8.1 starboard down 200 rpm

[d. stevanus]

tryin to close a deal on a 2005 340 sportsman with 8.1's with 65hrs and v-drives. initial sea trial showed starboard engine down 200rpm compared to port side.. a cylinder appeared to be cool on the starboard engine.. compression was checked and up at 160 or in the norm im told.. they have since changed the injector and spark plug. they re sea trialed it and say it runs great but is still down the 200rpm at full throttle.. they did note today that the sparkplugs are not the recommended mercruiser plugs and are going to change all plugs tomorrow morning.. the marina mechanic noted the props were of a different pitch by a half... the surveyor i hired said sea ray does this to equal out the transmissions or something like that and says that should not affect rpm.. the marina thinks the 200 rpm is no big deal but the surveyor is of the opinion we need to have this fixed.. just thot i would throw this out there and get a few opionions or if this has happened to someone else...

thanks in advance

 

[mainstream]

Hello 200 rpms are nothing to be concerned about. And the pitch at wot could account for different rpms also was this by tach or their computer analog tachs can be off also. So I wouldn't be that concerned that's just me I'd be concerned with fuel usage being different I had rpm difference but 500 rpm and 2 gal more per hour it was my wires and a few fouled plugs just my 02 cents

 

[skolbe]

A dinged prop could easily cause that to happen. Of course other things could as well.

 

[my3sons]

Your surveyor is correct on the props, the left hand is 1/2" more pitch than the right, he is correct on why they are different, and he is correct that it shouldn't make a 200 rpm difference. You didn't say what the rpms were. WOT rpm for 370 hp base 8.1 engines should be between 4400 and 4600, but, as an example, it is not ok to have one running at 4400 and one at 4600. The load on them is not in balance, either due to a mechanical issue causing one engine to come up short on power, or a prop issue causing a drag on one engine or allowing one to overspeed (but that is not the case if it is within spec), or a combination of both. Many things can cause what you are experiencing, it may be simple, or it may not be. Did that "cold" cylinder come alive after changing the injector and plug? My opinion is it sounds like you hired a good surveyor, based on his impressions of the boat, he would be the one to know where to start looking.
Good luck

 

[d. stevanus]

Thank you for the replies....this is from the survey...port side at WOT was at 4800 rpm, temp161,oil psi 60.3 volts 14.2. starboard side at WOT was 4560, temp 158,oil psi 56.4 volts 13.9.

and yes apparently that cylinder they changed the injector an plug was up to temp in the last sea trial.. from what your saying maybe that port side engine is revving a bit higher than it should... not that i would be running the boat wide open very often...just want things to be right when your making a 100k decision...
thanks again to all...

 

[d. stevanus]

oh.... and props were fine at time of survey...

 

[nowakezone]

200 rpm between engines is nothing to chase if all else is found to be correct. You're in the zone for WOT on one, too high on the other. Maybe others can chime in on this but I never have a problem with WOT being a bit high for the same reason you stated, except when I'm making sure it runs at WOT I don't run at WOT. A higher number tells me the engine is not overloaded with too much prop or otherwise. My3Sons sounds way more knowledgeable than I, but if everything else on both engines is good, I wouldn't worry. Just don't run the engines above 4600. Easy peasy.

Aside: does it bother you at all that the fishbox opens from the outside in? We were set to buy a Sportsman but the deal fell through at the survey. We ended up going with the cruiser only because I'm mostly catch and release anyway and prefer to pull lures versus live bait so a fishbox and baitwell aren't necessary. A cooler is fine for a kingfish or grouper. I always had a hard time wrapping my brain around the Sportsman fishbox.

 

[d. stevanus]

200 rpm between engines is nothing to chase if all else is found to be correct. You're in the zone for WOT on one, too high on the other. Maybe others can chime in on this but I never have a problem with WOT being a bit high for the same reason you stated, except when I'm making sure it runs at WOT I don't run at WOT. A higher number tells me the engine is not overloaded with too much prop or otherwise. My3Sons sounds way more knowledgeable than I, but if everything else on both engines is good, I wouldn't worry. Just don't run the engines above 4600. Easy peasy.

Aside: does it bother you at all that the fishbox opens from the outside in? We were set to buy a Sportsman but the deal fell through at the survey. We ended up going with the cruiser only because I'm mostly catch and release anyway and prefer to pull lures versus live bait so a fishbox and baitwell aren't necessary. A cooler is fine for a kingfish or grouper. I always had a hard time wrapping my brain around the Sportsman fishbox.

thanks for the tips... the fishbox is the same on my 290 amberjack and i use it for rod storage and the kids noodles..lol.. were on the canadian side of Lake Erie so i keep a cooler on the swim platform with ice since were catching walleye and rainbow and usually dont get much over 30".. i like the livebait well station because we perch fish in the spring untill the walleye and bows come in july and usually go through 5-6 dozen minnow a day with 4 kids fishing off the back.. i love my amberjack but we sleep on the boat on the weekends and its tight for 4... the 340 sportsman should solve this and my 2 foot itis...

thanks again for the advice