HELP - engine mounts breaking drive bolts???

warrior-p · Post by **warrior-p** » Sun Aug 08, 2010 8:50 pm

The attached two pictures are of my engine mounts for the zz502, stinger drive and 3 blade sw sensencih. I am using 1/2" grade 8 bolts to mount the engine and drive. I have not had any problems with breaking bolts, but my partners boat who is identical in mounting desing has.

He has a Felber 598 with stinger drive and 4 blade superwide. We originally sheared off the 1/2" bolts and replaced them with a grade 8 5/8" diameter shank bolt and made sure the bolt shank was inserted all the way thru the hole. We broke the 5/8" again this weeknd.

What do your engine mounts look like? Has anyone had this problem? Any recommendations?

yobee · Post by **yobee** » Sun Aug 08, 2010 9:33 pm

Only thing I can think of is forward thrust over time is going to continue to shear the bolt until you go really big! A common design I see is setup similar to how it would be in a car... the clamshell type bracket on the engine over a "pipe" type bracket on the engine stand, with no room for forward movement at the engine without breaking the engine stand or bracket completely. What's that old sayin about something is only as strong as it's weakest point? Well you've found yours. Without redoing anything major I would at least drill it out for the biggest bolt you can fit that is for sure, or maybe a 2nd or 3rd bolt in there would help? Room? I don't know Im not there, but hope those ideas help, or maybe provoke the thought in someone else to help you better lol.

By the way that big inch felber motor and 4 SW blades ain't no punk....

JAMES · Post by **JAMES** » Sun Aug 08, 2010 9:41 pm

IVE FOUND ALOT MORE PEOPLE USE CONE STYLE MOUNTS THEY WONT DO THIS FROM WHAT IVE BEEN TOLD

goldhunter_2 · Post by **goldhunter_2** » Sun Aug 08, 2010 11:18 pm

well form what you said your buddy has a little more muscle with that fourth blade then your boat so the shearing problem would show up on his first , not to down grade the work on the mounting brackets But it appears the design is for them to sit flat on each other thus transferring 100% plus of the force to the four mounting bolts only. in my mind a cone or a angled type bracket that forced the brackets to bit down under load would be stronger then ones like this that force the bolts to take the beating

Smuggler · Post by **Smuggler** » Mon Aug 09, 2010 7:34 am

I would try to move things around where I could get 2 bolts in each of the front mounts. That still probably won't cure it but it's got to help! The cone mounts these guys are talking about are the ticket but that would require a new engine stand

emmitt Kelly · Post by **emmitt Kelly** » Mon Aug 09, 2010 2:37 pm

check out my pics ..this is how Bobby put it together in 1999

vacrin · Post by **vacrin** » Mon Aug 09, 2010 3:41 pm

Warrior-P is referring to my boat but it's the rear bolt on the left hand side (if you're looking at the back of the boat) that is mounted thru the stinger drive that has snapped twice. The first was a 1/2" bolt then I replaced it with a grade 8, 5/8" bolt which broke this weekend. From what we have deduced it's the bolt that is taking the brunt of the force from the prop when torque is applied. We've got some ideas for a solution but any ideas would be appreciated.

emmitt Kelly · Post by **emmitt Kelly** » Mon Aug 09, 2010 3:57 pm

just a thought...

Is the hole from the gearbox through the engine stand aligned?

Making sure there is no undue force pushing bolt in causing a side loading of the bolt?

of course I have never had any dealings with that much power. My engine is box stock.

40 years ago at Lockheed... No force allowed..undue stress from mismatch and poor alignment comes back to bite you.

Smuggler · Post by **Smuggler** » Mon Aug 09, 2010 8:55 pm

If its breaking the rear bolt I would for sure add the 2nd bolt to each side of the front mount. I think there is to much give in all the mounts leading it to break the weakest link..

hmgm123 · Post by **hmgm123** » Mon Aug 09, 2010 9:06 pm

That mount is mickey mouse for that motor. Do yourself a favor and modify that with cone mount like panther has on their engine stand. You could end up with a catastropic event like motor, gearbox,prop, cage, stand and hull all torn to pieces. I seen it happen and could total a boat.

dantheairboatman · Post by **dantheairboatman** » Mon Aug 09, 2010 9:37 pm

i agree with others as well. the bolts are in a dead shear. lots of guys with this power level with out issue and they are running the conical bushings setup. lots of guys use a horizontal mount for engine. good luck Darrin that should fix it.

Bob Burnside · Post by **Bob Burnside** » Wed Aug 11, 2010 10:29 am

I would think you could weld or bolt a gusset on the front of the motor mount down to the gusset on the engine stand. That would stop forward movement.

warrior-p · Post by **warrior-p** » Wed Aug 11, 2010 3:56 pm

dantheairboatman wrote:i agree with others as well. the bolts are in a dead shear. lots of guys with this power level with out issue and they are running the conical bushings setup. lots of guys use a horizontal mount for engine. good luck Darrin that should fix it.

so are your recommending to change out the rear to the vertical conical bushings only or do both?

how many 700+ hp motors and boxes have you seen mounted with the conicals? I plan on upgrading my motor this winter and do want the same thing to happen.

After reveiwing the break on the bolt, the bolt is tearing itself apart in tension along with a forward shear load from thrust. Primary failure was tension - thats a bad motor

warrior-p · Post by **warrior-p** » Wed Aug 11, 2010 4:04 pm

emmitt Kelly wrote:check out my pics ..this is how Bobby put it together in 1999

What does the gear drive or belt drive mount look like?

ps - thanks for the pic

goldhunter_2 · Post by **goldhunter_2** » Wed Aug 11, 2010 4:25 pm

The cone or angle mount will bit when the engine torque or thrust starts pushing against it instead of trying to make the bolt hold the load and shear it off

mudkat · Post by **mudkat** » Fri Aug 13, 2010 7:09 pm

I don't like the fact that all the bolts just through the plates with no support front to back maybe weld a plate on the front up from the bottom past the top of the mount and put some rubber between it and another bolt through it horizantlly.

rbjscott · Post by **rbjscott** » Sat Aug 14, 2010 12:24 am

Loose bolts break. If you are clamping a rubber bushing or shim, the bolt will always become loose. I would put a metal shim in its place. Unless you have 2 rubber shims it is solid anyway. If it does not break bolts you have an answer. A friend has the same problem with 383, we stopped it with a bump stop.

warrior-p · Post by **warrior-p** » Mon Aug 23, 2010 6:19 pm

rbjscott wrote:Loose bolts break. If you are clamping a rubber bushing or shim, the bolt will always become loose. I would put a metal shim in its place. Unless you have 2 rubber shims it is solid anyway. If it does not break bolts you have an answer. A friend has the same problem with 383, we stopped it with a bump stop.

Bump stop? in other words a stop to restrict the front to back movement or the twisting?

I now broke bolt off this weekend on my zz502. I feel it is the twisting of the mounts where the left side (side that breaks) is raising up where the other side is compressing when the motor torques up on the throttle snap pulling the bolt head. Do you think going to the cone mounts on the front will eliminate the problem where the cone mount places the motor parallell to the motor and better supports the bolt?

rbjscott · Post by **rbjscott** » Mon Aug 23, 2010 9:07 pm

I would mount the engine, thenjust place a spacer under Gear to see if it the stand is parallel to box. You are looking for 1/32 or less. I would shim for parrallel. Check and see if bottom bolt landing is flat also and parrallel . Also needs to be level with Gear mounts, front to back as well. And are you using thick flat washers that won't "cone" or bend when tightened. Hope this makes sence.

red_neck191218 · Post by **red_neck191218** » Mon Aug 23, 2010 9:09 pm

IF you don't want to change too much from the setup you have you could try a true Dynafocal mount off of a O-540 that would isolate the front mount in rubber top and bottom it should work as long as you used a hard plastic mount for the gearbox. There are better ways to mount the front but that would be the easy route w/ your setup.

rbjscott · Post by **rbjscott** » Mon Aug 23, 2010 9:12 pm

Yes a bump stop is to stop forward motion, but not tie engine down.

warrior-p · Post by **warrior-p** » Sun Aug 29, 2010 3:11 pm

After reviewing the century drive installation instructions, they recommend a spacer on top of the bolt, between the drive & mount and on the bottom which dampens the impact when accelerating. It also explains that my design is allways loading the bolt up as you described above. here is the installation instructions from a belt drive:

Step 12: The rear mounts of the Drive Unit main case should be sandwiched between neoprene. This is
accomplished with a long 9/16" Grade 8 bolt, a large flat washer and a 3/8" thick neoprene rubber
pad being installed from the top. A 1-1/2" thick neoprene pad should be directly under the Drive
Unit case between the case and the engine stand. Under the engine stand, use another 1-1/2"
thick neoprene pad, large flat washer, lock washer and a 9/16" lock nut (or use two (2) nuts to jam
nut secure). You will need a total of three (3) neoprene rubber pads per each bolt for the rear
mounts being a total of 6 pads. Century Drive Systems Inc. does not supply this hardware or
neoprene pads for the rear mounts since so many different mounting frameworks are used.
Remember for proper alignment that the 1-2" thick neoprene pad under the drive unit will compress
approximately 1/4" to 1/2". This compression will vary depending upon the density of the neoprene
pads being used. We suggest using medium to stiff Neoprene pads.

warrior-p · Post by **warrior-p** » Tue Aug 31, 2010 3:59 pm

After discussing the mounts with the energy suspension engineers this week, I will be installing the 9.4101 suspension on the drive mounts tomorrow night and will probably add a rubber isolation and sleeve to the front mounts as well.

warrior-p · Post by **warrior-p** » Thu Sep 02, 2010 1:48 pm

Got my new Energy Suspension 94101 universal mount installed mine last night as shown in the pics so we are going out this weekend to see if we can break it. If I was building a new boat, I would go with the Energy Suspension 94102 universal mount but i chose this for size constraints.

cbowjones · Post by **cbowjones** » Thu Sep 02, 2010 3:39 pm

Looks good Preston! Let us know how they hold up....hopefully it will be a solid fix!