88 OMC Cobra engine/motor mount alignment

I had the engine replaced in my 1988 Larson/OMC Cobra 5.7 L about a year and a half ago. I was changing the oil the other day and noticed a large nut rolling around in the bilge under the engine. After some head scratching, I determined it was the top (jam?) nut off one of my front engine mounts. The nut on the other side was also backed off about three full turns. I would simply cinch them both back down, but I'm having planing issues (incredible long time to come up on plane, no matter where I set tilt/trim) and there is now a "rattling" noise in my outdrive. Might they be related? Is there any way to check engine/out drive alignment with engine installed?

Thanks for your help.

yes but you have to remove the drive and use a alignment bar. Can be had on ebay delivered for under 50 dollars.

May i ask what manual your using ?

I had the engine installed (actually 3 by the time they "got it right") at the local marina and had lost faith in them long before my latest (loose nuts) issue. I'm competent to change oil, but that's pretty much the limit of my expertise, and I have no manual.

Thanks.

Hmmm, sounds like the loose nuts were the ones who installed the engine. On the bright side, assuming the engine WAS aligned properly when it was put in, the lock nuts are not all that critical. The engine won't go significantly out of alignment without them. It is certainly a good idea to put them back tho. I like to smear the nuts and threads on the mounts with a good thick coat of grease to keep them from rusting. The consequences of misalignment are a blown out coupler, worn shaft bearings and noises.
As to the lack of power and difficulty planing, gosh, hard to say. So many ifs.

I didn;t ask what is your wot?

Quick history/details. My boat is a 1988 Larson cuddy, 5.7L OMC Cobra. I had the engine (which had at the time @ 1,700 hours) replaced about a year and a half ago, after detecting water in my oil. Three tries (2 complete engines) later, that issue seems to be resolved. If a slip slowly into the throttle, tach @ 2,000, then mash'er to the floor, she coughs (backfires?) a couple of times and eventually away I go. If I mash'er to the floor from a standing start, she sputters, coughs and will die. It appears to take @ 3 seconds for the primaries to open completely. Time for a carb rebuild? Any other suggestions for troubleshooting?

Your help is appreciated.

sounds like you need an accelerator pump... not sure I would do a carb rebuild if it runs well otherwise and idles ok...
seems like ethanol fuels are shortening the life of the cups on accel pumps.. I just bought a high volume one from Jegs...better..still hesitates slightly at throttle mash though...always hard to get a Qjet to pump enough on accel I find.

o2batsea said:

On the bright side, assuming the engine WAS aligned properly when it was put in, the lock nuts are not all that critical. The engine won't go significantly out of alignment without them.

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Respectfully but fully disagree.
Without the jam nuts, the lower nuts may have changed position, causing a change to the engine position.
Note that the OP says that this was over a year ago!
If so, the engine alignment may no longer be adequate, and premature coupler wear may have occured.
Not suggesting that it IS OUT OF ALIGNMENT..... but this would be a concern for me!

rshanor said:

I had the engine installed (actually 3 by the time they "got it right") at the local marina and had lost faith in them long before my latest (loose nuts) issue.

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If I were you, I'd document this by taking photos, and document another person's comments that they too had seen that these nuts had not been properly tightened.

If the engine mis-alignment has caused drive coupler failure, the engine must come back out for a coupler replacement.

Perhaps have a third party go in with a bore-scope and examine the splines.
Alignment can be checked at this time also.

If the coupler is failing, or has failed, you will not want this to be on YOUR Dime....... nor should it be on YOUR Dime!


Just my two cents on this!
.