Cracked Inner Transom assembly while installing new assembly---Need advice
 

Hi guys,

While installing a new transom assembly yesterday, I cracked the inner transom assembly while tightening the nuts. I pulled the inner nuts down first and then the two on top and two on bottom. When everything was snug I proceeded to torque them to the spec of 25 ft. Lbs. Before the 25 lbs torque spec was met, the two lower holes cracked. I pulled the assembly off and noticed that the backside of the inner plate is not completely flat when a straight edge is layed across it. The original one is the same way so it is designed this way so this taper must be built into the transom when the boat was built.

Does anyone have any recommendations to keep this from happening again? I did not over tighten them and I was probably around 18 lbs when they cracked. I removed the assembly and scraped the area on the transom to make sure there was not some type of imperfection causing the issue.

Thanks for any advice.

Here are a couple of thoughts. Since your just started this I would take the transom assembly off and measure the thickness of the transom where all the bolt holes are. This will tell you if there is a taper for sure. Another thought is maybe the transom at the bottom is wet at the bottom, which is why the lower bolts would not torque down.

the back side of the inner is not completely flat cuz you torqued it onto a bad transom and it bent and cracked. the old one bent slowly over time. you put it on and tighten it it will probably crack too. i just checked one of my old ones. one side perf straight. other side slightly bent in by lowest bolt hole. i think you need a transom...

+1

Are your sure you arent squishing a transom that is rotted?

Transom plates are thin aluminum and over torquing will easily crack them. Most times it is a bad transom that is not supporting the plate though. I have had good boats that did it too though. Sometimes the holes drilled for the assy are to close to the cutout in the transom. If this is the case even if the transom is good there will not be adequate support for the plate if you start wrenching down on it really hard.

That said, I'd start looking for moisture before I bought a new plate!

My experience says soft transom also!
Sorry, hope im wrong...

You should be able to torque that inner plate to 500 ft lbs and it shouldn't crack, IF the transom is flat and solid. A tapered transom won't matter either, IF its flat. Your transom should be same thickness within a given area. There are specs in the mercury service manuals noteing the tolerances.

I agree with the census, check your transom for softness allowing it to squash under torque

If transom is good - possible uneven inner as thickness is not the same thru the area.

Run a 3 foot straight edge all over the inner section of the transom just to make sure. It would not be the first time that a boat manu was off in areas of thickness. .

Mercruiser specs the - Transom Thickness is 2 inch min to 2.25 inch Max and no more variations that that.

Outer surface of transom must be parallel within 1/16 of an inch in area covered by the transom plate and remain within transom thickness limits.

Inner surface of transom must be parallel within 1/8 of an inch area covered by the transom plate and remain within transom thickness limits

Transom plate covers 8 inches to either side of the vertical centerline.

inner transoms don't wear out and don't really show. they are cheap on ebay. try a big bolt and washers on lower holes. tighten snug and measure. then tighten down and see how much transom compresses.