Significant but strange engine problems. 5.7L Mercruiser MPI Horizon.

alldodge

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I don't know a 4K boat with full load of water and gear and can get to about 2900 rpm. The 190 psi for cylinders is a bit high unless it has been bored out, the 150 range is more inline. Your timing is still not right, it needs to be set correctly
 

davus

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hi alldodge. Sorry about the delay in reply. Its a busy time of year!.

Tomorrow im going to take the boat out on the water (30 degrees celcius and 2 knots winds!). I plan to do a few baseline test runs to record maximum RPM on takeoff and on cruising.

You comment that my timing is not set correctly, which id like to clarify and get right before tomorrow.

The way i set the timing was to put the engine into base timing mode (paperclip on points A and B of the DLC) and then adjusting timing.

Only problem i have is that i cant actually tell where 8 degrees is????. My engine only has one timing mark on the timing cover, and one timing mark on the balancer.

Below is a youtube video of my timing marks.

https://www.youtube.com/watch?v=6taMfWtgOvo

How do i know where to set the timing??.

Many thanks

Dave
 

alldodge

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Looks like you have 3 choices, a Merc scan tool, an advance timing light, or timing tape.

With an advance timing light, the timing your looking for an be adjusted on the light and then you just align the two marks together on the balancer and cover.

Can get some timing tape from a local or online auto parts store. Measure the diameter of your balancer, and then apply the tape to the balancer
http://www.summitracing.com/parts/msd-8985?seid=srese1&gclid=CK_g6uag7skCFUsbgQodmF4MGQ
 

davus

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thanks AllDodge.

I also posted this question on another boating forum, and the answer i got was that the mark you can see in the youtube video IS the 8 degree timing mark.

Can you confirm / deny this?

Many thanks

Dave
 

alldodge

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IS the 8 degree timing mark.

Never heard of that before, :pound: it is a pretty good story. Who ever said that would have to prove it before I would believe it. Then the next question I would ask is, how do you set up the timing when building the engine?


Edit: have you tried taking some sand paper to the balancer area to see if the marks are covered by paint?
 
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davus

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alldodge, im with you. Thus the exact reason i was looking for confirmation.

If there is no TDC mark on the balancer - setting TDC when buiulding the engine could prove difficult.

The only way i can think of to confirm where tdc is is to either pull a rocker cover and inspect valve location, and/or pull #1 spark plug and check for location when alledged TDC mark is lined up.

However we're only talking about 8 degrees. And im not sure those visual references will be definitive enough.

I really need a mercruiser expect.

Havent had a go at cleaning the balancer yet - will do that now.

Dave
 

tpenfield

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Without the individual marks of before and after TDC, my assumption would be that the single mark is the timing point (8 degrees before TDC). IT would be tough to physically verify it though, but if you can get a glimpse inside #1 cylinder you might be able to tell if the mark is before the piston tops out.
 

davus

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Hi Guys,

So this morning we popped down to the bay and went for a squirt. Perfect morning for it. barely a breath of wind.

I did 6 runs with the 20P props, and then 6 runs with the 22P props.

Each run with the 20P props were within a poofteenth of each other.
TakeOff WOT = 2950 RPM
Cruising WOT (with boat trimmed up) = 5000 RPM
Top Speed was about 50 knots give or take.

Likewise each run with the 22P props were almost identical.
TakeOff WOT = 2750
Cruising WOT - 4900
Top Speed was about 55 knots give or take

No pinging at all, and great throttle response once up.

Top end seems fine, and im certainly reaching the 5000 RPM mark. I just seem to be lacking a few RPM's on takeoff.

Youtube video of boat taking off and WOT.

https://www.youtube.com/watch?v=wuJVcmjo3JE

What are your thoughts?

Dave
 

tpenfield

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Yes, seems fine.

So, summarizing what finally was the cure?
 

alldodge

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Yes, what did you change?

Top end seems fine, and im certainly reaching the 5000 RPM mark

Starting to think your tach is off. Your WOT should be no more then 4800 and would figure your rev limiter is about 4950 give/take
 

davus

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Hi Guys,

Firstly just to confirm the speeds i posted above, these are clearly incorrect. I'm not sure why the speedo on the boat is so far out, but ill need to look into this. I confirmed this morning with a GPS speedo app on my iphone, that the speeds are infact much lower than this (not an issue to me at all, but just wanted to clarify).

My max theoretical speed using 22" props and at 4900 RPM, and a 2.00 ratio on the outdrive is as follows.

5000 X 20" / (2*3.2808*200*1.852) = 44.35 knots. Allowing 5% slippage i get 42.14 knots. And because im a downunder Aussie ......... 78 km/h. Which is right on the money. The speedo GPS app on my phone showed 77 km/h.

However the main point is im hitting my 5000 RPM, and i seem to be getting out of the hole without too many issues (albeit the real test will be with gear on board, my family, and a guest family - which i usually when i have issues.

I think the main problem was the distributor cap to be honest. Certainly when i changed this, my pinging disappeared straight away, which allowed me to focus on timing. I have set the timing to a fairly conservative 7 degrees. I think i will give it an extra 2 degrees and see how it goes.

I also redid the wiring to my coil. Not sure that this would have helped with top end / bottom end. But i think this fixed the issue i had with surging (as soon as i touched the coil sire with my hand - it fell off completely)

I now need to start another thread as i think im having issues with my charging system!. Its a never ending story! LOL

Dave
 
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