 100LL, unfortunately.

However given what you just pointed out, combined with hangar storage, mild steel suddenly looks a lot better than mere "second best".

Thank you!
smt
 

Aviacs

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Early on this advice about parts source was received here, and i stuck to it:

For parts, buy everything from VW Parts - Aircooled VW Parts Catalog at Aircooled.Net and nobody else, exception being aviation specific stuff.

Unfortunately, today the engine shop finally called and said my heads were done.
Upon arrival, the machine work was done, but no assembly - the specs i had emailed a couple times in the past were lost again. So i dug them out of my phone, we commenced to test springs, and they were all low-side acceptable, but one failed. (most 120 - 121 @31 mm, IOW Bob Hoover's specs) low spring was only 112 lbs. Shop had tested seat pressures and felt they were low. (40-ish lbs, IIRC?)

Back at home i went to order a spring set on Aircooled.Net, and they are closed for downsizing and not currently accepting orders.

So, 2 more Q's:

1.) who should i order springs from? It seems the quality is all over the map?

2.)Does anyone know what the seat pressure should be for 35.5 ex and 40mm intakes with a C25 cam?
I suppose on Monday i can call Scat, but maybe there is experience here?

Thanks!
smt
 

karmarepair

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Back at home i went to order a spring set on Aircooled.Net, and they are closed for downsizing and not currently accepting orders.

So, 2 more Q's:

1.) who should i order springs from? It seems the quality is all over the map?
I too noticed this with alarm. Gleaning through old posts, looks like Wolfsburg West for strictly stock stuff (they cater to restorers vice performance/custom trade), CB Performance (John Monnet's original source for engine stuff Back In The Day) or CIP1.
 

curious

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the c25 is pretty mild but, since it's not stock, will have more aggressive ramps. that usually means single HD valve springs and that is what is recommended at AC.net which is one of your preferred providers. what this means is that you will want a seat force, it is force not pressure - look at the units, that is stock or greater. you also want a spring rate that is greater than stock. you get both of those with single HDs. i would guess that a single HD has a stock install seat force of around 120# based on prior interactions i've had at thesamba. your 40# on the seat is way too little.
 

Aviacs

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what this means is that you will want a seat force, it is force not pressure

Technically this is not correct.
What you *want* is a seat pressure: force x area.
This is why i provided the valve sizes. A larger valve might take the same pressure, but it will require more force to attain it.

However, direct absolute force is a proxy for the above, since it is easy to measure directly.

You are semantically correct about the difference between force and pressure.
Clarifying that caused you to become confused about the wants of valve seats.
:)

But i do get where you are coming from.
:)

smt
 

curious

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What you *want* is a seat pressure: force x area.
This is why i provided the valve sizes. A larger valve might take the same pressure, but it will require more force to attain it.
ah, i didn't know you were actually looking for that. the thread says "newbie". spend enough time at thesamba and you will come to know that the mechanics over there (and here too as i'm discovering) use pressure as a synonym for force and don't know that they aren't the same. edited here: i think a good question is why do you want to know/compute seat pressure?

i changed a few things in my valve train (added mass mostly) and was curious as to what the changes in mass were doing to my rpm limit so made a spreadsheet with a load of variables. if you would be interested, i can shove your masses into the spreadsheet and see what happens.

if you don't mind answering. what's your rocker type and ratio? pushrod type? haven't seen either of those in the thread.
 
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Aviacs

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the thread says "newbie"

I'm a complete newbie to VW engines, aircooled or otherwise.
A half century ago, i was a decent motorcycle mechanic including some machining, cc-ing, etc; and also kept a couple of my own Brit sports cars operational. I've wrenched and machined on actual certified, and E/AB airplanes with regular airplane engines. Beyond that i'm a competent manual machinist and design and build tooling and mechanisms to solve other machining problems mostly in wood, but some in metal as well. Hence the obsessiveness, and realization that i don't know anything pertinent to VW's.

I posted rocker ratio in the past but feel it necessary to go back to the hangar and verify my set up.
The quick check, with parts clamped to a piece of plate, yielded 1.4:1. Dial indicator on each side.
The reason i am starting to doubt it is that it seems to be the less common option. And it yields more theoretical lift than i would expect. (Basically, i imagined at the time that if i did a quick check, got a number and then looked online in the catalogs, the closest option would be clear. However, in fact, ratios from 1:1.1, 1:1.25, and 1:1.4 all exist. So more choices than i expected.) I should put a bearing ball in the pushrod end, and an elephant foot on that indicator, to be more confident. Or take it apart and set up on a surface plate to actually measure the part, which i am trying to avoid.

push rods are steel.
Don't know brand, have not weighed, but can at some point.
Your offer is generous and i will try to provide information later.
The past few days and the next few coming are me being back to work on my plexiglass oven.
Need to get that done. I started with an airlift cylinder for the lit, but the lid has gained too much weight and that is no longer safe. Plus an air interruption could be dangerous. So building a motor driven screw to operate it instead.

smt

PS, I know the differences for basic physics units and terminology.
When standing with another guy in his shop checking my springs together who is a life long professional engine builder, i am adaptable enough to understand what he wants when he asks me to find "pressure" and think nothing of it. Swapping between metric and english terms and units adds to the options for sloppiness. Perhaps posting with sloppy terminology is a bit lax on my part, though. Thanks for the note!
 
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Wiseacre Dave

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Technically this is not correct.
What you *want* is a seat pressure: force x area.
This is why i provided the valve sizes. A larger valve might take the same pressure, but it will require more force to attain it.

However, direct absolute force is a proxy for the above, since it is easy to measure directly.

You are semantically correct about the difference between force and pressure.
Clarifying that caused you to become confused about the wants of valve seats.
:)

But i do get where you are coming from.
:)

smt
Pressure is force per unit area, P = F/A, not F x A.
 

TFF

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The springs need to match the cam. If you have a Scat cam, they have correct springs. Sounds like some stock springs you bought meant for stock cam.

Mostly we are just readjusting spring rate numbers. 1” rate is X. Then we extrapolate what it should be open and closed and hope the manufactured part matches.

The springs keep the lifter on the cam and keeps the valve from going random places. You know that. You don’t need more and you don’t need less.
 

Aviacs

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The springs need to match the cam. If you have a Scat cam, they have correct springs.

One hopes.
I was double checking advice from here to stick with a specific different supplier as being most reliable.
Scat does not have good current reviews for promptness/customer relations, and i spent a good part of a day last week trying to get through to them before meeting with my engine guy.

Sounds like some stock springs you bought meant for stock cam.

I have not bought springs.

Per the analysis, though, who knows? They are original to the GP original build, but not that old in terms of hours.
BTW, Stock VW springs have among the best rep, but i have not checked if they have the appropriate rate.
Been stacking firewood - Thanks for the reminder to call "some supplier" before the day is over.

smt
 

karmarepair

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RE Spring Rate - we are trying to prevent valve "float", where the lifter loses contact with the cam. Aggressive, high lift cams make this more likely, but so does RPM. Most VW aftermarket cams, and their accompanying springs, are aimed at HIGH RPM. A direct drive VW aeroengine is probably NEVER seeing more than 4000 RPM, with 3200 - 3600 more likely on anything but a Formula Vee racer. Well matched stock springs or at most, single HD springs, are ENOUGH, and will cut down valve train wear vice the radical jockstrap springs drag racers need for 8000 RPM launches.
 

Aviacs

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RE Spring Rate - we are trying to prevent valve "float", where the lifter loses contact with the cam. Aggressive, high lift cams make this more likely, but so does RPM. Most VW aftermarket cams, and their accompanying springs, are aimed at HIGH RPM. A direct drive VW aeroengine is probably NEVER seeing more than 4000 RPM, with 3200 - 3600 more likely on anything but a Formula Vee racer. Well matched stock springs or at most, single HD springs, are ENOUGH, and will cut down valve train wear vice the radical jockstrap springs drag racers need for 8000 RPM launches.

The springs keep the lifter on the cam and keeps the valve from going random places. You know that. You don’t need more and you don’t need less.

Preaching to the choir.
This is why it is important to check the seat force (or pressure) and the force at heights specified by "an entity that knows".
Otherwise it's all guesswork.

To wit - the people who are resisting my attempts to "express (understand) it in numbers" ("when you cannot express it in numbers your knowlege is of a meagre and unsatisfactory kind") - per Lord Kelvin, which longer version my dad was fond of quoting - would have missed the weak spring in the batch. Or even the fact that all the springs are a little toward the light end of spec. You can bet i'll test the ones that arrive, assuming they do, before installation.

To answer your implied question, checking each spring can show if the springs are too "light" or too "heavy" for the app If someone knows what the standards actually are. At least until they run a while, then the purchaser is at the mercy of the manufacturer's integrity for design and process control, AFA durability. So people ask on forums to see what the inside dope is: whose product is holds up over time, and whose might not.

smt
 
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TFF

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You need to buy a Bentley manual or VW USA one. No one so far is giving it up for free. There are only four or five spring options on the market. You don’t have infinite choices. You don’t like the stock springs, and you don’t need some that rev to 8000, it only leaves one or two options left.
 

Pops

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Why all the worry about valve float at 3600 rpm or less on a VW driving a prop ? A good set of stock valve springs is good. I have more important things to worry about. Heat? Running the engine to hot can cause many different problems.
 

Aviacs

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I'd drop this and move on, as i think "through experience of several wrong orders/mistakes" i have solved this for myself. However, as an archive for someone in my situation in the future i'll keep posting the journey. Par for the course on many forums, so far, all of the answers re: springs are about what the poster wants to talk about, not the info requested.
Actual Q's

1.) who should i order springs from? It seems the quality is all over the map?

2.)Does anyone know what the seat pressure should be for 35.5 ex and 40mm intakes with a C25 cam?
I suppose on Monday i can call Scat, but maybe there is experience here?

Apparently Scat's single springs (ordered/drop ship by me/received by my engine builder/head guy on Friday) are for use with high lift/high rev engines. Engine builder feels that at 120 lbs installed seat force, they are much too heavy, and they are longer than stock, which suggests to him that the typical install might include machining the heads spring seat pockets to avoid coil bind.

He's headed to FLA for the winter on Monday.
At least the machine work is done, and i will complete the set up in my own machine shop.
Going to try ordering yet another batch of springs from Wolf, and will build a simple spring force tester from a scale and a stray auction box-lot mechanical press.

Ski season started all around me except the 2 hills my season pass is good for :(
However, as soon as they catch up, this will be on the back burner, hoping for a very long, cold winter with lots of snow. :) Re-starting work on the canopy oven, in the nonce.

smt
 
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