Mr_Asa
PowerDork
7/29/21 12:45 p.m.
Curtis73 (Forum Supporter) said:
On the amperage/compression... I think you're getting an X-ray when you need an MRI. By that I mean - real compression test. I would imagine that something as simple as a different resistance plug wire or smaller plug gap could send those amperage spikes in any direction.
We are talking about 50kV in carbon-trace ignition wires with an intentional gap in the circuit that it has to cross.
The nice thing is, it's a 350 with no special internal parts. It's a bone-stock GM goodwrench longblock off the Chevy assembly line that Mercruiser finishes assembling. If there is something that is out of whack and isn't fixed by just running the cobwebs out, it shouldn't be hard to fix. Its rare that a stuck ring can't be fixed with a little kerosene or diesel or kroil. A valve will mean pulling a head. Partially collapsed lifters aren't out of the ordinary, but it's a roller cam motor so you could swap out one pair of lifters.
Anything bigger than that (hole in a piston, scored cylinder bores, etc) would likely show up as a misfire or a noise.
I think you misread it. Ammeter is on the starter, ignition is disabled. Amps spike when compression puts a resistance on the starter. Kind of a great idea provided you have enough history to analyze it properly.
ultraclyde said:
Interesting. In looking at parts I've seen Mercruiser 5.7 EFIs offered in Reverse rotation so I thought it was still a thing. Maybe they were for repowering older craft.
That is possible, and also potentially foreign markets. A 26' boat I was on before the pandemic in Costa Rica had a reverse engine and I don't think it was that old... maybe early 80s, late 70s?
They're not gone, just dramatically reduced since the advent of the Alpha MR.
Mr_Asa said:
Curtis73 (Forum Supporter) said:
On the amperage/compression... I think you're getting an X-ray when you need an MRI. By that I mean - real compression test. I would imagine that something as simple as a different resistance plug wire or smaller plug gap could send those amperage spikes in any direction.
We are talking about 50kV in carbon-trace ignition wires with an intentional gap in the circuit that it has to cross.
The nice thing is, it's a 350 with no special internal parts. It's a bone-stock GM goodwrench longblock off the Chevy assembly line that Mercruiser finishes assembling. If there is something that is out of whack and isn't fixed by just running the cobwebs out, it shouldn't be hard to fix. Its rare that a stuck ring can't be fixed with a little kerosene or diesel or kroil. A valve will mean pulling a head. Partially collapsed lifters aren't out of the ordinary, but it's a roller cam motor so you could swap out one pair of lifters.
Anything bigger than that (hole in a piston, scored cylinder bores, etc) would likely show up as a misfire or a noise.
I think you misread it. Ammeter is on the starter, ignition is disabled. Amps spike when compression puts a resistance on the starter. Kind of a great idea provided you have enough history to analyze it properly.
I did misread. apologies.
The seller is on vacation and the boat is in the shop for diagnosis. Hoped to hear something by now but not surprised. He'll be back in town Wednesday I think.
Waiting on a verdict is killing me.
GeddesB
New Reader
8/1/21 9:51 a.m.
Wednesday?! This thing could have been LS swapped by then.....
Speaking of LS swaps, here's one resource I found for all you LSSWAPALLTHETHINGS!!!11!! guys:
https://www.cpperformance.com/c-2078-ls-engine-parts-and-accessories.aspx
Lots of billet accessory drive kits and other sundries. In other words - freshwater use only for those parts.
Finally heard back from the owner. Mechanic says 6 cylinders are 180-185, one is 165, and one is 135. Only did a compression test, no leak down test. Mechanic "thinks it's top end" and quoted "about $2500" to repair.
I'm leveraging that number as my discount on the agreed price. I figure either the mechanic is right and I can fix it myself for less...or that covers half the cost of a brand new warrantied longblock with tin. In any case, I think I'm moving forward with the purchase unless he just balks.
EDIT: Those numbers seem funny to me. Isn't 180-185 high for a stock 350? Also, the ammeter test only showed one down on compression, I suspect the 165 may be okay.
Interestingly enough the factory test spec for Mercruiser says the failure point is having one cylinder that is less than 70% the value of the highest - and even the 135 jug passes that spec.
In reply to ultraclyde :
Compression depends on a whoooole lot of factors. If the cam has an early valve closing (maybe tight lobe center, boats don't need to idle or cruise smoothly) that will raise cranking compression.
Did they provide info on which cylinders were low? I'm just curious if they are adjacent or similar locations (like 6/8 or 7/8)
Just got that. Front cylinder on starboard side is 165, second cylinder on port is 135. All others are 180-185.
It's not adjacent cylinders, so probably not head gasket. id bet the 165 is sticky rings from only being run 20 hours in 5 years, and the 135 is on one of the cylinders where the valves rust if the risers leak.
feom the mechanic:
also...he took my offer. Looks like I'm buying a boat. Have to schedule pickup but hopefully this Saturday. Retrieval and build thread to come!
In reply to ultraclyde :
Dare you to Jag V12 swap it.
The ammeter test only showed one low enough on compression to dramatically decrease the starter load. It looks like there could easily be a 10% variation between the other cylinders which is what we're talking about.
Boat motors are cammed for peak power at a relatively low RPM which will give you a fairly high cranking compression so I think those numbers a reasonable. Also, as a very general rule of thumb a cylinder with 100 psi of compression will fire which is why the problem doesn't show up as a noticeable misfire.
Stampie said:
In reply to ultraclyde :
Dare you to Jag V12 swap it.
Ha. Not a chance in hell I'm going off shore in something powered by a single Jag engine!
ultraclyde said:
Stampie said:
In reply to ultraclyde :
Dare you to Jag V12 swap it.
Ha. Not a chance in hell I'm going off shore in something powered by a single Jag engine!
that would be like having a race car with only one MSD box on it.
Congratulations on the purchase. Check the oil, fill the tank, get it warmed up, take it out and run it like you stole it for a couple of hours. Then do it again. Change the oil and try the compression test again. It’s been sitting, you’ll be surprised what a good hard run can do. Worst case, enjoy it as is for the rest of the summer and toss a long block at it this winter. That’s a really nice boat and worth some investment. Replacement value even before the current craziness would be north of $100K.
In reply to 11GTCS :
Thanks. Original list as this one is optioned was around $90k in 2000, so $142,000 today. Current 25' dual console models from Pursuit and Grady are well over $150k
Makes this boat seem cheap, but I'm not sure it's a fair comparison LOL
In reply to ultraclyde :
IMO your Pursuit is a way better built boat than Grady White. My nephew works in a high end boat repair shop, lots of stories of warranty issues with very very expensive Grady’s...
Agreed, but Pursuit has their issues too. It's funny how the best names in boating are still at quality levels that would embarrass even lackluster auto makers.
