Logo
FULL SITE MENU

First run under load, ghosts appear; overheat,knocking and whines (resonates)

M

Mouse

Member
So i got my mercruiser 3.0 with alpha one leg all tlc'ed up, runs beautifully on the trailer.

First time at the jetty she was harder to start and eventurally gave up suspecting i flooded her. Pulled her out started her on the trailer,back home fired straight up.
(I know there two differnt playground for boat troubles)
Tried again the other day at the jetty,still hard to start but sucess!

Limped her around a little make sure she wouldnt cut out then went onto the plane for only about 300 - 400 meters in total.
She gave a couple of clacks/knocks at the start with a growing whined, pushed on for a little then backed back off the plane and she started to idle rough and i noticed the heat gauge had climb a fair bit (usually 1/3 unladen but now was 3/4) i didnt get a chance to pay attention to the rev gauge.

So back to the ramp and home.

I know the overheat is going to be a blocked manifold or screwed thermostat.
And i do have a crack in the lower housing along side the prop ( only an inch or 2 long) that could be causing knocks and resonating, just want to confirm a crack that small could cause these symptoms ? Before replacing the lower unit (500 - 2000! : ( starting to think ive bought a problem)
But also want to know what else i could do or look at to eliminate other causes before replacing the lower..
Also is there anything i may have missed ?

Action plan for now is;
Remove riser, mani,resivour - clean and regasket
Replace plugs because to be honest i should have done them before.
Contact a shop for 100 point inspection and possible consulting on housing repair if it can be done ?

Thanks in advance for any advice and wisdom
And i hope the speed im learning is leaving an impression
Still havnt got a manual
The rookie.:D
 
What year is the motor?
Did you check ignition timing?
Mercarb or Rochester?
How old is raw water impeller?
Get a manual if you plan on doing the work yourself.
 
Im not sure on the year (details are reasonably faded on specs sticker ) but serial number's 5600923
I havnt checked the timing, its not a job i wanted to rush into but should be done
Carb is a rochester
And ive replaced the impeller and the housing because prior to now shes been stored for 10 years or so

Do you know where i could download a free manual by chance ? I will buy one soon.
 
Last edited:
Yeah im working on it. Researched that the number's supposed to start with 0 so im going to have a look in the morning and post it up.
 
kimcrwbr1 said:
Did you check ignition timing?
Click to expand...

Mouse said:
I havnt checked the timing, its not a job i wanted to rush into but should be done
Click to expand...

Marine Engines undergo loads that are completely different from that of the Auto engine. These loads are heavy and are constant with NO coast time.
Because of this, Ignition Timing ...... aka Ignition Advance... becomes extremely important.

We do NOT simply set/adjust BASE or Initial advance and call it good! ,
We also must check the "Progressive" advance and the "Total Advance" at the RPM at which it occurs! (see your OEM service or work shop manual for these specs)

Excessive Ignition advance often results in a very destructive "Detonation" phenomenon.


.

 
Alright, due to the wear ive been getting the serial number wrong, found second plate still as faded but
Serial:6600923 - mercury 1985
HP: TH+
model: 1001705
Discription: thruster 2 TM/RC/RCL/T21/R21/RL21
 
I found a previous forum on here with the help of the year model and ive researched about detonation pre ignition and ignition timing.
New work list is;
Spark plugs
Fuel oil and inline filters
Carb
Water pump/cup
Wiring
Point gap
Thermostat
Exhaust water shutters
Starter ( bushes and armature )
Bendix gear
Distributer
Plug gap
And everything timing

Thank you all for your input
I posted my new work plans further suggestions/advice
Also dose anyone know a good source for an overhaul gasket kit for the 85 merc 470 ?
 
I am impressed with your enthusiasm but allways start with the most important things first. Get it running good then pick away at the check list.
What are your compression numbers?
Rebuild the carb
Allways set the points with a dwell meter first then set the base timing. Using a dwell meter gives you the best performance.
Map out the advance curve on the distributor. Like Ricardo said detonation can be fatal.
Monitor the oil levels close the first few times out looking for water intrusion especially in the drive. Engine oil should be checked prior to every startup.
Not a big fan on changing out good parts if it aint broke dont fix it.
If the ignition coil gets hot while the engine is running install a resistor wire to coil pos will keep you from cooking the points.
 
When dealing with a point ignition you should at a minimum,

Annually replace points, rotor, condenser.

But if you want to end this issue for ever there are electronic conversion kits that will eliminate the points and condenser for ever.

Pertronixs is one manufacturer....
There may be others.

You just swap the parts and reset timing and once done you will never have to do it again.
 
.................................


I agree with Kim.
At a minimum expense get this engine running and then see what other (if any) issues this engine may have.


Mouse said:
I found a previous forum on here with the help of the year model and ive researched about detonation pre ignition and ignition timing.
New work list is;
Spark plugs

Fuel oil and inline filters
There should be NO in-line fuel filter (the square area of filter media is far too small).
You should be using the Marine style cartridge unit or better yet, a RACOR unit!

Carb

Water pump/cup
Seawater pump????? Or engine circulating pump?????

Wiring

Point gap
Point gap is an estimate ONLY of correct dwell angle...... it is best to use a dwell meter!

Thermostat
Exhaust water shutters

Starter ( bushes and armature )
Bendix gear
I don't believe that the GM 3.0L was ever equipped with a Bendix style starter motor.

Distributer
Plug gap
And everything timing
Yes.... Progressive and TA.
See your OEM service manual for this info.

Thank you all for your input
I posted my new work plans further suggestions/advice

Also dose anyone know a good source for an overhaul gasket kit for the 85 merc 470 ?
If the 470 engine needs to be over-hauled, I would strongly suggest cutting your losses now.........., and find another NON-Merc 470 style replacement engine.
Click to expand...


FYI....... pre-ignition and Detonation are two entirely different phenomena !!!!!!




.
 
Last edited:
Thanks kimcrwbr1
I havnt done a compression test yet but i will put it on the list along with the carb : ).
Im likewise with if it aint broke dont fix it and get her enjoyable first and plod along with the rest but heres where my experiance shows..
Im not all that sure whats most important.
Im thinking timing, points and plug gap but in saying that not sure what to start with so i dont have to redo work cause for eg i know timing advance (bushes weights) would come before base timing (retarding or advancing)
Things like "use a dwell meter" helps heaps so i know what to research and how to tackle,
Thanks for the wisdom : ) the alternator is already fitted with a resister of which i rewired to recon the connection.

Kghost
Thanks man, i did see mention pertronix fit out, wasnt sure but i am now, should make price research easyier. Seems like a worth while upgrade but am living on a pittance at the moment like most and probably shouldnt have bought a boat lol

RicardoMarine
Thanks for the correction, as i said i found a forum post mention all these things for specifically or 85 merc 3L 470 with a similar story (long storage/back to life)
The circulating pump.
Point gap was just for reference, still not a pro with terminology but i do intend to do everything proper - much differnt to a car lesson learnt!
To be honest i havent research bendix yet, i wrote point notes of everything to easyier manage a plan so cant be sure if i do but thanks in advance, if it is ill loose it and get another.
Im mainly looking for a complete kit so i just have evrything there while im getting deeper into the engine not that she needs an overhaul, i dont think, but i figured do a little extra and regasket some wouldnt hurt plus i do find traces of oil in the engine bay....
I know they are there should have been a comma in there, found a pretty detailed article dividing and discribing both of them : ) understand that much more about combustion engines ha ha
Thank you for everything though, i dont mean to come off argumentitive if i have.
 
Ok so, update.. : (
I was talking to a guy in a parts business over seas and he was having trouble id'ing the motor with me, a few emails back and forth and a photo and he has dubbed it to actural be a merc 470 3.7l
Score on the bigger engine than it was sold as.
But now im having troubles id'ing the starter aswell, can anyone help ? What was stock on these ?

Reason im looking at the starter is i tried to do a compression test and no go.
Starter seems to whind slow and the slower each revolution. I origionally thought this was the battery untill i read a few forums with the same issue saying the starters flogged and voltmeter says a strong 12.1v on the batt.

Compression test came up 1 - 80 2 - 55 3 - 25 lol cant be right considering it held those pressures well
But yeah, think i should start with the starter ? (Shes always been tempermental to start )
Im also thinking just swapping out for replacement/upgrade considering cheap starters ive seen online average the cost of rebuild kits but its all rough figures so any suggestions here ?

The starters massive roughtly 6 inch long 3.5 - 4 inch diameter solonoid is seperate (not housed on )

Also any ideas on where to look for things to id the 470. Sticker on top seems crossbred with information between the 3l and 3.7 and the small badge gave me a serial number to and outboard i belive ( same with the sticker )

This ones a barrel of fun
Thanks for your time, sorry if im to careless about my information

Oh and i had a guy come around and he reckons the detonations from lousy fuel ( 91 octane ) but he didnt touch the motor so it was an educated guess, fingers crossed.
 
Recharge your battery overnight slowly ,it extends the life of your battery. Starter needs to turn faster for a compression test. Measure each cylinder 3 times. Can you turn the engine over by hand with a wrench on the flywheel pulley? There could be mechanical issues within engine, Rings binding ,valves sticking etc. causing starter load
 
Batterys fine its basically new thanks though.
Theres not much room to turn it but i turned it enough and yes it dose grip in the same place every time, i couldnt push it through by handbecause of limited room for levrage but i know its the same place by how it starts.
Is there a way to find out more, further diagnosis that will eliminate what is or isnt at fault.

I have heard of a leak down and if its rings i know not to spend money..
Also heard about putting oil into the cylinders to unseize or prevent seizures, could this be worth while or is it definatly a physical fault.
Engine did sit awhile before now
 
Alright, ive looked for videos and articles cant find anything.
Ive got the valve cover off and not sure what im looking at.., they all seem 'offset' to each other like they were designed to lean slightly towards each other in pairs with the exceptions of the end ones (still a slight lean but not in pair )
Ive never done this sort of work on boat or car so i need some help.
Ive took some photos too ill look into uploading somewhere
 
Am i reading this post wrong, I was under the impression that this engine would turn not over360 degrees, mechnical issues, Anybody?
 
Is there excessive slop in valve lash between the valve guide and one or more of the rockers? That would indicate one of the valves hitting a piston.
 
If you cannot turn the motor over with a wrench pull the distributor cap and turn the crank backwards until the rotor starts to turn make a mark on the damper pulley at the timing pointer and then turn it clockwise until the rotor just begins to turn that tells you how much slop is in the timing chain. It should be less than a few degrees. If it turns over with the plugs out it is likely a hydrolock either coolant or fuel. Does the oil smell like fuel would be a float stuck in the carb and the fuel is washing down the pistons.
 
For starters, sorry guys i stopped getting email notifycations and thought youse had given up on me for being stupid lol thanks for all the replys!
(Stupid as in pic of rockers not valves)

Johnnygr
The motor dose do complete revolutions but at a certain point it will grip and put extra load on the starter.. ive had it started and running but i cant do a compression test because of this. Also thinking this is THE cause of my cascading issue with the boat.

Kimcrwbr1
I will check and get back to you about slop, so im sure what im looking for; i just grab a rocker and push pull wiggle for any untensioned play ? If im right on that i doubt there is cause it all seems pretty tight but safe than sorry : )
Not sure what you mean interference engine? But no it dosnt correct the 'grip area' with the plugs out : (.
Ill do a timming chain check if what i said to johhny hasnt made it issue more clear and is still applicable to do.
 
Interference means if the valves will hit the pistons if cam and crank are out of sync. Does it stick on every revolution? With the plugs out turn the crank with a wrench and see if you can hear where/when it is rubbing. That is a interference engine the pistons have indents for the valves.
 
BTW you do the compression test with all the plugs removed. If you can get the engine to turn over stick your finger in a plug hole and crank on it if you dont feel compression that cylinder is dead. The 470 3.7l is a odd duck probably not the best motor to rebuild for the novice.
 
I dont f****ng belive this,
So i tried to crank it by hand with a breaker bar, still wouldnt budge on the grip point inside seemed like i was starting to strip the bolt ( crap old socket and cant see the bolt )
But not all that much pressure on the bar, considerable but not excessive.
So i tried cranking it by the ignition cause it always manages to crank it past but heres what i cant belive..
The motor has fixed itself ( to some degree )
I now get a continuous revolution without jaring though still loads the starter a bit extra every revolution.
The only things i can think of that would influence this change is
1. When removing the plugs i used a penertrating oil due to seizure and put the plugs in just a couple of threads to keep debree out overnight which allowed a small amount of the lube to get into the cylinder.
2. When i removed the tapper cover i cracked the gasket seal also i only threaded the bolts back in a little over finger tight; seems like they dont really need to be torqued because of clearence and in any case when i was removing the bolts some were only finger tight any way.

Im thinking corrosion/debre in the cylinders ? It still whinds over slowish and i can kind of hear a rubbing sound in amoungst all the moving parts...maybe, i havnt got a helper so im at the front.

I think i mentioned earlier about reading someone putting oil through the cylinders to avoid seizing the engine after long storage, should i do this? I kind of want to, but further questions;
Is there a compound i can put in to eat the corrsion?
How can i get the bulk of the corrosion out without pulling the head ?
If i clean it out best i can before running will little remaining gunk wash through reletivly safly ?
What is the correct method of using fluid/fluids to 'wash out' the cylinders ?

Little bit excited not careless, past day or two i was tossing between fixing this or swapping.

But dont take my word on this you should know more than me about what could be the cause, im just blinding working with common sence rather than knowledge.

Thanks for your help to kim, much appreciated : )
 
Back
Top