Volvo B151 Cylinder Head Repair (adding a ring to #4 Cylinder)
Several years ago the method of installing a steel ring was introduced to repair the last port on the Volvo 4 Cylinder engine. Although the ring has no special size most of them were made to small and they failed to make the repair last for any time. Unknown by most, the problem begins when the exhaust manifold becomes plugged and corroded at the waters exit, after hours of use and this allows water to be scavenged and lays in the #4 cylinder port. In saltwater we find it best to simply replace the exhaust manifold every 5-8 years instead of awaiting the problem. Of course flushing the engine after each use greatly helps this issue.
The link to the picture page below will show the procedure to install a steel ring into the last port. I made the tool from an old inboard 4" shaft coupler and welded a 1/4" piece of tool steel to a piece of shafting, ground it to cut a 2" hole. The depth must be determined by the damage. Also the rings OD could also be changed and made smaller but the smaller rings seem to have a short life.
Costs would depend on your finding of a good machine shop and even a better machinist with the ability to understand what's needed. Although the repairs pictured were made with the engine out of the boat, I have completed several such repairs without engine removal. On a couple repairs, an angle drill motor was used.
Today's costs (4/28/2008) on a new manifold is $407.00 list, our selling price with engines is $310.00 each. (I would rent the tool)
Good luck and please remember, it's only a repair. It will add time to your engine, how much time depends on the job you do and what shape your new or used manifold is in after ?? hours of use.