why my engine vibration at 1000-1500 RPM
 

any ideal why my engine 350 with lt4 cam vibration at 1000-1500 RPM .engine only 10 hrs after re ring kit, new propeller, still vibration .thanks

Is it a mechanical/rotational induced vibration or a vibration as the result of combustion events (if that makes any sense)? Mounts loose, gimbals, prop shaft, unbalanced prop, prop pitch imbalance etc. In gear or out of gear? Need more details.

when the boat not in gear test it on my drive way with water hose, took it to the lake it is shanking at 20-30mph.i got no vacuum leak, (I check it with starter fluid )

Is the engine running rough- cam lope?

Check your mounts, etc. Is your u- joint coupling tight?

have you checked prop shaft runout

Was your motor rebuilt or taken apart if so - harmonic balancer did someone hit with a hammer for removal or reinstalling , is it in good shape regardless even if motor was not touched

Engine coupler warped - was it torqued down using a proper pattern and torque spec, or engine coupler loose - bolts backing out over time.

need more info plus was the motor rebuilt , is this boat a carb motor or Throttle body injection or MPI, If injected make sure the injectors are properly flowing and correct amount of fuel volume. On TBI engines it is really important both injectors need to match perfectly in spray patterns along with flowing volumes .

unbalance prop blade(s). As other mentioned put a dial indicator on the propshaft and rotate it to check run out.

next compression test solid and or solid leakdown test,

Next are all cylinders firing and have strong spark ?

Check your spark plugs and check them for any signs of water. We see so many improper winterizations that in spring time upon recommision this really causes poor running conditions and vibrations of the engine

I don't think lower unit or propeller
I test it run on my driveway with water hook up
engine idle 700 RPM when I rise up it star vibration to 1500rpm
spark plug new (color dart brown I took off when do compressor test)
compressor all cylinder 150psi only 2 cylinder -140ps
I did not do leak down test(will do )
I used carburetor elderbrock 1409(buy it on ebay)
any input please give thanks for help

same flywheel, same balancer? go back to basics...check firing order, replace dist cap.

need some more info. in your first post you say it has 10 hours since rebuild and still vibrates. did it vibrate before the rebuild or just since the rebuild. my guess is it has either the wrong flywheel or wrong balancer. it should be internally balanced so it would have a neutral balancer and flywheel but as it has been worked on there is the possibility that someone used the wrong one on either end.

the engine I remove from yard (2000 chevy van 3500) balancer same fly wheel used from boats
will check firing order

firing order 1-8-4-3-6-5-7-2 just check new distributor new coil

I was going to ask a couple of things but I've now lost interest with your problem...Good luck with your worn van motor in a boat........Don't mean to be a Richard ..but I am

try balancer that came with 2000 van motor. what year was motor came out of boat?

Not everyone that owns boat has a lot of money. I would assume that the used motor was all he could afford right now. We should still try to help him.

tk350....There are a lot of things that can be causing the vibration as was stated by others in this thread. Check to obvious stuff first (motor mounts, distributor cap, plugs, etc). Could be the harmonic balancer as stated previously as well. Is it backfiring, missing, coughing or anything? When you get above 1500 rpm does it smooth back out? We need more info.

Richard Motor can you tell us your set up and what your ride is and how well your app runs since you like to give some up here a hard time. Man cut some slack dude as it seems you like jumping on people. Do you even own a freakin boat.

OP are you asking what firing ordering is or just saying yours is correct ? You need to post as much info as possible about what U have done and what you have as far as set up. what ignition system are using ? Will have to say that a stock auto base engine will not give U reliability down the road if not sooner rather than later. What balancer are you using - How did you install the engine coupler, hopefully in a proper pattern and 3 pass proper torque spec, did you align the motor properly ? how is your U-joints, Do have solid spark firing on all 8,

Again you need to post as much info for the correct help so that people can help you correctly.

Last 2 BBC I had come in with 1500-2100 rpm vibration ,first had wrong flex plate, could see windshield shake from 1500-2100 rpm ,second flex plate backwards ,that one worse .yours prob runs te std trans style flywheel less choices theelieve .if someone slipped you a 305 crank (same casting part# as 350 bfferent balance and some lighter pistons ..well ..

I can spell I promise , Verizon hates me

I am not cheap for build engine
I was re build many engine for car and truck 5.7-4.3-3.8 even northstar 4.6 as myself
I never work on boats this is my first time
the boats I had 17ft long original 4.3 upper unit 1.84 ,I took engine out because it crack block when I buy, that why I went to yards get vortec engine from the van and it had 4 bolt main and it shown 84.000 mile on van .I took all the parts out I keep block ,piston ,rod ,crank, cylinder head.....the cylinder bore it not wear out to me crank I bring to machine shop they check out and polish for me, other wise I get all new part from summit and jeg upper unit I change gear to 1.47 with mercusier tools ,when I test the boat I few engine lose rpm ,and I find down engine shaking when I test run on my drive way, that why I go on line look help and learning more from here I try to up load some picture and video for your guys see only my English not much too explain for people understand here but I understand what you mean thank again

ok, so he has a 4.3 flywheel on the 350. and apparently the 4.3 balancer. is a 4.3 an externally balanced motor? it is a 350 with 2 cylinders sawed off the front, so maybe. if so balancer and flywheel are the culprits. i put a 400 small block in my antique sundancer trying to get over 35 mph. i bought a 400 flywheel which turned out to be 454 flywheel. just above idle boat shook so bad it looked like railings around bow were gonna break off. as far as richard is concerned, i never rebuild boat blocks. i always find one that spent it's life at 2000 rpm with antifreeze in it instead of a raw water-salt water full throttle engine. tk350, are you running the van cam? or did you get a marine cam? that wouldn't be shake problem, but giving away power using an emissions cam in a boat.

I do like to give my opinion, even if it doesn't agree with yours...Is that jumping ...Did you write that a van motor wouldn't be a good boat motor? Until the op explained ,I took it as he pulled motor from van and put in boat .Not that I should answer ,but yes I have and have always owned at least one boat, usually more...the last 40+ years. If you don't like what I post ...I really don't care....Don't worry ,be happy. I don't think I come off as the all knowing ,as you do...You can call me dic. Have a good day ,I will

Think he went with lt4 cam ,the ht383 cam might be a tad better ,but haven't seen a 4 bolt vortec block yet , even in the pcm motors . If this guy gets it right , a 300 hp 17 foot boat should be quite a sleeper.sounds like he's missing some flywheel weight .

dont know about all the 4.3's as some have balance shafts, some do not. the ones with the balance shaft I know are externally balanced. right now you need to pull the engine and get a balancer and flywheel for a 350. I would bet that fixes it.

Agree with last 2 replies and he had the crank out at the machine shop so he needs to try to balance it all. The 4.3 balance shaft came into play around 1993 model years before that Merc used fluid motor mounts to help. He needs to at least change the flywheel and hopefully he has the correct harmonic balancer. At least he is trying. Hopefully he doesn't mind pulling the engine again.

I think 4.3 v6 flywheel can be use on 5.7 motor,if I not right .Would you give me parts number flywheel for v8,it wont take too long to full the engine out .

i have a 4.3 flexplate sitting here and it has a huge weight added from the factory. also the balancer has twice the thickness on one of the three spokes so i would say neither of them would work on a 350. put a post in the wanted section and i would bet someone has the ones you need.

ok, just did some surfing in s10 forums and came across novak conversions which was talking about putting 4.3 in jeeps. in 86, when they offset cut the rod journals so it was an even-fire engine even though it was a 90 degree v6, they went to an externally balanced flywheel. that is ALL one piece seal 4.3's. the flywheel IS the culprit. but get rid of the balancer too. I have about 5 to 10 small block balancers that'll work with a boat. but the lower pulley will most likely bolt right on the 350 balancer that came with the truck. go to JEGS or Summit and order a 350 flywheel. only about 80 bucks. you wanna do ebay, find the right part number for a 1 piece neutral balance flywheel so you don't get sold the wrong one. what starter bolt pattern? A; one about as far forward from the other as they are wide apart and the both bolts same length? or B:both bolts next to each other with outer bolt shorter? if A it is 168 tooth flywheel. if B it is 153 tooth flywheel. you can use either flywheel, but you need the starter to match. some early mercruisers used a flywheel cover that won't fit over a big flywheel, but I think they were before the 4.3 existed. the one 4.3 boat I had was mid eighties and had big one piece flywheel. I just looked for that flywheel in garage but couldn't find it to check for the counterweight, but I think I remember it being there.