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40 HP Stale Engine Thermostat Adjustment
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Exnermobiles
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PostPosted: Tue Jan 24, 2023 2:30 pm    Post subject: 40 HP Stale Engine Thermostat Adjustment Reply with quote

Hello everyone!

I’m assembling my 40 hp stale engine and trying to understand the thermostat adjustment procedure described in the Bentley manual. I have followed step by step the procedure “Adjustment when Assembling Engine”:

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When I complete step 4. the throttle ring becomes pre-loaded because the thermostat itself is pre-loaded in its bracket. Now the thermostat is not at all in its fully retracted state even when the engine is cold:

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However, when heating the thermostat with a heat gun and when the thermostat becomes fully extended (touches the top of its bracket) the gap between the fan shroud and throttle ring is well within the given limits:

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According to Bentley the gap should be between 25 and 30 mm:

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Everything seems to be alright but I’m still wondering if the thermostat is supposed to be pre-loaded like that. When combining the pre-loads of the throttle ring spring and the thermostat I would not say that the throttle ring is “slightly pre-loaded” against the shroud. I think it is now more like “moderately pre-loaded”.

Can someone tell if this is normal or if something has gone wrong with my thermostat adjustment?

The thermostat is a NOS VW part:

Image may have been reduced in size. Click image to view fullscreen.

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pastellgreen
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PostPosted: Tue Jan 24, 2023 3:01 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

you made it right. The preload is not weak.
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PostPosted: Tue Jan 24, 2023 8:45 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

It has to be too much preload. Is the mechanism getting hung up on something?
It will eventually get as big as the thermostat bracket regardless of preload.
Edit: I thought your thermostat was being stretched open by preload but I think I misunderstood.
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Last edited by DeathRay64 on Thu Feb 02, 2023 6:18 pm; edited 1 time in total
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steven wardlaw
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PostPosted: Wed Jan 25, 2023 9:35 am    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

Just make sure that when the engine is fully warmed that you have about an inch of clearance from the ring to the shroud. If it's over that you will hear the ring grinding away against the fan blades. I drive mine and check it hot. It doesn't take long after you shut down the engine for the bellows to start closing up the gap.
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PostPosted: Wed Jan 25, 2023 9:55 am    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

steven wardlaw wrote:
Just make sure that when the engine is fully warmed that you have about an inch of clearance from the ring to the shroud. If it's over that you will hear the ring grinding away against the fan blades. I drive mine and check it hot. It doesn't take long after you shut down the engine for the bellows to start closing up the gap.


Wait, you're saying that the ring will rub against the fan blades after it has pulled away from the fan?
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pastellgreen
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PostPosted: Wed Jan 25, 2023 12:31 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

scottyrocks wrote:
steven wardlaw wrote:
Just make sure that when the engine is fully warmed that you have about an inch of clearance from the ring to the shroud. If it's over that you will hear the ring grinding away against the fan blades. I drive mine and check it hot. It doesn't take long after you shut down the engine for the bellows to start closing up the gap.


Wait, you're saying that the ring will rub against the fan blades after it has pulled away from the fan?


This is correct!
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PostPosted: Wed Jan 25, 2023 12:40 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

How tall is the rubber bumper on the throttle ring, measured from the ring to its face which contacts the fan housing?
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PostPosted: Wed Jan 25, 2023 6:35 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

pastellgreen wrote:
scottyrocks wrote:
steven wardlaw wrote:
Just make sure that when the engine is fully warmed that you have about an inch of clearance from the ring to the shroud. If it's over that you will hear the ring grinding away against the fan blades. I drive mine and check it hot. It doesn't take long after you shut down the engine for the bellows to start closing up the gap.


Wait, you're saying that the ring will rub against the fan blades after it has pulled away from the fan?


This is correct!


I agree.
The ring rubs if it opens up too much.

This is something to check or ask if you are buying a used ring.
A lot of them have wear from rubbing in the past.
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PostPosted: Thu Jan 26, 2023 12:06 am    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

pastellgreen wrote:
scottyrocks wrote:
steven wardlaw wrote:
Just make sure that when the engine is fully warmed that you have about an inch of clearance from the ring to the shroud. If it's over that you will hear the ring grinding away against the fan blades. I drive mine and check it hot. It doesn't take long after you shut down the engine for the bellows to start closing up the gap.


Wait, you're saying that the ring will rub against the fan blades after it has pulled away from the fan?


This is correct!


How is this possible?
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pastellgreen
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PostPosted: Thu Jan 26, 2023 5:20 am    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

scottyrocks wrote:
pastellgreen wrote:
scottyrocks wrote:
steven wardlaw wrote:
Just make sure that when the engine is fully warmed that you have about an inch of clearance from the ring to the shroud. If it's over that you will hear the ring grinding away against the fan blades. I drive mine and check it hot. It doesn't take long after you shut down the engine for the bellows to start closing up the gap.


Wait, you're saying that the ring will rub against the fan blades after it has pulled away from the fan?


This is correct!


How is this possible?


I'm not a native speaker, for me too hard to explain.
Start your engine, grab the throttle ring and pull it out more than the thermostate would do. You'll see the result.
When you look at a sketch with a cut through the fan house, you see why this is possible:

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The inner edge of the throttle ring touches the fan when too much opened.
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PostPosted: Thu Jan 26, 2023 10:44 am    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

Thank you for the visual.

I am actually still in the process of deciding on whether or not to do the thermostat system install myself, as I finally have all the correct parts.

I have seen the diagram that shows the adjustment for the throttle ring to be 20mm when fully in the out position. I had presumed that number was arrived at as a combination of the starting closed position, and the limited movement of the t-stat, itself, and the rest of the Rube Goldberg system that eventually moves the throttle ring. Stat expands, pushes up rod which pushes up and rotates rotates arm which rotates main shaft which moves ring out. Total distance = 20mm.

Basically, if the ring is more than 20mm out at max, it won't be closed all the way when the engine and t-stat are cold, yes?

Is this a 'safety' feature, as in - if you hear your fan hitting the ring, it's not closing all the way when the engine is cold so adjust it?
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PostPosted: Thu Jan 26, 2023 12:08 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

scottyrocks wrote:
Thank you for the visual.

I am actually still in the process of deciding on whether or not to do the thermostat system install myself, as I finally have all the correct parts.

I have seen the diagram that shows the adjustment for the throttle ring to be 20mm when fully in the out position. I had presumed that number was arrived at as a combination of the starting closed position, and the limited movement of the t-stat, itself, and the rest of the Rube Goldberg system that eventually moves the throttle ring. Stat expands, pushes up rod which pushes up and rotates rotates arm which rotates main shaft which moves ring out. Total distance = 20mm.

Basically, if the ring is more than 20mm out at max, it won't be closed all the way when the engine and t-stat are cold, yes?

Is this a 'safety' feature, as in - if you hear your fan hitting the ring, it's not closing all the way when the engine is cold so adjust it?


Without the spring in action, the thermostat loosened, you adjust to 20mm. After tightening the thermostat and reinstall the spring, during a test with a heat gun the throttle ring should be open between 25 - 30mm. The spring causes a wider opening than the 20mm. The spring is strong and designed to 1. push the ring open in case the thermostat fails and 2. to avoid any play (and rattling) in the mechanism. It is the preload of the thermostat only that assures the throttle ring to be closed with preload against the fan housing (and this against the pressure of the spring) when the engine is cold.

Therefore: in my opnion, the op had done a good work and should leave the already correct working system as it is.
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scottyrocks
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PostPosted: Thu Jan 26, 2023 1:42 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

Okay, so the initial adjustment is 20mm. Thanks!
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PostPosted: Thu Jan 26, 2023 8:32 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

pastellgreen wrote:

Without the spring in action, the thermostat loosened, you adjust to 20mm. After tightening the thermostat and reinstall the spring, during a test with a heat gun the throttle ring should be open between 25 - 30mm. The spring causes a wider opening than the 20mm. The spring is strong and designed to 1. push the ring open in case the thermostat fails and 2. to avoid any play (and rattling) in the mechanism. It is the preload of the thermostat only that assures the throttle ring to be closed with preload against the fan housing (and this against the pressure of the spring) when the engine is cold.

Therefore: in my opnion, the op had done a good work and should leave the already correct working system as it is.


Thank you pastellgreen - this makes very much sense! I feel now more confident with the adjustment I have done.

The fact that the thermostat is constantly preloaded when the engine is cold is not highlighted anywhere in the service manual.
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PostPosted: Thu Jan 26, 2023 8:54 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

mukluk wrote:
How tall is the rubber bumper on the throttle ring, measured from the ring to its face which contacts the fan housing?


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


I hope this clarifies.
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PostPosted: Fri Mar 01, 2024 9:32 pm    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

thank you for your post, nice with pics.
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Nitramrebrab72
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PostPosted: Sat Mar 02, 2024 12:54 am    Post subject: Re: 40 HP Stale Engine Thermostat Adjustment Reply with quote

Beware if you have too much tension on the cable when cold you will prematurely split the diaphragm. Did you check the difference in height if any of the diaphragm in the freezer.???
Better slightly less tension than too much.
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