Small engine compresion

[merc_man]

Workin on a snowblower the just seems gutless. Its got a 5 h.p. tecumseh. Thought id throw the compression tester on to see and got a low reading.

After i decided to check my blower and got this

So was womdering what is low for these small engines. I thought mine was mabe a little low too.

I know saw should be no lower then 130psi.

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[merc_man]

Also was wondering if the other blower might have a decompressor of some sort and why the compression is so low. I wpuldnt think it would have even ran like that

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[ANewSawyer]

Donnyboy, on Youtube, has a video on it. I think he said you should come up with about 100psi.

 

[Fish]

Hard to say, most of those have a crude compression release, which is why they never published compression values.

 

[Nitehawk55]

If it's only got 40 lb it's worn out .
Cheapest bet would likely be a drop on 6.5 they sell at TSC or Princess Auto .

I see a fellow your way has a McCulloch D44 for sale in Kijiji .

 

[merc_man]

If it's only got 40 lb it's worn out .
Cheapest bet would likely be a drop on 6.5 they sell at TSC or Princess Auto .

I see a fellow your way has a McCulloch D44 for sale in Kijiji .

I seen that. It would be a nice saw ro have. But not in my budget this time of year.

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[AVB]

I think your working on a with 4 cycler since still runs at 40 psi. Before writing off I would check the valve clearances as they probably too tight. And with a 4 cycler you will not get full compression until the engine at operating due ACR (automate compression release) are usually used to make starting easier.

 

[Fish]

Also, if it is due to actual low compression, a valve job would be in order.
If we are talking about 4 cycle engines...
Not sure what all of the engines discussed here....

 

[merc_man]

Also, if it is due to actual low compression, a valve job would be in order.
If we are talking about 4 cycle engines...
Not sure what all of the engines discussed here....

Yes four cycle engine. Its a tecumseh 5 h.p. on my sons snow blower. He is almost 13 and got into shoveling laneways and saved up to buy what was supposed to be a good snowblower for 150. When we got it, ther was no snow to test but fired up fine.

Really dont wanna dump too much more into it but wanna make it write for him. Guess if we do have to dig into this motor it will be a good way for him to learn what makes them tick.

But if gonna cost too much to rebuild i got a good friend ( my wood cutting buddy) that has an extra 5 h.p. motor he said i could have for it.

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[merc_man]

Do you guys think it would be worth rebuilding this motor. Iv never done one and not sure what it would cost.


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[dall]

have you done a leakdown test on it to see where it is leaking from ?

 

[Fish]

Pull the head, and take a look. Put up some pics. Probably a good valve servicing would get it purring good, as long as the cylinder looks ok.
Also find the model number on the shroud.

 

[merc_man]

have you done a leakdown test on it to see where it is leaking from ?

No i dont have a leakdown tester. Any way to do it without? Make my own tester?

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[dall]

do you have a insert where you can screw into the spark plug hole just hook a regulated air hose to the insert and you can hear where the leakage is if out the intake or exhaust it needs valves done if through the dipstick or breather hose its the rings

 

[rogue60]

As has been said most small industrial 4 strokes have auto decompression usually just holds a valve open for pull starting. Best case it just needs the vale clearances set (common)
If it needs more work is it worth rebuilding can it be done cheap well yes if you do the work yourself but it all depends on what you find wrong. The crank and connecting rod bearing faces are the main thing to look at as things like running low on oil can score these bad, if crank/connecting rod is good it would as you say be a good way for your son to learn what makes them tick.
You could probably get away with the basics a set of rings/ hone lap the valves and set the valve clearances few new gaskets new spark plug fresh oil clean the fuel system it can be done cheap if you look around for best price on the few parts needed and there are lots of how to vids and such on youtube.

 

[AVB]

No i dont have a leakdown tester. Any way to do it without? Make my own tester?

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Home made leakdown is fairly easy to make especially if the compression tester you have has detachable hoses. You get a cheap adjustable pressure regulator and a few quick connects.
Mine is setup to pair with compressor tester and uses its hoses and adapters so I can test various engines easily.

This is so you can start with zero pressure and gradually crank it up to no than 50 psi while listening for leakage. (Yes I know most commercial leakdown testers are calibrated for 100 psi but don't need that for small engines). Unless you a tester that a metered port and two gauges you will not get a percentage leakage anyway. You do want lock the crankshaft so the piston is 1/4" down pass the top of compression TDC. An engine with good ring(s) will send the engine spinning the crankshaft. This way you eliminate the possibility that ACR is actively bumping the valve open. As you gain experience using the home made tester you will learn that you will not even need 50 psi to test for leaks.

As has been said most small industrial 4 strokes have auto decompression usually just holds a valve open for pull starting.

Doesn't hold the open for pull starting; just a monetarily opening (bump) just as the piston reaches TDC compression stroke. If the ACR held the valve open you never start the engine as it would have no compression. Even those engines with manual ACRs it is a metered release.

do you have a insert where you can screw into the spark plug hole just hook a regulated air hose to the insert and you can hear where the leakage is if out the intake or exhaust it needs valves done if through the dipstick or breather hose its the rings

Correct except when testing OHV engines as a blown head gasket can also leak through the dipstick or breather hose; hence, the reason for the valve cover removal on the OHV engines so can listen at the push galley.

 

[Fish]

What engine is it? That would be helpful.

 

[AVB]

Should H50 series (Probably the Snow King HSK50).

Here is a picture what I was referring as my home leak down and compression combo that I use.

Note the all important 10mm adapter in the lower right for the new trimmer and blowers. Also note the adjustable regulator has a right to left flow direction. Not pictured is the hose without the check valve for the leak down test but is the same the one picture; just forgot put it on the table. Using the hose with check valve will prevent the leak down working.

 

[Fish]

To be clear, explain the procedure of testing for leaks on a 4 cycle, what it entails, what you are looking at and why. Also explain how/why it is different from a crankcase leakdown test on a 2 cycle engine.
Also tell these guys of the dangers that they may encounter, they don't want to lose any fingers.......

 

[Fish]

Generally, low compression comes from leaking valves, in a 4 cycle, single cylinder..
But, in giving any/much help, it is good to know which engine model you have.
Once given a proper valve job, compression readings will go up to where they need to be.
But the success of such a job, hinges on the condition of the piston/cylinder, as reaching the proper compression could augment other problems with the piston/cylinder, and
blowby would become the major problem.
So in general, I just pop the head off and take a peek.
If it happened to be an OHV, I would do other things, so knowing what engine you have would be nice......