That's an interesting possibility too. I guess if the Sears has a relief valve and it's way out of adjustment, it would make it harder to spin. In retrospect, I wish I had taken out the spark plug and seen how it would spin that way. And I also with I had thought of Hank's advice of checking that the engine can spin freely and isn't being held back by a belt, etc.
You guys expect me to believe that the exhaust valve timing varies based on engine rpm? I'm having a little trouble with that since I'm thinking that pretty much all these small engines have a purely mechanical valve train. Is compression lower during cranking because of valve overlap? Sure I'll agree with that. That's true on any engine with a mechanical valve train and some overlap in the valve timing. Not a lot of difference though. Even with racing cams cranking compression is still 2/3 to 3/4 of running compression. And because of the low rpm that is the normal operating band of these engines any valve overlap is going to be a lot less than a racing cam.
And out of adjustment causing enough of a difference in compression to stop a starter, that's a bit harder to swallow. It would have to be so far out of adjustment that it would be pretty noisy during running.
Why would you even design a starting system that couldn't crank a 4 stroke engine this small without some sort of compression relief? It's not like it's difficult to find a starter that would do it. The starter on my 1100 cc 4 cylinder motorcycle is small enough to hold in your hand. My motorcycle has no compression relief. And it's battery is smaller than the battery on my neighbors deere lawn tractor.
The sears guy might have adjusted the valves but that had nothing to do with the problem. My money is still on connection issues that just "improved" after the sears guy messed with it.
Don't know whether we expect YOU to believe us or not, but there IS a "governor-like" component on MANY cams in small engines that changes the exhaust valve timing/opening depending on speed.
Go to
So now you don't need to believe US any more.
As for your 1100cc bike - it is a FOUR cylender engine, so there are not the (cranking) torque peaks involved that there are on a single.
I don't know what they have on lawn tractor size engines and in general I agree with you. However I have a craftsman self-propelled mower and one of the things that feature is that it has some type of compression release that eases pull starting. I don't know how it's implemented, but assume it somehow reduces compression until the mower gets going.
That was my thoughts too.
Agree with all that too. Which is why when it wouldn't spin the engine with a car battery connected directly to the starter, I told the neighbor to buy the new starter.
Except of course that it performed the same way with the lawn tractor batter and starter solenoid system and with both the lawn tractor battery and my fully charged car batter directly connected to it via jumper cables. The ground path was to a large clean metal bolt directly on the engine and the starter has bolts that bolt it down to the engine. In addition it;s tightend against the engine.
The only logical thing I'm left with is that per Hustlin Hanks' suggestion, maybe something was binding the belt connected to the engine so it took more force to turn it. But one would think if that was the case it would be likely that with the mower running, some belt would start burning or smoking.
Since it wasn't my mower, I didn't have an opportunity to perform any other testing. The only interesting thing is the neighbor did say while it mostly starts ok now, it has hesitated at least occasionally. So, I'm guessing something is still going on.
Maybe you can search for info on a Wisconsin model TRA-12D engine and educate yourself. You are partially correct though, it is a completely mechanical design.
Ok, I'm going to assume that yes there are some esoteric engines out there that had some such thing to relieve compression. I'm not disputing that such things exist. I know that it was much more common on diesels. Did your wisconsin tra-12d engine have an electric starter? Just what was the last year that your tra-12d engine was manufactured? Cause I've seen a whole lot of internal combustion engines in the last 30 years and I have never run into one that had compresion relief other than a handful of diesels.
I'm doubting that this even remotely has anything to do with this 7 year old sears riding lawn mower starter problems.
I'm doubting you are making any attempt at educating yourself about something that is fairly common. I won't waste any more time with you since you are too lazy to research this yourself.
Not just too lazy, buttoo stupid to take information handed to him. MOST recent small 4 stroke engines have automatic compression release. It is NOT esoteric, in the least.
I asked a bunch of questions about your tra-12d engine. I got no answers. It sure doesn't generate many google hits. About the only one that looked marginally useful wanted me to buy the service manual. A lot of the results seemed to be about antique tractors. I do know that as the displacement goes up if you were going to hand crank it then compression release was more common in the way back when. Today most everything you buy that has significant displacement has a battery and a starter. The population at large is not really interested in hand cranking big engines. With or without a compression release. If something has an electric starter there's really no logical reason to have a compression release strategy. I have worked on a lot of motorcycle engines and never encountered compression release on anything.
Most recent small 4 stroke engines have automatic compression release? Ok, I'll bite, identify some of them. Kawasaki? Techumsen? What?
Tecumseh is no more, but had ACR. Kawasaki has it. Some Briggs do too. So do Kohler. I posted a link to a kohler manual showing it. Some engines like the Honda XR400R and some Yamaha ATV engines have a spring loaded compression release right on the camshaft. When the engine stops, a spring moves a special cam to slightly open the exhaust valve. When the engine starts, centrifugal weights move the special cam, releasing the exhaust valve to run normally.
The 2010 Honda CRF450 has a compression release. The Honda GX160 engine has automatic compression release. The Honda XL500R has automatic compression release. The Honda TRX has automatic compression release when in neutral. Yamaha YZ250F has automatic compression release. ALL Honda EB series generators have automatic compression release.
Hit send too soon. Suzuki King Quiad 300 has ACR.
2009 Kawi KLX250 has KACR Honda HS621A Blower also has ACR.Kawasaki FH641V 21HP, FH680V 23HP, FE 120D 4 hp, FE170D 5.5hp, FE250D 9HP, FE350d 11hp, FC150V 5HP, FC 290V 9hp, FC420V 14HP, FB460v 12.5HP all have automatic compression release.
Honda GXV210 18hp has ACR Honda GX390 has ACR All Kohler Command singles, CH and VC series, 5-16 and 410-493 have automatic compression release. Virtually all OHV Briggs and Startton engines have ACR.(ALL Intek series for sure) All Briggs "EZSpin" engines had automatic compression release (of a different type)
That enough for you to believe it is not "esoteric"?
No, thats a lot. Guess I've just never encountered any of these. I'm presuming it's to make them hand crankable even though the displacement is higher?
replying to jamesgangnc, HalC wrote: My 1968 Bolens HD 1250 Had a 12.5 hp Wisconsin engine. It now has a 1968 14 hp Wisconsin engine. Both of these machines have compression relief by mechanically keeping the exhaust valve slightly open. When my compression release stopped working I had to loosen the spark plug so that the engine would start and then tighten it while the engine was running. It will start normally after the engine is warmed up. This is all explained in the manuals that I have from 1968.
HalC posted for all of us...
Another heart warming story from the heartland.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.