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Engine tear down, reassembly and tuning
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Retorque the head
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Install the spark plugs. They should be torqued 18 to 20 ft/lbs, but since the bottom one must be installed with a wrench this will be impossible. Rather tighten the plug until the gasket on it is snug. For fresh plugs it will be quite a bit of turning past finger tight - about 1/2 a turn. You'll feel the crush washer bottom out and the plug will become hard to turn. Stop there. For old plugs you'll have to use your best judgement. But be very careful as it's easy to strip the aluminium threads in these heads.
Run the engine in water up over the seam between the lower unit and mid-section.
After a couple warm up and cool down cycles, you'll have to retorque the cylinder head to 70 inch/lbs. Since the bottom two bolts are inacessable, you'll have to use an extension. A 7/16 combination wrench or 3/8-7/16 wrench can be employed with a 3/8" torque wrench, but the torque will be magnified. With a couple careful measurements you can torque these accurately.
Carefully measure the distance between the centre of a head bolt when placed in the wrench to the centre of the other end of the wrench. Mine measures 6.5".
Next measure the torque wrench. There should be a mark near the centre of the handle of the wrench. If not sometimes there is a differently knurled ring or some sort of indication. If none of that is present, make a mark at the centre of the torque wrench's handle. Carefully measure the distance between the centre of the square drive on the torque wrench and the mark or center of the marks on the handle. Mine measures 9.875 (7/8) inches. Now calculate the torque:
Setting = 70 inch lbs x Torque_Wrench_Length / (Torque_Wrench_Length + Extension_Length)
In my case:
Setting = 70 x 9.875 / (9.875 + 5.5)
Setting = 70 x 9.875 / 15.375
Setting = 70 x 0.642
Setting = 45 inch/lbs
So set the wrench to what you calculate, and then place the wrench on it's square drive. It is absolutely critical you then ratchet the torque wrench until the extension you've put on it appears to be straight with the body of the torque wrench, as it appears in the photo. Then simply torque the lower bolts.
I hope this can be of some service, and good luck with your 4hp! If you have any questions or comments, don't hesitate to email me at paul.moir@gmail.com.
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All projects on Shareaproject.com are user-submitted and should be used for reference information only. The projects are not intended to be complete "How-To" articles. Use the information contained in these projects at your own risk. Projects are not checked for completion, accuracy, or safety and therefore cannot be guaranteed in any way.
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