Small engine compresion

[AVB]

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.......

Difference 2 cycle and 4 cycle is that with 2 cycles your looking for air leakage in the crankcase seals IE gaskets, mating surfaces, seals and intake boot or carburetor adapter and require block off plates for both the intake and exhaust ports. With 4 cycles your looking for leaking valves, head gaskets, cylinder and ring wear. You DON'T use the following tester on 2 cycles. Also on 2 cycle a vacuum crankcase test should be preformed.

As for dangers with the tester use is the use of too much pressure which on 2 cycles you don't use the following tester as it will blow a seal at minimum or worse. With besides the use too pressure is the rotational hazard especially if a blade is involved. Flywheels can cause serious injuries too if they move and your fingers or loose clothing is caught by them.

The following is from the Briggs and Stratton Service Manual on leak down testing. Although it says lock at TDC compression due the way ACRs are timed it should be done with the piston down 1/4" pass TDC. Also as mention if the OHV engine is involved you want to remove the valve cover as leaking head gasket between the cylinder and push rod galley will sound like bad rings otherwise if just listening at dip stick tube or breather tube. A good example is the Briggs 210000, 280000, 310000, and 330000 head gasket that are bad about blowing between the cylinder and push rod galley.

 

[Fish]

A quick/easy test that I do on some of the OHV engines, I take off the valve cover and start the engine and run on low rpms.

 

[merc_man]

Its not an OHV motor.

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[Fish]

Do you have valve tools of any kind?

 

[Nitehawk55]

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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Valve clearance would be worth a look also check for a blown head gasket .
Pull the head and if the piston is washed clean you know it's drawing oil up top which isn't good.
To rebuild would cost more than it would to buy one of the replacement 6.5 engines .
The cylinder will be egg shaped from wear and would have to be bored oversize by a machine shop to fix that then even finding an OS piston for a Tecumseh engine would likely be hard to find .
Some lapping compound can usually get the valves to re-seat without too much trouble .

 

[merc_man]

Thers a couple pics. I think ill start by checking the valve clearance and mabe relap the valves if needed

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[Fish]

Hell, just pop that head off and take a pic. Mail your valves to me, and I'll cut them for free.

 

[Nitehawk55]

This might be what you want , offer $75 and make sure crank shaft is right size .
http://www.kijiji.ca/v-cars-other/l...ne/1225339863?enableSearchNavigationFlag=true

 

[jake wells]

those H50 Tecumseh engines had a problem with loose valve seats or pitting on the exhaust valve.
but usually they would chuck a rod before they ever get that worn.

 

[merc_man]

Sorry i took so long to get it apart and look. I think it looks like the valve on the intake side is buggered. What you guys think?

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[merc_man]

Also with piston TDC and valves closed i can spin the exhaust valve and not the intake.
Never checked with feeler guage to see what gap was.

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[merc_man]

I must be loosing compression out the exhaust valve.

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[merc_man]

I took a light out to get better look at the intake valve. Its fine just had a little carbon build up witch looked like it had a groove in it but wasnt. Clean it with a rag and looks good. Will have to get some new gaskets for it and check gaps and probly have to take some off exhaust valve stem.

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[AVB]

Also with piston TDC and valves closed i can spin the exhaust valve and not the intake.
Never checked with feeler guage to see what gap was.

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I must be loosing compression out the exhaust valve.

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So now that you found your problem. Now do your have the tools to remove the exhaust valve so you can squarely file its stem down until you get the correct clearance?

 

[merc_man]

So now that you found your problem. Now do your have the tools to remove the exhaust valve so you can squarely file its stem down until you get the correct clearance?

Yes i have to install/ removal tool.

Was also wondering if this motor would have a cOmpression releas that may lift the valve at TDC?

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[AVB]

Yes it does have an ACR it usually bump the valve a few degrees before TDC compression and not at exactly TDC though it can affect the valve if the clearances are at zero which why most ACR engines valve clearances are checked with the piston at 1/4" down past TDC compression.

 

[Nitehawk55]

Looks pretty good , not much oil wash on the piston so the rings/cyl wear look to be good .
Lap and clean up those valves set to proper gap and I think you'll be good to go .

 

[Fish]

Check with a feeler gauge, you will see a bit of block warpage, and the exhaust clearance will be too tight. As that happens. Recutting the valves and seats are the best repair,
lapping is just a band-aid...

 

[merc_man]

You think ill have to lap them. I will have to pick up some lapping compound.

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[Fish]

The reason that you will have to take some off of the valve stem, is because the block warps away, and the seat is closer, but then the seat will be "cocked" and not seal..