Craftsman 7HP B+S Mower Low Compression.

[Oaken]

Hello all,

I have a 7.0 190cc push mower that doesn’t start. It has very low compression of 30psi. I went ahead and rolled the dice with a $8 head gasket and after torquing to spec, I still have the same compression numbers.

With the engine at TDC, there is no play in the valves nor gaps. They are seated correctly. Obviously I would need to do a cylinder leak down test but it seems like an awful lot of work for a mower than can be used for parts.

Is there anything I can be missing other than ring issues?

 

[tom3]

Lots of these later model engines have an internal compression release, compression check might not tell a whole lot. Look for easy spin starting or something like that.

 

[Oaken]

Lots of these later model engines have an internal compression release, compression check might not tell a whole lot. Look for easy spin starting or something like that.

Thats good to know. There is some resistance on the stater pull cord and it stumbles to run on starting fluid. Carb was also soaked in a solvent tank as well as the mower having good spark.

I read online these engines need a minimum of 60psi compression?

 

[mechanic mark]

post model xxxxxx, type xxxx, trim xx numbers from engine, valve settings should be in your engine manual

https://www.google.com/search?q=how...9i57j69i59.34134j0j4&sourceid=chrome&ie=UTF-8

https://www.briggsandstratton.com/n...ualSearch.html?searchrequested=128t02-1270-b1

 

[Oaken]

post model xxxxxx, type xxxx, trim xx numbers from engine, valve settings should be in your engine manual

https://www.google.com/search?q=how...9i57j69i59.34134j0j4&sourceid=chrome&ie=UTF-8

128T02 - 1270-B1 10042959.

Those are from the engine cover per se

 

[ILENGINE]

Have you checked the valve gaps to make sure they are within spec. Also when you roll the engine over are both valves opening the same distance or is one just barely coming open and closing really quickly indicating a camshaft lobe issue. I wouldn't put a lot of stock into the compression readings. I like to see a decent compression reading on everything that I work on but I worked on a generator last year that had like 5% lose on leakdown test, but only showed 5 psi on the compression gauge.

 

[Oaken]

Have you checked the valve gaps to make sure they are within spec. Also when you roll the engine over are both valves opening the same distance or is one just barely coming open and closing really quickly indicating a camshaft lobe issue. I wouldn't put a lot of stock into the compression readings. I like to see a decent compression reading on everything that I work on but I worked on a generator last year that had like 5% lose on leakdown test, but only showed 5 psi on the compression gauge.

Hello,

When I removed the cylinder head both valves and opened and closed but honestly I can not remember seeing if both valves opened the same distance or not. I’ll remove the head again today or tomorrow and check the valves.