Timing Cover Bolt strength

I need to install an engine plate that is tied into just the four lower timing cover bolts. The cover is a one piece marine setup (Nicson) that uses the upper portion of the cover to run a marine water pump. The cover has a provision to mount a lower plate on to the front of the timing cover.

First question....

Are the 4 5/16 bolts sturdy enough to handle the stresses of the engine weight and torsional twisting?

Second....

If not can the block be bored and tapped for a larger bolts/studs? Say 3/8's. Is there enough meat in the block to do without weakening it and has this been done before?

Thanks for your help.

Use Grade 8 bolts and a torque arm on the left side.

I've owned several bbf boats and used several of those covers. The only way it could be an issue is if one has one of those crappy 1/8" rear plates....otherwise there should be little to none 'torsional load' on it. If other things are correct it is ~ just holding the front of the engine up.
Like Rick said, use grade 8 bolts.

Lem Evans wrote:I've owned several bbf boats and used several of those covers. The only way it could be an issue is if one has one of those crappy 1/8" rear plates....otherwise there should be little to none 'torsional load' on it. If other things are correct it is ~ just holding the front of the engine up.
Like Rick said, use grade 8 bolts.

Will do on the grade 8 Bolts. I'm going to be building a 3/8th thick rear and front plate and fabricating a removable aluminum cover for the flywheel.
My concern had been the four small bolts. Thanks for the sage wisdom...!

How much power are you targeting? In the majority of cases, quality 5/16-18 bolts will be adequate as long as the rest of the engine is mounted adequately (as Lem said).

To answer your other question: we have opened up every 5/16-18 front timing cover bolt hole to 3/8-16 in these blocks without any issue whatsoever. Usually for the front engine plates that use only the lower 4 bolt holes (as you intend), we tap those bolt holes to 3/8-16 and install studs. NOTE: The bolt holes in your Nicson cover are 0.375" (3/8") and so you might need to enlarge them as well in order to allow for crankshaft seal alignment if you step up to a 3/8 fastener down there.

Paul

Thanks Paul, ballpark.... around 650 700 hp. Nice to hear that it's been done before and that there is some meat in the block to upgrade the four lower fasteners. I figured the cover would need some TLC, I always look at modifications as a whole so I wanted input from the masses. As Lem stated the true clamping force is in the rear plate assembly. The front is mostly along for the ride and splitting weight support duties.

What my main concerns have been is loading and unloading of the engine when the prop bites and then unloads due to water conditions.
In a static or a constant load situation I'm sure the 5/16ths bolts are more than enough. The 3/8ths studs will give me more confidence when it comes to on-off shock loads constantly transmitted through the drive train.

Thank you all for your insight.

Paul Kane wrote:How much power are you targeting? In the majority of cases, quality 5/16-18 bolts will be adequate as long as the rest of the engine is mounted adequately (as Lem said).

To answer your other question: we have opened up every 5/16-18 front timing cover bolt hole to 3/8-16 in these blocks without any issue whatsoever. Usually for the front engine plates that use only the lower 4 bolt holes (as you intend), we tap those bolt holes to 3/8-16 and install studs. NOTE: The bolt holes in your Nicson cover are 0.375" (3/8") and so you might need to enlarge them as well in order to allow for crankshaft seal alignment if you step up to a 3/8 fastener down there.

Paul