Exhaust Manifold Torque Numbers

[RomanRegal]

HI, I have a 1987 Mercruiser 350 S/B 260 HP. I have replaced the Exhaust Manifolds and risers. From the search of the forums, I found the toque values for the exhasut manifolds at 20lbs. Is that correct?<br />Thanks Roman

 

[KaGee]

Re: Exhaust Manifold Torque Numbers

I thought it was more around 30-35lbs.

 

[Northern Eclipse]

Re: Exhaust Manifold Torque Numbers

My Merc manual says 20 ft lbs

 

[yoced]

Re: Exhaust Manifold Torque Numbers

Bolt torque is determined more by the grade of steel used in the bolt/stud than the needs of the particular application. If the application needed more torque then a better or bigger bolt is spec'd.<br /><br />In 1987 most bolts on the market were grade 2 plated; 20 ft lbs was called for in manuals that were based on that reality. Nowadays most bolts are grade 5, and 30 to 35 pounds is fine for a 3/8 diameter bolt.<br /><br />"About that tight" will work in most cases, especially if you are willing to go back and re-tighten after initial warm-ups.

 

[RomanRegal]

Re: Exhaust Manifold Torque Numbers

Thanks very much for the reply. Could I change overthe bolts to grade 5 from grade 2. Thanks again! Roman

 

[yoced]

Re: Exhaust Manifold Torque Numbers

Surely.

 

[90skichallenger]

Re: Exhaust Manifold Torque Numbers

I would actually highly recommend it. When I rebuilt my motor I replaced them with a grade 5. Also put some anti-siexe lube on the bolts when you put them in. and remember to retorque them after about 5-10 hours of use.<br />Later