18 hp briggs and stratton smoking

[Trapper Dano]

This is normal operation, if I understand what you are asking. When the rocker arms are "up" the valve is closed. On the compression stroke, both the intake and exhaust valves are closed (thus both rocker arms are even); otherwise you will have no compression. The other cylinder will be on a different stroke (say intake for example) which requires the intake valve to be open and the exhaust valve to be closed. When a valve is closed there is a small amount of play (clearance) in the valve train which allows you to spin the push rod and will allow for some slack in the rocker arm.

The smoking problem is likely not related to the valve train based on your description. If the oil level was too high and had gas in it you need to look for a problem with the carb (flooding and dumping fuel in the intake) or fuel pump if it has a vacuum driven pump. It can have an internal failure and gas can be drawn into the vacuum line and into the engine. You changed the oil and the oil level is good. I would clean the oil out of the intake, make sure the spark plugs are good and run it for a while. Keep an eye on the oil level. If the oil level stays where it should, but the engine keeps smoking, then dig further.

What color was the smoke?

Just did a compression test on the motor a hair under 90 on the front cylinder and about 165 on back cylinder? the smoke is white

[ARGOJIM]

Just did a compression test on the motor a hair under 90 on the front cylinder and about 165 on back cylinder? the smoke is white

Adjust the valves, one may be too tight allowing some compression to escape. Redo test.


BTW when we bent a pushrod our machine smoked violently.

[Trapper Dano]

Adjust the valves, one may be too tight allowing some compression to escape. Redo test.


BTW when we bent a pushrod our machine smoked violently.

Checked the push rods they are all straight. picked up a feeler gauge but wont get a chance to work on the machine again until Thursday night likely, will check all the valves and set them all the same between .004 and .006 Correct?

[Trapper Dano]

Adjust the valves, one may be too tight allowing some compression to escape. Redo test.


BTW when we bent a pushrod our machine smoked violently.

Snuck out of work at lunch. Checked the tappets adjusted one a tiny amoumt all are .004 did a new compression test still 90 in the front cylinder and 170 in the back. Could it be my compression relief?

[Trapper Dano]

Got out to the garage tonight and pulled the head that had the head that read 170 compression. Took so.easy photos of the head and the valve springs and guide. I think it might be a valvr guide? Is there a way to post photos here?

[Trapper Dano]

Is there a way to post photos here? I pulled the head tonight that had 170 compression. I think it might be a valve guide? Would like to.post a photo so someone could maybe confirm. Never opened a small enginr head before so not exactly sure what it is supposed to look like.

[hipowerone]

You can add photos by "GO ADVANCED" option on a post, then scroll down and "MANAGE ATTACHMENTS" where you can "ADD FILES" and upload them to the site.

[dirtdobber]

Just curious.....why did you pull the head from the good side (higher compression side)?

[Trapper Dano]

Just curious.....why did you pull the head from the good side (higher compression side)?

One side was 90, and the side I pulled the head on was 170. When I did the pull the pull the plug wires test, unplugging the 90 cylinder caused it to run rougher, whereas unplugging the 170 cylinder caused no change to the way it ran. I thought that indicated that it was running more on the front cylinder the 90 one than the back one the 170? And isn't 170 too high? I thought I read that 90-110 was more normal?

[Trapper Dano]

You can add photos by "GO ADVANCED" option on a post, then scroll down and "MANAGE ATTACHMENTS" where you can "ADD FILES" and upload them to the site.

Thanks Hipowerone

[dirtdobber]

And isn't 170 too high? I thought I read that 90-110 was more normal?

I'm not sure what normal is for these engines, but 170 does seem high. If I'm applying the right logic, pressure and volume are proportional. With atmospheric pressure being 14.7 pounds, and assuming the pressure inside the cylinder on the intake stroke is 14.7, then then it has to compress 11.5 times to reach 170 psi. A good old stock Chevy small block engine would have somewhere around a 8.5:1 ratio, but I'm not sure what these engines should have. But, I can't think of anything that can go wrong and cause increased compression, unless maybe the exhaust valve is not opening and the cylinder is able to draw in a little more air than normal and thus is reading a higher compression (that's just a wild guess, by the way). Especially since the compression on one cyl. is nearly double the compression on the other. You did read your gauge right (psi) and not some other units??

Post some pics. Not sure if they will help but pics are always fun to look at.

[Trapper Dano]

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I'm not sure what normal is for these engines, but 170 does seem high. If I'm applying the right logic, pressure and volume are proportional. With atmospheric pressure being 14.7 pounds, and assuming the pressure inside the cylinder on the intake stroke is 14.7, then then it has to compress 11.5 times to reach 170 psi. A good old stock Chevy small block engine would have somewhere around a 8.5:1 ratio, but I'm not sure what these engines should have. But, I can't think of anything that can go wrong and cause increased compression, unless maybe the exhaust valve is not opening and the cylinder is able to draw in a little more air than normal and thus is reading a higher compression (that's just a wild guess, by the way). Especially since the compression on one cyl. is nearly double the compression on the other. You did read your gauge right (psi) and not some other units??

Post some pics. Not sure if they will help but pics are always fun to look at.

[Trapper Dano]

I thought the same thing that it was too high and had no clue how it could get that high. I retested both cylinders 5 times always got the same readings 90 in front and just shy of 170 in the rear cylinder. I too am baffled. I know very little about small engines but I think the head looks normal, doesn't look like any of the other ones I had been able to look up with head problems. The gasket is good, and I am able to hand compress both the springs and both valves open?

[ARGOJIM]

Stupid question did you have spark in both cylinders at the tester and the plug? a dead plug or burnt diode will cause poor performance and rough running.

Perhaps Nubs knows the rough compression readings.

[Trapper Dano]

Stupid question did you have spark in both cylinders at the tester and the plug? a dead plug or burnt diode will cause poor performance and rough running.

Perhaps Nubs knows the rough compression readings.

Yeah Jim i have spark in both, even put brand new plugs in it.