Cylinder Head Bolts.-

[Sea Rider]

Need to replace all 10 cylinder bolts on a Tohatsu OB, are completely oxidized, rusted, although could be cleaned would preffer going for new ones. Was wondering if it''s ok and safe to instal SS ones as opposed to standard ones which seems are cast iron. Any thoughts ?

Happy Boating

 

[Scott Danforth]

stainless has very little strength compared to steel. most likely they were coated 10.9 (grade 8 equivalent) depending on the size, you could look for some 17-4PH stainless bolts which are almost as strong as 10.9/grade 8. they will rust eventually, however last a lot longer than standard bolts. be prepaired for the price.

Personally, I would use the stock bolts and coat with boeshield, fluidfilm or tefgel

 

[Sea Rider]

Thanks Scott

Yep, the bolt store told me what exactly you have posted about SS bolts. OEM bolts are impossible to get , will need to be imported and that's the route don't want to follow, will stick to what can be found locally.




Have bought 10 standard dark color fully threaded ones grade 10. Don't know the grade of OEM ones. What could happen if installing bit higher grade head bolts than OEM ones, say 10 grade instead of 8. The torque factory spec for head bolts are 25-26 Newton Meter. Old ones were founded excessively rusted due to an old head gasket failing over time. Will be assembled with a light coat of OMC triple guard grease, have worked fantastic well on previous powerheads when removing head bolts to change cylinder gasket

Happy Boating

 

[Chris1956]

I would recommend permetex #2 or #3 on the threads of those bolts. That should seal them against corrosion.

Two notes: The better grade steel bolts do not rust as much as the lower grade bolts, which is good. Also, high grade steel bolts used on aluminum threaded holes produces less corrosion (on the inside), than SS bolts used in aluminum threaded holes. SS and aluminum can really get stuck together.

Of course, the steel bolt heads rust faster, but you can spray them with corrosion guard or the like.

 

[Sea Rider]

Thanks Chris,

Good to read that the higher grade are better than SS or lower ones. No permetex available down here. Will have to stick with OMC Triple Guard Marine Grease for the moment. You should re torque new head gaskets back to specs at say 15-20 worked hours, will have less seizures, corrotion on bolt threads and a Long Live the Head Gasket as well.

Happy Boating

 

[Scott Danforth]

Permatex #3 is also aviation gasket sealer. Available at Napa under Napa gasket sealer

 

[Sea Rider]

Cleaned all bolt's threads inside powerhead to immaculate cond. Now you can screw bolts with hands near fully in.



Both mating surfaces were cleaned to smooth perfection, installed a new head gasket and torqued it to 25 NM. A slight coat of OMC Triple Guard Grease was used as of previous OB restorations. This weekend combo should see water again...Thanks Scot and Chris for the tech feedback, highly appreciated, served me well.




Happy Boating