acceleration knock

[dhdey]

got a new to me 90 Prowler with 3.0 OMC and Cobra drive.
seem like a good boat but almost every time i accelerate from a stop or near stop it will knock pretty hard like hit a chuck of driftwood. then continue on no problem until i come to a stop or slow below plane speed. I'm thinking bad u-joint but i'm new to boats so any help i could get would be appreciated

 

[gm280]

:welcome: dhdey aboard to iboats. Great to have you join us...

First thing you need to do is determine if it is a mechanical knock or engine knock. You can get engine knock from pre-ignition or too far advance timing. If it sounds more mechanical, then I would certainly check the universal joints and replace if necessary. If engine knock, either retard timing or move up to a higher grade fuel or even both. But unless you can make the determination, that's really all I can think off presently... Post back with your findings and let us know...

 

[dhdey]

it is a mechinal knock not an engine knock. i'll pull off the leg and see whats going on. changed the oil in the leg when i first got it and came out clean so i dont think its in the gears(and yes i did it the proper way....good thing i looked it up!)

 

[Skutt]

Check your motor mounts.

 

[ruggles]

it could be the clutch dog disengaging and reengaging due to the shift cable being improperly adjusted. I've had that happen in reverse until I adjusted it

 

[dhdey]

so motor mounts seem good. i thought that maybe it was coming out of gear but it happens under near or full throttle, pretty sure it would blow **** up if that were happening

 

[Idlespeedonly]

Can you feel it when it happens?
Sounds like the clutch dogs in the drive like ruggles suggested.

 

[dhdey]

oh yea i can feel it, one solid knock/thud usually just before getting on plane on medium to heavy throttle

 

[Idlespeedonly]

What you are feeling is the clutch dogs slipping. You need to inspect the lower shift cable, and everything related to it. Before you damage it beyond repair.
If its not already to late. They cant take a lot of abuse.

 

[dhdey]

what a confusing read on how to adjust cables.. i'm pretty mechanically inclined but i'm super confused. guess i should just pull the leg and go from there. or maybe just drive it till she blows and get a mercruiser leg

 

[dhdey]

just a bit of playing with shifter i noticed that it goes into reverse as soon as i pull back but when i push it back to neutral it stays in gear till i bump it a little into forward, then to get forward to engage i have to be at 1/4 throttle. so def out of adjustment but do i adjust at lower or upper cables?

 

[bruceb58]

If its that out of adjustment, the lower shift cable is likely bad.

 

[dhdey]

i adjusted the lower cable at the engine side and everything seems to be good now. but havent had it out on the lake yet

 

[bruceb58]

Tilt your drive up and look at the cable housing where it enters the pivot housing. That is where they usually fail. If the cable housing looks like it is coming apart there, don't use your boat until you replace it. May already be too late. All it takes is a couple times where the dog teeth release under load and they get rounded off and won't hold anymore.

 

[dhdey]

everything looks good, cable actually looks fairly new. thinking maybe it was never set right in the first place, gonna go for a test on the lake this weekend

 

[bruceb58]

everything looks good, cable actually looks fairly new. thinking maybe it was never set right in the first place, gonna go for a test on the lake this weekend

On the very first cable I had replaced on my boat, I had to go back and readjust what the OMC mechanic had done.

Make sure you store your drive in the down position .Way easier on the bellows and that shift cable.