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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #30 on: July 04, 2016, 01:05:29 PM »
I wonder what the normal operating temperature on top side of engine block? I noticed today that a little water that splashed in was boiling for 3-5 minutes after stopping. Is that how it supposed to be (outside temperature is 70F,  by the way)? Maybe I should take a picture with Seek Thermal next time I am out and water is flat. The enlarged plenum Tom developed with something on top to protect from splashing water sounds better and better :)

Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #31 on: July 04, 2016, 02:29:55 PM »
The oil temps can reach 300f in a stock motor with stock plenum and standard oil. So seeing water boil on the block wouldn't be anything unusual on any of these motors, even one that is running at cooler temps. My oil temps will be 250f after 5 miles. Welcome to air cooled engine fun. hehe
 ;)
Tom

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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #32 on: July 06, 2016, 11:38:15 AM »
Tom, what do you think of expanding plenum by heating it up with torch and exerting pressure from the inside with suitable pieces of wood? It seems to me that 20-30% expansion in cross-section area can be easily achieved, maybe more. Combined with cutting off the choking neck on top that should substantially improve engine cooling, right?

Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #33 on: July 06, 2016, 02:59:51 PM »
I doubt that would work without deforming the mating surface to the engine. Best to cut and graft in a spacer to enlarge.
Tom

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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #34 on: July 06, 2016, 03:55:31 PM »
I doubt that would work without deforming the mating surface to the engine. Best to cut and graft in a spacer to enlarge.

Tom, you are absolutely amazing!!! I started doing what I described before reading your prediction and sure enough discovered for myself that the bottom circular surface has indeed distorted. Also, the carb outlet started to get away from the carb. Fortunately I stopped early enough to see the alarming trend. To reverse the unwanted effects I've mounted plenum on engine, put ties to strain the areas coming out of alignment and started heating again (with emptied carb  :). After letting it cool plenum mounts and dismounts fine, making good contact at the bottom and at the carb. But the overall enlargment was certainly less than 20-30% I anticipated.  Still, with a narrow neck cut off and a little widening I think I am ahead except for one thing: Stock plenum makes pretty tight contact with black rubber band in the cover. I had to remove rubber band on account of enlargement and so there are few gaps now. Aside from water coming in through those gaps, do I need to worry about wrong airflow? Like warm air expelling from those gaps being sucked in back into the engine? What do you think?


Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #35 on: July 06, 2016, 04:00:09 PM »
Glad you stopped before it was too late.  :-O

When I enlarged mine, I cut the hood opening so it could come through. There is a small gap all the way around the plenum and that doesn't cause any problems so don't worry about having removed the rubber trim on yours. Removing the pull starter also helps the airflow, but if you do that you'll want some type of grate over the plenum so nothing can go down into the flywheel.
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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #36 on: July 07, 2016, 09:52:59 AM »
I see, thanks for explaining.

On a related subject, when do you think temperature in engine compartment and/or engine temperature itself is highest? While running continuously at idle (3 mph in my case), or half top speed - 6 mph or somewhere in between? What makes it difficult to understand is that both heating and cooling change at the same time. My rough measurements with infrared thermometer (extend hand back and point thermometer down one of the engine vents) produced almost unchanging 160-170F while running at different speeds and definitely raising after stopping the engine. Maybe I should attach a thermocouple to some point on engine block to get more accurate reading...

Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #37 on: July 07, 2016, 10:06:35 AM »
Temps will be highest after sustained 4-5 miles of full throttle operation. Engine compartment temps would be in the range you noted, and the reason I went water cooled with the muffler and enlarged the plenum. Temps are now less than 120f in there, oil temps are 40-50 cooler too. With no airflow after shutdown, it will get hotter for a while which can contribute to hot start issues.
Tom

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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #38 on: July 07, 2016, 11:03:17 AM »
If one wants to cool the engine off before shutdown should one go to idle or to a low/medium throttle? What would you choose?

Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #39 on: July 07, 2016, 11:08:01 AM »
Idle would cool down fastest, no  load (or reduced, without clutch) on engine. 5 minutes of idling helps a lot.
Tom

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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #40 on: July 07, 2016, 12:34:00 PM »
Got it. Thanks a lot!

Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #41 on: December 10, 2016, 03:58:31 PM »
. Oh, I also do not have the recoil starter on. With electric start there is no reason to have that there interfering with air flow, the more the better.  \./8

Do you recommend to remove the recoil starter combined with the grate (the thing bearing Subaru logo) or detach the starter from grate and leave the grate?

And one more question. I recall someone mentioning that the air plenum won't fit if the recoil starter is removed and so some minor modification is required. I searched the forum but just can't find that post. Is my memory faulty? I tried to remove the starter myself and found that plenum fits just fine...

Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #42 on: December 10, 2016, 04:29:25 PM »
You can take the whole recoil assembly off, there is no need for any of it if you have electric start as long as you trust it. lol Has nothing to do with the air plenum fitment. The bolts holding the recoil assembly might need to be swapped for some shorter ones if they hit the flywheel fan, they hold the plenum's fixing ring to the flywheel cover.
Tom

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Offline happul3

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Re: Air Shroud and Engine Cooling
« Reply #43 on: December 10, 2016, 05:32:04 PM »
Thanks Tom! After removing the assembly inclusive of the grate, should I fashion some some sort of mesh at the top of air plenum to protect the fan?

Offline Painlesstom

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Re: Air Shroud and Engine Cooling
« Reply #44 on: December 10, 2016, 07:12:46 PM »
If you play in places where you could run under brush and end up getting leaves or sticks sucked in the intake scoop, some type of mesh would be appropriate. Open water there would be no need.
Tom

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