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Hello, can you please provide the engine model and spec numbers? Thanks
Model: 28D707 Type: 1126-E1 Code: 971013ZB
Is that all the info you need ?
OK, for that model, there is not a thicker gasket offered. What I have done in the past with problems like this is to get a piece of copper that is .010" (.25mm) thick then take a marker and trace the gasket onto the copper, cut it out and use it along with the original gasket as a shim. This will lower the compression enough normally to do the job. I have never had to use thicker than that, but if the builder machined the head too much, you may have to use a second shim gasket. Thanks
What about grinding & polishing our the combustion chamber in the alloy head to lower the compression ratio slightly. Is this a logical option, or should I stick with putting an extra shim gasket in as you suggest ?
You could grind the head out. It would be a gamble as to how much to take out without making it too thin and waiting for it to crack. These heads are no longer available new. An advantage to using a shim, as the engine begins to wear and gets weak, you can remove the shim to boost the compression back up again. You couldn't do that if you grind it out. I would go with the shim, as that way you have not altered anything that cannot be undone. Thanks
Good suggestion ! One last question. What would the original design compression ratio be on that particular B&S engine, and what typical PSI reading would you expect on a cranking compression test ? I can probably calculate the shim thickness required, once I know the compression ratio & calculate the difference in original & oversize swept volume. Thanks !
Ok, the flat head engines like yours are typicaly 6.5:1 and should yield aroun 120 lbs of compression. Thanks
Many thanks ! I'll get to it in the next week or so, and see how I go.