Replacement engine from Rapidomarine...

[John_S]

Re: Replacement engine from Rapidomarine...

Since the knocking stoped, you need to keep running the high octane mixture.

Are you near full advance (20-22 degrees) at 2700 rpm?

You do need to check those plugs. Make sure there are not metal deposits on them. I'd leave the iridiums out until you get it fixed. They will probably be harder to read for lean/rich condition, as well.

Vacuum of 14" at idle would be low for my 350 V8 at about 1000' elevation. 17/18 and steady is normal for mine. I don't know about a 4.3L and your elevation. It should be very steady and not wandering. What is the vacuum at 2700 rpms?

A few links on vacuum readings:

http://www.secondchancegarage.com/public/186.cfm

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm

http://www.international-auto.com/f...uges/tips-on-reading-gauges-vacuum-gauges.cfm

As far as the cam, what does the builder say is suppose to be in there? I remember posts about Rapido installing some performance cams in V8s that had suspicious specs for a marine engine.

BTW, what carb do you have? I am sure you already posted it, but didn't want to search the 3 pages of this thread.

 

[FreeBeeTony]

Re: Replacement engine from Rapidomarine...

3 questions:

1) are we sure the tach is accurate?

2) are we sure all 6 cylinders are firing?

3) what is your speed at 2700RPM's?

just a couple of ideas........

 

[kwoolard]

Re: Replacement engine from Rapidomarine...

You say you're advance "seems" to be working fine. You really need to verify as if it isn't advancing past the base timing, you will get a major power loss.

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

3 questions:

1) are we sure the tach is accurate? New tach on timing light, almost identical to tach in dash

2) are we sure all 6 cylinders are firing? I am positive there is no miss.

3) what is your speed at 2700RPM's? The speedometer on the dash is inoperable, I have a hand held GPS that I could get the speed with if that were necessary..

just a couple of ideas........

Thanks for the thought provoking questions, gets us all on the same page..
still thinking,
Kevo

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

You say you're advance "seems" to be working fine. You really need to verify as if it isn't advancing past the base timing, you will get a major power loss.

I know the advance is working, exactly how much advance is uncertain, I know it is at least 22degrees @ full advance, it may be 30. I have adjusted the timing so many times its all a blur at the moment. I will note exact advance values next time I set it up. Currently set @ 8degrees BTDC @ 700rpm
still thinking,
Kevo

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

Since the knocking stoped, you need to keep running the high octane mixture.

Are you near full advance (20-22 degrees) at 2700 rpm?

You do need to check those plugs. Make sure there are not metal deposits on them. I'd leave the iridiums out until you get it fixed. They will probably be harder to read for lean/rich condition, as well.

Vacuum of 14" at idle would be low for my 350 V8 at about 1000' elevation. 17/18 and steady is normal for mine. I don't know about a 4.3L and your elevation. It should be very steady and not wandering. What is the vacuum at 2700 rpms?

A few links on vacuum readings:

http://www.secondchancegarage.com/public/186.cfm

http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm

http://www.international-auto.com/f...uges/tips-on-reading-gauges-vacuum-gauges.cfm

As far as the cam, what does the builder say is suppose to be in there? I remember posts about Rapido installing some performance cams in V8s that had suspicious specs for a marine engine.

BTW, what carb do you have? I am sure you already posted it, but didn't want to search the 3 pages of this thread.

The carb is the stock Rochester Quadrajet that came on the boat. I rebuilt it with new gaskets, cleaned all the jets and installed new needle/seat, pristine clean. I know from motorcycle restorations that clean is the word...
I do not know what the vacuum is @2700rpm, I will soon though on muffs and on the water.
I emailed the builder this a.m. and asked about the cam specs, I am prepared to profile the one currently in the engine and compare to the cam from the frozen engine, I am prepared to swap them if I find something different since the old cam made good hp despite the fact the cooling system was spewing everywhere. All bolt on items, i.e. carb, ignition items, charging system, cooling bolt ons, were fine prior to new long block. I have good compression, good spark, no misses, good idle, good oil pressure, all four venturi's of the carb have fuel flowing during WOT but still wont break 2700rpm on the water. It is either the cam or the ignition advancing too much which I am doubting it to be, I can retard the advance to 22degrees full advance while on the water and see if it is that, I doubt that will be it, I am suspecting the cam at the moment, thoughts?
cheers,
Kevo

btw, I plan to read the links provided, thanks for the help, it may turn up something, I have to process as I can...just too old for this...hahaha..

 

[scipper77]

Re: Replacement engine from Rapidomarine...

According to what i have read the only thing we seem sure is wrong is the high compression. (not sure how that helps)

just things to throw out there (not what I think is the problem)

Fuel pump is supplying enough gas under load and at rpm/filter restriction?

Electronic ignition issues?

Restriction in the exhaust/back pressure issues?

Poor grounding somewhere in the electrical system?

I'm not much of a mechanic so I don't know if any of this helps but I figured it couldn't hurt.

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

According to what i have read the only thing we seem sure is wrong is the high compression. (not sure how that helps)

just things to throw out there (not what I think is the problem)

Fuel pump is supplying enough gas under load and at rpm/filter restriction?

Electronic ignition issues?

Restriction in the exhaust/back pressure issues?

Poor grounding somewhere in the electrical system?

I'm not much of a mechanic so I don't know if any of this helps but I figured it couldn't hurt.

Any and all input GREATLY APPRECIATED! I just read the 3 links concerning the vacuum gauges uses and how to read them and have already come to some conclusions....I suspect an unusual cam and will find out if it is even if the builder doesnt help and I will check for exhaust restrictions which I dont think I have but, hey, I am human, I could have dropped a box of cigars down one of the exhausts, who knows, lol. I am going to make new grounds for everything concerning the ignition system(adding grounds).
Again, thanks for all suggestions.
cheers,
Kevo

 

[coheej]

Re: Replacement engine from Rapidomarine...

The builder told me the block is .30 over(<which raises compression) with flat top pistons to lower the compression as opposed to dome topped pistons. He builds and sells a lot of engines...I asked him about the high compression and he was thrilled he built one with it, I was hesitant about it too, but I am sure it won't last....I can smell the valves leaking while I type....lol...
Kevo

The .030" overbore would only increase the compression by about a tenth of a point.
It's strange the builder doesn't know the cr of the engine he's supplying.
Did you ask for it to require 93 octane?

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

The .030" overbore would only increase the compression by about a tenth of a point.
It's strange the builder doesn't know the cr of the engine he's supplying.
Did you ask for it to require 93 octane?

All I asked of the builder was to "try and send a good one".....

 

[redjmp]

Re: Replacement engine from Rapidomarine...

You need to install regular plugs and run for a while under load and then pull and read them. I really think if you have good spark and fuel that the problem is with the block especially since it has too high compression. Normal marine engines should be able to run on regular 87 octane gas not 93!!! For that reason alone I would call Raul at rapido and ask him to send one with a normal compression ratio that can run on 87. Wrong cam, wrong cam timing, wrong pistons, wrong heads or ones that were planed are probably the culprit. In any case if your new plugs look fine after your next trip, then I wouldn't waste any more time with it. Get a replacement.

 

[PBarrett]

Re: Replacement engine from Rapidomarine...

I'm a little late to this discussion, but to me it sounds like it's a cam timing issue. If the cam is too far advanced it will raise the cylinder compression, and will knock quite a bit of power out of the engine. If you are not familiar, or comfortable, with degreeing a camshaft, I'd contact the builder and get a replacement.

It's entirely possible that Rapido may have received a mis-matched, or incorrectly drilled, timing gear set and that is what is causing your problem. I doubt that any rebuilder actually checks cam timing because they are not building a high performance engine.

PB

 

[Flukinicehole]

Re: Replacement engine from Rapidomarine...

I know this may sound stupid but are you sure your throttle plates are opening all the way? I always start with the easiest answer and have seen this before. If this is a repeat question I'm sorry. If they are opening all the way then I would suspect cam timing also.

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

I know this may sound stupid but are you sure your throttle plates are opening all the way? I always start with the easiest answer and have seen this before. If this is a repeat question I'm sorry. If they are opening all the way then I would suspect cam timing also.

Throttle plates, yes, visible while on water with my own eyes....cam timing remains to be seen, waiting on reply from Raul as to what cam and specs....I have to problem with degreeing a cam, just dont want to...
Any and all questions, remarks and thoughts are welcome, you cannot belittle me any more than I have been by this project, I am so humble I could walk under the edge of a mushroom....
Gearing up for a cam of a good time in the coming weeks, I just may swap it out for the old one and get it over with....
cheers,
Kevo

 

[mikeneal]

Re: Replacement engine from Rapidomarine...

I agree with the guy who said cam timing is off, maybe a tooth or something was mis-machined.

 

[redjmp]

Re: Replacement engine from Rapidomarine...

At 2700 is your boat out of the hole or are you pushing a lot of water? Maybe just not quite enough torque to get it over the hump and planing well at which point the hp not torque will get you going faster..

If you think all the systems are ok, then get a buddy to drive at wot while you turn the distributor by hand. Keep advancing until it knocks and then pull it back until it doesn't.
I have read that you can go a little past 30 degrees total timing depending on your setup.


I'm assuming it trailered and has no issues with things growing on the bottom...

There's no issues with the drive or prop? Btw what kind of prop is it? Nothing has been changed has it? Boat didn't get heavier?(waterlogged)
Same drive?(drive ratio)

Beyond that, you would have ruled everything else out?

Did you say you installed the cam?

For peace of mind, I would check your compression gauge on another motor or better yet against another gauge to see if indeed you have 210psi.

What about your old motor? Was it a vortec?

Don't think they came stock but it may have been upgraded?

Dont think the intakes swap over so unlikely but...

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

At 2700 is your boat out of the hole or are you pushing a lot of water? Maybe just not quite enough torque to get it over the hump and planing well at which point the hp not torque will get you going faster
..............@2700 still not planed out, pushing water....almost out though....

If you think all the systems are ok, then get a buddy to drive at wot while you turn the distributor by hand. Keep advancing until it knocks and then pull it back until it doesn't.
I have read that you can go a little past 30 degrees total timing depending on your setup

................just did that Monday or Tuesday afternoon, cant remem the day, everything you just said....ended back @8deg BTDC


I'm assuming it trailered and has no issues with things growing on the bottom.

.................bottom is clean and the paint is new, well first time it got wet was 2 months ago and inside the hull is dry as a bone....

There's no issues with the drive or prop? Btw what kind of prop is it? Nothing has been changed has it? Boat didn't get heavier?(waterlogged)
Same drive?(drive ratio)..

..................same everything, just swapped out new reman for old frozen engine.....old engine ran fine, just was spraying frothy oil/water everywhere....

Beyond that, you would have ruled everything else out?

.........................My old, tired, broken down brain has almost stopped ruling things out, but here I go, about to swap a cam, lol..

Did you say you installed the cam?.

......................no, the vendor did, he reman the longblock...

For peace of mind, I would check your compression gauge on another motor or better yet against another gauge to see if indeed you have 210psi.

.........................I have 2 gauges, I was just happy as a lark to have that much when tested, the gauge I used is like new, but, I will use my old one to check for accuracy...

What about your old motor? Was it a vortec?

.......................both are NON vortec, everything bolts up like before...

Don't think they came stock but it may have been upgraded?

........................... Vortec heads and manifolds are differant as well as the valve covers...

Dont think the intakes swap over so unlikely but...

..........................I am going to call the vendor and ask him about the cam, if he is no help, I will check the lift of my known good cam and probably swap it, I just dont want to, I am sick of troubleshooting....a crippled/choking on chronic pain/tired of working on my sons boat for free/over the hill/jack of all trades/garage full of tools/shoulda got a block and bored it myself/taking pain meds all day/HATE THIS BOAT and IT ISNT EVEN MINE!

..................there, I feel better, well, not really, but its time to try and get some sleep and that just kinda slipped out, I am sure some of you feel the same way or close at times...
As I said earlier, I appreciate each and every suggestion that comes my way because within all of them lies the root of this engines problem and the process of elimination is what troubleshooting consists of...

many thanks,
Kevo, headed to the rack to wrestle the sheets till daylight!

and, I am going to look at an old motorhome on Saturday, I need another endless money pit of a project, lmao!

 

[John_S]

Re: Replacement engine from Rapidomarine...

I know the advance is working, exactly how much advance is uncertain, I know it is at least 22degrees @ full advance, it may be 30. I have adjusted the timing so many times its all a blur at the moment. I will note exact advance values next time I set it up. Currently set @ 8degrees BTDC @ 700rpm
still thinking,
Kevo

Please report back on that. Also what ign module. It should be V6-14, and your total should be 22 (with 8 initial). According to the timing curve you should have full advance by 2700. If you have 30, thats way too much, contributing to why the higher octane ran better and maybe part of performance problem.


Check the advance, then the cam.

IMHO, measure cams before swapping. Just swapping will/can lead to more fustration.

 

[nightowl]

Re: Replacement engine from Rapidomarine...

...After reading thru the problems your having it made me think of a thread i read about having low power and get up to correct rpm/speed it finally ended up being that his engine coupler was shot, are you using the same engine coupler from your old engine?......I attached the thread even if its not that there were some good trouble shooting ideas in it.

http://www.sterndrive.com/board/show_subtopic.cfm?ID=4294&TopicID=43

Good luck!

 

[choochooharley]

Re: Replacement engine from Rapidomarine...

Did you say that you can get past 2700 on the muffs just not in the water? If so I would check the coupler or maybe with a new engine with the higher compression and such you need a different prop. Maybe a lower pitch prop to raise the rpms? Just throwing some ideas out there