New Tecumseh 11hp engine... Question on RPM... - Snowblower Forum : Snow Blower Forums
 
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post #1 of 9 Old 03-22-2016, 10:26 PM Thread Starter
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New Tecumseh 11hp engine... Question on RPM...

Hey guys, I just got the 1999 Craftsman 28" EZ-Steer snowblower completely rebuilt and put back together.

I put on a new LH358XA 11hp engine (10hp long block with a new 35980A crankshaft and PTO 2:1 camshaft with the higher compression headgasket to get 11hp) along with a 3amp DC stator (actually puts out more like 6-7amp @ 14.8v). I also put on an adjustable carb and tuned it properly for idle and high-rpms.

At idle it idles around 1950-2000 rpms. The question I have is in regards to what the max rpms I should be shooting for?

Now, the 10hp long block was rated at 3750rpm +/- 150 rpm. This was for generator duty.

Most of the info I have found online all say the l-head engines are expected to run 3600rpm +/- 100 rpm as the operating RPM. But this is not from manufacturers or anything on a spec sheet, just hear-say from people.

Actually, most say that most snowblowers are set to run at 3150-3300 rpm from the factory, with Ariens and some other maker stating they run at 3600-3650 or so. Toro was spec'd at 3300-3500 rpm I believe for thier older models that ran Tecumseh l-heads.

I just want to know what RPM I should shoot for here. I started out with it at 3300 rpm. I found that out when I hooked up the tach and checked it. I bumped it up to 3800rpm and it made a noticeable difference in the impeller/auger speed and the amount of air being shot out of the chute.

I just find it strange that they would rate a motor at 3750 +/- 150 rpm and then everyone it running them at 3600 (which is the low-end of that spec, but why not run it at the middle of spec, if not even the high-end of spec at 3900rpm???)

I run Mobil1 high mileage 10w30 full synthetic oil in it (I prefer the better anti-wear additive package the high-mileage version includes). It is kept in a heated garage.
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post #2 of 9 Old 03-22-2016, 10:53 PM
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If it was on a generator it was run at whatever RPM was needed to provide 60 hertz. 3750RPM seems a little high to me, but with a constant load it should stay together.

3600RPM has always been the standard operating speed for small engines and the RPM used to rate horsepower. Some of the later Tecumseh OHV engines were tuned to run at 3400RPM but otherwise 3600RPM is what you should be shooting for.
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post #3 of 9 Old 03-22-2016, 11:28 PM Thread Starter
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Yeah, this was a brand-new generator engine, never even fired when I got it. I stripped all the non-snowblower stuff and mounted all new snowblower parts to it to make it a snow king engine. The crankshaft is new as is the camshaft.

I just want maximum performance out of this engine. The original engine on the stock snowblower was a 9hp unit that had a non-adjustable carb and it had a long useful life, since the original issue I had was a stretched exhaust valve and reduced power and high exhaust temps.

The rebuild was a complete tear-down, replaced every cable/belt/spring/bushing/bearing/washer/worn part with new, engineered a better driveshaft (modified with roller bearings inside and outside), new auger housing, sandblasting of all to be reused parts and both powdercoating and painting to seal and color-match all parts. It used to be Craftsman Polo Green and it is now Troy-Bilt red with black bracketry/augers/impellers/handlebars. I used the 42" bucket reinforcement bracketry to reinforce the auger gearbox and added in an OEM electric chute control for horizontal chute articulation.

Basically, it is a new snowblower, in every way-shape and form. The only thing "old" is the control panel and that is in excellent shape.
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post #4 of 9 Old 03-23-2016, 05:46 AM
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You'll have to post some pictures of your work.
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post #5 of 9 Old 03-23-2016, 08:43 AM
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wow - you really went over the top there Dennis! I only wish I had a heated garage! I need to look at doing something about that this summer - on top of 1000 other projects awaiting me! Good news is You might get one last chance to try out that blower on Thursday! It's going to miss me by about 6 counties to the north.......




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post #6 of 9 Old 03-23-2016, 11:41 AM
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I'd focus on keeping the engine RPM low -- so ~3600 -- and if you want more impeller speed use different pulleys to attain the ratio you want. Leverage the torque of that motor and operate it conservatively.

Also look into an impeller mod and keeping the ratio as is. Making the pump more efficient has a huge positive effect on the effectiveness of the blower without over-speeding anything.
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post #7 of 9 Old 03-23-2016, 12:53 PM
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Quote:
Originally Posted by 94EG8 View Post
If it was on a generator it was run at whatever RPM was needed to provide 60 hertz. 3750RPM seems a little high to me, but with a constant load it should stay together.

3600RPM has always been the standard operating speed for small engines and the RPM used to rate horsepower. Some of the later Tecumseh OHV engines were tuned to run at 3400RPM but otherwise 3600RPM is what you should be shooting for.
My Generac generator states in the service manual to adjust it to (I'm going by memory) 61-63 Hz (3660-3780 RPM), with no load. The mechanical governor isn't perfect. So under a load, the RPM sags somewhat, closer to the proper 60 Hz (3600 RPM).

Given that, a suggested speed of 3750 doesn't strike me as terribly weird for a generator engine. If it's what suggested for the engine, I wouldn't feel terrible about running it at that speed. And if you want to normally run it a bit slower, and crank the throttle to the higher speed when needed (maybe you need more throwing distance), that would certainly be an option too.

Ariens 1024 Pro
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Toro Power Curve 1800
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post #8 of 9 Old 03-23-2016, 01:26 PM Thread Starter
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Yeah, I originally was going to do an impeller mod to it, I even bought the kit on ebay for it, but after I bought it and before I rebuilt this blower I ended up getting a 24" newer model Cub Cadet and ran that and was impressed on the blowing ability with a motor running at proper RPMs with decent power. So I figure I will run this one without the kit and if I need to add it later I will.

I figure the bump in HP and engine speed might just give it an edge to perform the way I expect it to.

For us with the lake effect of lake Michigan we are only planning on getting rain/sleet and maybe some light snow... No major snowfall predicted for us. But, then again, I almost guranteed that by getting the snowblower rebuilds finished in the past few weeks, right?

I will take a bunch of pics of this blower along with the 21" 2-cycle rebuild I did at the same time and post them in a new thread. That one has a HSK850, so I bumped the RPMs to increase the HP from 4.75hp to about 5.5hp. Internally it was in perfect condition and I had to reseal the engine crankcase, so I also cleaned out the muffler and added in a brand new starter (when I got the blower the starter was missing), added in a new ignition coil, rebuilt the carb completely, then proceeded to replace the auger with a new style one, new belt, new pulley, sandblasted and powercoated the housing, new scrapper bar, all new stainless hardware, new chute and set it up properly on rebuild.

Last edited by DennisP; 03-23-2016 at 04:31 PM.
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post #9 of 9 Old 03-23-2016, 04:19 PM
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I just got a Murray 21" with exact same setup...... starter was bad. Didn't really want it but neither did anybody else..... got it for a Dollar. Spent about $5 on hardware and it runs like a champ. Just going to sell it..... have way to many as it is. I'm going to tey draggin some to the swap meet in a few weeks to unload them. Gotta make room for the mowers.....




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