Lawnmower cowling on the 4 stroke motors

GearNut said:
Motorcycle engines also have longer cooling fins to allow that.
A forced air cooling system generally has shorter fins to make the whole assembly more compact.
They are matched to the task required.
Click to expand...

I just want to second that opinion. I have an old air cooled VW and one the important things to ensure no overheating is that the shrouds are all in place a decent engine is designed the way it is for a reason.

But some stuff is over engineered or engineered for worse case scenario. Like the old Russian MZ motorcycles, they were a dime a dozen in Nicaragua with a spotty performance record due to an air cooled engine engineered for the Russian climate being run in a tropical country.
 
Yep, those shrouds are critical on the old VWs! I found that out the hard way years ago!

Anyway, it's amazing what people will do in the name of aesthetics to something that works well as designed.
If anything, the shroud's best purpose is that it keeps the engine at a near constant temperature once it's warmed up.
It could definitely look better, but I painted mine black from the get-go and have no problems with how it looks. It does it's job.
 
Well this is a bummer then. LOL

Ran the HF 79cc in 100F at idle for 15 mins with and with out the heat shroud. It ran 7 degrees cooler with.

Underway, ran cooler with it off. Test ride one way with, was about 7 mins and 7 back with out.

I used an inferred thermometer and am gonna retest using a wired gauge. It was hard to read as the numbers jumped greatly. But am not putting the shroud back on other then for testing until next winter.


.wee.
 
Last edited:
Sitting here looking at the HF and Predator engines, while it really does look a whole lot better with out the shroud and helps cut down on the lawn mower look, my wanting to remove the shroud is more that I want them to run as cool as possible this time of year and it just dawned on me, more with a lower profile engine then the Honda/clone (Clonda? snork), it also shields the head from the muffler. As it is not there any more, lessons the need for the shroud.

Dunno, am I wrong there?


Now I really gotta do a powder coat job on the right side covers. That makes a world of difference with their looks. (Can't stand the HF blue. The predator is much better looking black and does not scream "lawnmower, me thinks)
 
Dan said:
Sitting here looking at the HF and Predator engines, while it really does look a whole lot better with out the shroud and helps cut down on the lawn mower look, my wanting to remove the shroud is more that I want them to run as cool as possible this time of year and it just dawned on me, more with a lower profile engine then the Honda/clone (Clonda? snork), it also shields the head from the muffler...
Click to expand...

Back to the VW egineering, there is a cheap foam seal/gasket that seperates the top half of the engine from the bottom. It is usually missing as it will deteriorate with time but it is the biggest contributor blown engines as most guys ignore it , but it actually keeps the heated exhuast air from getting sucked into the shroud. Air cooling an engine with super heated air is kinda counter productive.
 
I've been running Briggs motors without shrouds for around 25 years with no overheating issues. Their fins are really overkill because the manufacturer knows the user will never clean the grass from them. I also like to re-design the shroud to make it fit nicer and protect my leg from the flywheel.




DSCN0303.jpg


DSCN0239.jpg


SDC10864.jpg


DSC00828.jpg

DSC00825.jpg
 
MSRFAN, how did you thread the shaft to get a retaining nut on? Also is it left hand thread? Working on a thing and want to cut off both sides of the shaft a bit and am not sure how to secure sheaves on both sides.

As always, great builds!
 
Thanks Dan. The shafts on Briggs motors are already threaded for a nut to retain the flywheel. There's no easy way to fasten a pulley to the right side. Some machine work will be needed. If I wanted to put a pulley on the flywheel side, I would have the a pulley bored to 1'' and then have a stepped nut made to slip through the pulley onto the shaft holding the pulley centered when torqued in place. Also a roll pin tight in the flywheel and a slip fit through the pulley would ensure it didn't unscrew the nut, and would allow easy removal. There's lots of different ways to accomplish the same thing. This is just the way I would do it. Maybe someone else will have a better way. Hope that helps. Let me know if you need a drawing or more info.




Dan said:
MSRFAN, how did you thread the shaft to get a retaining nut on? Also is it left hand thread? Working on a thing and want to cut off both sides of the shaft a bit and am not sure how to secure sheaves on both sides.

As always, great builds!
Click to expand...
 
Thanks Mon!

I am thinking a sort of ear-muff thing. With a bearing to hold in the sheaves. The belt will help and am thinking this more a fail safe. Another "try it and see"

Don't mean to ramble so far off topic and will start a thread before this build.


Still running with out the heat shield. No problems so far.
 
Dan said:
Well this is a bummer then. LOL

Ran the HF 79cc in 100F at idle for 15 mins with and with out the heat shroud. It ran 7 degrees cooler with.

Underway, ran cooler with it off. Test ride one way with, was about 7 mins and 7 back with out.

I used an inferred thermometer and am gonna retest using a wired gauge. It was hard to read as the numbers jumped greatly. But am not putting the shroud back on other then for testing until next winter.


.wee.
Click to expand...

Thanks for this info Dan. but i think the significence needs to emphasised.

For all that beleive the cowling is needed, Dan's results show that for Honda's intended usage, your absolutely right. That is, 15mins at idle & stationary it will run hotter. 15mins is a VERY long time to sit there idling, 3mins for that matter is quite a long time. So running your engine for extended periods while stationary will run hotter without the cowl.

But for the rest of us who use this engine outside of honda's intended purpose, ie mount it in a bicycle & go ripping down the street. Dan's results show a reduction in temperatures under the conditions that are most relivent to us; under load & at speed, not idling stationary on hot ground like a generator motor might. Given that you will also be coming to an idling stop ,from a lower operating temp(from riding around), increased idle temp is not likely to be an issue, and it wont jump instantly.

If you want to use this motor as intended by honda, best place it on the ground, connect a water pump & walk away.

For riding around r.ly. i think you would be well served to remove them.

Just my interpritation on Dan's hard work. I will certainly be pulling the cowls of my Honda when she arives.
 
I just removed mine - the trick is, you have to get 3 spacers or the pull start will rattle around like crazy. Other than that (which was an excuse to ride to the hardware store), it's a 2 minute job. Looks a lot less like a lawnmower engine strapped to a bike now.
 
After a few rides - one wearing shorts - I can say that without the cowling, there is definitely a warm breeze on my leg when I stop...
 
well, a warm breeze sounds managable at worst & pleasent in cool conditions. is it radient heat you now feel that was otherwise blown off in some other direction when the cowl was on? Or do you think it is getting really hot really quick at idle?
 
it's just the flywheel blowing hot air right up my pant leg. A non-issue when moving and curiosity when still...
 
Next ....Has anyone removed the pull starter with a SBP shift kit and just pedal started the thing by popping the clutch. It would seem so easy to clean up the whole right side of these motors. Pedaling at 6-7 mph and having a that momentum should do the trick.
 
Welcome to the forum, Max Power. The clutches on the 4-strokes are centrifugal, not manual.

Therefore, it's not possible to pedal-start it. There is no provision for a manual clutch available.
Additionally, most gearboxes have a freewheel in their system. Removing or disabling the freewheel negatively impacts the ability to pedal with engine off.
 
Ok ....But all of the kits I have been looking at say the come with "Push button clutch lever (for easy pedal clutch lock out)" with instructions that say to pedal up to 5mph before releasing the clutch lever. I have done a lot of Cent clutch motorsports and have never seen a lock out for a Cent clutch.
 
You must log in or register to reply here.
Back
Top