Replacement engine from Rapidomarine...

[Kevoz]

Re: Replacement engine from Rapidomarine...

After everything I have tried/checked/troubleshot, I have concluded that this block is incapable of making enough hp @ 2800rpm to get this boat out of the water. I am no longer in a hurry to get it right and will now get a leakdown tester cobbled together and see if the cylinders are holding enough pressure. It seems that everything I try has the same effect and it still boils down to one common component, the long block purchase has to be proven worthy and this shall tell the tale....I hate winter here and this mind eating problem will just make it worse, aack! Wish me luck at finding the smoking gun!

cheers,
Kevo

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

Regardless of what you think a 4.3L can take in advance timing comparing it to the 350, the reality is he is running the stock advance, as he should. In the other thread where you thought that this was the issue, it turned out to be the wrong spark plugs. http://forums.iboats.com/showthread.php?t=446204 The marine 4.3L is fine with only 22 degrees of total advance.

I just don't buy it..been doing this too long. Even aircraft engines with dual ignition (2 flame fronts) run more than 22 total. NOTHING with a 4" bore will produce proper power at that total advance.Throw in that a 4.3 is IDENTICAL to a 350, and it becomes more relevant. 22 degrees in the MODULE, 8 or 10 degrees initial, THAT I'll buy. That would be the same as a V822 or V822A module..all in at 3500 to 4500 rpms. With vortec (high turbulence) heads, thats perfect.

It's all about TIME..how long it takes for the flame front to spread across the cylinder and build maximum pressure AT THE CORRECT TIME.

Of course, if it is indeed 22 degrees TOTAL, that would explain the apparent low idle vacuum. I get about that in my small block Fords, but jumps right up to over 20" at about 1000 rpms. Ford cam is supposedly 206 /221 @ 114.5 lobe centers. Flat tappet.

 

[John_S]

Re: Replacement engine from Rapidomarine...

I just don't buy it..been doing this too long. Even aircraft engines with dual ignition (2 flame fronts) run more than 22 total. NOTHING with a 4" bore will produce proper power at that total advance.Throw in that a 4.3 is IDENTICAL to a 350, and it becomes more relevant. 22 degrees in the MODULE, 8 or 10 degrees initial, THAT I'll buy. That would be the same as a V822 or V822A module..all in at 3500 to 4500 rpms. With vortec (high turbulence) heads, thats perfect.

It's all about TIME..how long it takes for the flame front to spread across the cylinder and build maximum pressure AT THE CORRECT TIME.

This guy is pulling his hair out trying to figure out what is going on with his STOCK replacement engine. Please start another thread and we can continue to speculate on why 4.3L advance timing is ony 22 total, etc. Maybe just copy and paste into a new thread.

Of course, if it is indeed 22 degrees TOTAL, that would explain the apparent low idle vacuum.

How is that? They both have only 8 degrees initial and that is what it would be running at idle. Total advance has no impact at idle.

I get about that in my small block Fords, but jumps right up to over 20" at about 1000 rpms. Ford cam is supposedly 206 /221 @ 114.5 lobe centers. Flat tappet.

I have no idea what your small block fords are set up to, but 14" is considered low for "general" normally asperated engines (see the vacuum links I posted). What elevation are you at? Add 1" to your readings for every 1000'.

You need the cam timing info, intake lobe centerline to TDC number, ie what the cam is degreed to. Then you can calculate at what point the intake valve is closing during the start of the compression stroke.

 

[fat fanny]

Re: Replacement engine from Rapidomarine...

Kevos maybe you need another set of eyes preferably qualified to help out or look @ it while running you just maybe missing something it happens to us all. I just hate to see you go through all this with winter @our doorstep with no solution after all you need the underload test to prove it out and get a fix and or solution!!!!! as always Good luck!!!!!!!!!

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

We'll assume the SPOUT wire was disconnected/grounded when setting initial timing. 8 degrees initial + 22 degrees in the module is a perfect starting point.

Is the damper/TDC mark accurate?

Is the tach accurate?

The quadrajet air valve opens on airflow only. Early opening causes lousy fuel atomization, but the engine should eventually spool up.

If the cam is off a tooth, retarded, it won't have any bottom end. Would cause loss of low end power, and low vacuum.

Low compression from rings would result in massive blowby, and would blow oil out of every opening in the engine.

If the timing is correct, and the carb is anywhere near acceptable (worked on the other engine?) then it has to be a mechanical problem. Sounds like the cam chain is off a tooth.

Can't be internal friction. Engine oil would be hotter'n hell.

 

[GLENN M]

Re: Replacement engine from Rapidomarine...

the one thing you changed,rockers not sure if you changed push rods.i would change back and try,did you check rocker arm geometry,when you change rockers to roller rockers you have to check geometry. you cant assume from one engine to the next it will be the same.block decked ,head milled, valve grind, valve stem height,all effect geometry.first step put it back the way it came.or get out dial indicater and start measuring.at 50 percent lift you want rocker contact in middle of valve tip.did you adjust valves with motor running,lossen till they clack tighten till they just stop then half to three quarter turn,i think you have valve train issues

 

[GLENN M]

Re: Replacement engine from Rapidomarine...

ps if valves to tight or to long push rod when you rev engine lifters will pump up and valves wont close,causing lack of power and no rpm,replace to stock or find out how to check geometry

 

[redjmp]

Re: Replacement engine from Rapidomarine...

V6 motors fire every 120 degrees while V8's fire every 90.
Hmm lets see.. 30/90's more rotation = 33% more rotation between energy pulses.
When you fire BTC, the engine needs to over come this anti-rotational force... If you advance too much, you lose power. The amount increases exponentionaly with more advance ~the difference between 29 and 30 degrees having a much greater effect than the difference between say 9 and 10. This is because of the lever action of the crankshaft as it rotates. 90 degrees after TDC is where the power is converted most efficiently into rotation as this is where the crank has the biggest leverage.
With a V8 you can get away with more timing because the next power stroke happens much sooner and helps the engine overcome the anti-rotational energy.
So that is why even though the bore and stroke is the same, the V6 cant take as much timing as a V8.

As was evidenced by the OP's tweaking the timing under load only to find out it was only able to take about 22 degrees before knocking or losing power.

Obviously, now that all the other possibilities have been exhausted, the only thing left is the engine itself.

I'm sure tearing into it will reveal the cause of the problem but doing so would void the warranty.

As I have said all along, send it back!

You don't want a high compression engine for anything but a racecar.

Where can you find 94 octane on the water anyways? Here where I live 92 if you can find it is about a buck a gallon more!

The real problem though is not the abnormally high compression on its own as it should work with 94 gas and make power, the problem is WHY it is making these numbers if it was built to marine spec!
Probably something as simple as being off one tooth on the cam but then again making it breath worse shouldn't bump up the psi.
Imho, this is a mismatch of pistons and heads along with a wrong or improperly installed cam.. Could also be that the block was decked and/or the heads shaved but the engine should make power if that was the only variable...

Sadly though, I don't think we will ever find out because as I have said before, tearing into it will no doubt void the warranty...

 

[CharlieB]

Re: Replacement engine from Rapidomarine...

Poor spark at high rpm's: cracked coil, bad wires. Get a spark tester was the solution for diagnosing. "An inline spark tester is an inexpensive tool and it will let you check the spark while the engine is bogging."

scipper tried to get you headed in the right direction.

Spark QUALITY at RPM can, and will, limit RPM, ESPECIALLY on a motor with raised compression.

The additional compression increases air resistance to spark, effectively increasing the voltage necessary to bridge the same gap as the previous engine.

An old street racers trick was to reduce the spark plug gap to test and see if you gained any more power/RPM.

In reality, you want a large gap HOT spark to provide a good flame ignition.

This requires substantial voltage.

Test spark in free air using an adjustable gap tester set to 1/2 inch minimum, you should see a bright blue SNAP, any less will limit RPM under full load.

The OEM coil may be inadequate for your newfound compression.

 

[squeak911]

Re: Replacement engine from Rapidomarine...

Have you checked the resistance of all the plug wires? I had a one plug wire that was bad causing my 4.3 engine to not get to full RPM.

 

[choochooharley]

Re: Replacement engine from Rapidomarine...

Have you pulled the plugs and tested the spark too see if its a weak spark

 

[scipper77]

Re: Replacement engine from Rapidomarine...

scipper tried to get you headed in the right direction.

Lets look at this from the basic engines for dummies level.

You need.....
Fuel (check)
Air (Check)
Spark (no check yet)
Compression (check, it's high)
timing (check with the exception of the possibility of wrong cam)

Did I miss anything?? (I'm not nearly the mechanic that most of you are so that is a serious question)

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

V6 motors fire every 120 degrees while V8's fire every 90.
Hmm lets see.. 30/90's more rotation = 33% more rotation between energy pulses.
When you fire BTC, the engine needs to over come this anti-rotational force... If you advance too much, you lose power. The amount increases exponentionaly with more advance ~the difference between 29 and 30 degrees having a much greater effect than the difference between say 9 and 10. This is because of the lever action of the crankshaft as it rotates. 90 degrees after TDC is where the power is converted most efficiently into rotation as this is where the crank has the biggest leverage.
With a V8 you can get away with more timing because the next power stroke happens much sooner and helps the engine overcome the anti-rotational energy.
So that is why even though the bore and stroke is the same, the V6 cant take as much timing as a V8.

What? The configuration has nothing to do with it. Peak pressure is achieved at TDC, or slightly after. At 90 degrees, there's very little pressure left.

 

[redjmp]

Re: Replacement engine from Rapidomarine...

What? The configuration has nothing to do with it. Peak pressure is achieved at TDC, or slightly after. At 90 degrees, there's very little pressure left.

Wrong again Aloysius. Peak cylinder pressure (PCP) occurs ( or should occur ) at very close to 16 degs ATDC.
At TDC even though the combustion pressure is rising, the engine produces zero power. It has no mechanical advantage whatsoever.
It produces the most power, Maximum Brake Torque (MBT) at very close to the PCP .
So an engine goes from making zero power to making maximum torque in a span of only 16 degs!

http://www.sdsefi.com/techcomb.htm
http://www.gonefcon.com/whatifdyno/combustion.htm

You certainly can give the v6 more timing but you are asking for trouble if you try to run v8 timing specs on a marine v6 engine.
Unless you know something that the Mercruiser and Volvo engineers didn't understand.
Keep in mind that this mighty V6 is the most fuel efficient and produces the most power per cubic inch than any other inboard offered by either company. In other words, it running close to the ragged edge already.
All the while running 22degs total advance.
Go figure!
I can see them leaving 2 or 3 degs on the table for a safety margin but no way would they leave 12!
The other company would surely claim that extra power wouldn't they?

 

[redjmp]

Re: Replacement engine from Rapidomarine...

What? The configuration has nothing to do with it. Peak pressure is achieved at TDC, or slightly after. At 90 degrees, there's very little pressure left.

Wrong again Aloysius. Peak cylinder pressure (PCP) occurs ( or should occur ) at very close to 16 degs ATDC.
At TDC even though the combustion pressure is rising, the engine produces zero power. It has no mechanical advantage whatsoever.
It produces the most power, Maximum Brake Torque (MBT) at very close to 20 degs ATDC. This is a direct function of the PCP and crank angle.
So an engine goes from making zero power to making maximum torque in a span of only 20 degs!

http://www.sdsefi.com/techcomb.html

You certainly can give the v6 more timing but you are asking for trouble if you try to run v8 timing specs on a marine v6 engine.
Unless you know something that the Mercruiser and Volvo engineers didn't understand.
Keep in mind that this mighty V6 is the most fuel efficient and produces the most power per cubic inch than any other inboard offered by either company.
All the while running 22degs total advance.
Go figure!
I can see them leaving 2 or 3 degs on the table for a safety margin but no way would they leave 12!
The other company would surely claim that extra power wouldn't they?

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

Red, you're clueless. Quit reading baloney. There's not much argument about pressure vs. angle of rotation, but the number of cylinders is totally irrelevant. Frankly, rod length has an important affect on power vs. degrees of rotation. Often, we rotate the pistons to take advantage of the pin offset for this very reason.

At 90 degrees, the exhaust valve on many engines is thinking about opening.

 

[StevNimrod]

Re: Replacement engine from Rapidomarine...

Lets look at this from the basic engines for dummies level.

You need.....
Fuel (check)
Air (Check)
Spark (no check yet)
Compression (check, it's high)
timing (check with the exception of the possibility of wrong cam)

+1. Back up a few and look at birdseye at: spark, timing, and compression.

Compression is high, but why? Need more info to compute static compression ratio. Depending on the variables, you might be in the range of 9.5-9.7 to 1; maybe higher. Does this jive with your measured compression figures? Do you want to always run premium? Just things to consider; an extra couple hundred a year in premium fuel might play in the decision to pull the engine in favor of something you can run on regular.

Just a shot in the dark, but my 383 is 8.5:1 and I got a 200+ compression reading on one cylinder once...due to water being on top of the piston (in my case a cracked block). Maybe pull plugs and crank over just to eliminate water being where it shouldn't?

Timing seems confirmed to factory specs, including advance. Cam timing is still on the table, but maybe after some more easy stuff is looked at.

Spark is where I'd be interested in looking. More specifically, the resistances of spark plug wires, the coil lead wire, and the primary and secondary resistance of the coil itself. My coil/lead went at the end of this season and symptoms were similar to what you described. If your coil isn't stock, you should be able to call the manufacturer and get specs and tolerance. For me I had to be within 10% of spec. At 10.1% out of spec the coil was considered bad.

I'm wondering about the fuel pressure too. I run an electric pump and I'm 7psi idle (for sure), but I don't think I drop below 5psi at WOT.

I know it's frustrating to be in this situation. Got the t-shirt. But in the end it normally goes down one of two ways: 1) you find the problem, or 2) you run out of things to troubleshoot. It's as simple and as complicated as that.

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

Here are the things I am still considering:

The fuel pressure @ WOT on the water fluctuated from 2-4psi, even though the rear AV was not opening all the way, when I did open it it made no difference, when I closed it it made no difference, so, it still may not have been getting the fuel that it needed, I will replace it.
The ignition system, I feel that the plug wires are fine, not all wires will go bad at the same time, it has never misfired, they are Accel wires and I am not losing random sparks in the dark. The ignition coil is also an Accel Super Coil, I can replace it easily too, but I am not convinced that this is the problem. I will replace it when/if necessary.
Engine/cam/cylinders, I have built a dual gauge/leak down tester and acquired a piston stop and some degree tape for the harmonic balancer. If the cylinders check out to be good, will proceed to above troubleshooting.

I am currently on the backside of being sick with my seasonal alergies/asthma and hope to get to these checks before I have to cover it for the winter as the engine not going past aforementioned rpm's is a slow eating cancer for a seasoned mechanic. I shan't give up, I want to see just how good this engine can run and besides, I'm not a quitter, if I were, I would not be spending time with like minded individuals and friends as all of you are. Thanks for all the effin help and to be the first to say it, Happy Holidays!
cheers,
Your friend, Kevo

 

[LAC_STS]

Re: Replacement engine from Rapidomarine...

You have points?

I had a brand new engine that wouldnt go over 3K RPM and the problem ended up being the resistor wire going to the coil.



If you run a 12V wire from the batt to the coil then see if it will run higher RPMs you will know if its the resistor/resistor wire.

Ballast resistors are only about $10.

 

[StevNimrod]

Re: Replacement engine from Rapidomarine...

The ignition system, I feel that the plug wires are fine, not all wires will go bad at the same time, it has never misfired, they are Accel wires and I am not losing random sparks in the dark. The ignition coil is also an Accel Super Coil, I can replace it easily too, but I am not convinced that this is the problem. I will replace it when/if necessary.

Kevo,

It might be easier to check the ignition system, especially if that is the actual problem. I say that because I also have Accel wires and an Accel Super Coil. My coil is part number 140008 (previous owner ran one and I didn't know any better when I replaced it when I had my engine out). On the off chance yours is the same, the spec'd primary and secondary resistances are 0.500 ohms and 9.6K ohms, respectively. According to talking to Accel, I should be within 10% of these specs, or (0.45 - 0.55 ohms primary, and 8.64 - 10.56 ohms secondary). I wasn't in this range. While I had the meter out I checked the coil lead wire and it too was out of spec. It was before the last trip of the season and all I had was a spare coil lead wire; replacing it and I had full power again. I didn't have any lost sparks or other things that would point to the coil/wires, just got lucky. Anyway, I asked Accel about this (since they are local - Cleveland, OH) and the tech I spoke to said they really recommend their Mallory line of coils for marine use - they come with a 2 year warranty and apparently better hold up to vibration, which apparently killed my Accel coil in two seasons.

Just wanted to share notes; hopefully it's helpful.

Happy holidays to you and yours as well!