Blue smoke during warmup

[beech2000]

Hi all,
It's been awhile since I've posted. I now have an older Searay 350 with Q-Jet Carbed Merc V-Drive 454's.
Port engine during colder months (55F or below) blue smokes the marina up during initial warm up with typical scent of burning oil. Also oil gets very dark between changes which I do often.
I performed compression check and getting 78-81 PSI on all cylinders with WOT.
Plugs were dark but not shiny. I then suspected hot exhaust hoses from lack of cooling water but nope cool as can be. I've replaced the impellers on both engines and while they looked worn all fins were present. Still the same scenario.
Also know It appears I'm getting good water flow from exhaust when disconnecting. Engines are closed cooling. I guess next step is leak down test which is diffictult as I don't have a way to provide compressed air at the end of my dock. Engine runs great once warm. I'm suspecting valve stem seal or seals, or oil scraper rings. Any thoughts greatly appreciated.

 

[Bt Doctur]

your about 80 psi per cylinder shy of a good motor

 

[Scott Danforth]

compression should be 150 psi. below 125psi you start to loose performance

while mercruiser says you should rebuild at 100 psi, I like to rebuild at 125psi.

at 80 psi, your motor is toast

 

[beech2000]

Well. I guess I'm spending money. I expected some but wow.
Bad news is I used my shop compressor to verify my Mac Tools compression tester and both gauges read the same. So looks like toasted 454's. LOL. What can I do... Thanks

 

[beech2000]

compression should be 150 psi. below 125psi you start to loose performance

while mercruiser says you should rebuild at 100 psi, I like to rebuild at 125psi.

at 80 psi, your motor is toast

16 cylinders all well below 100 PSI.. One would think bad compression tester right?

 

[Rick Stephens]

All

16 cylinders all well below 100 PSI.. One would think bad compression tester right?

All too often true.

 

[Scott Danforth]

16 cylinders all well below 100 PSI.. One would think bad compression tester right?

except you tested the gauge.

 

[Bondo]

Ayuh,..... Sounds like you need a pair of long blocks, if all yer accessories are Ok,....

 

[beech2000]

Ayuh,..... Sounds like you need a pair of long blocks, if all yer accessories are Ok,....

Thanks,
So strange how all 16 cylinders are within 5 psi but low on compression. Going to check again with friends OTC compression tester just to be sure.
Doesn't really matter as I'm in agreement engines being due rebuilds and run like poop. Smokey cold morning port engine start up for 10 min. Port side in and out clanking. Not sure if valves, lifters, Piston pin or rod.
I have her scheduled for pull out next Tuesday.
Planning on using D&A machine shop in Canton, GA. They do everything in-house and will dyno test them for leaks and power. They have a great marine and race rep. Not cheap though. Looking at $12,000K when its all said and done.

 

[Scott Danforth]

12k is a lot of money for two rebuilds. I would inspect everything prior to buying parts.

Line hone and decking is a must. I also recommend zero balancing

A new crank is about the same cost as reconditioning the stock crank, and new rods are cheaper than reconditioning.

I would seriously consider building strokers. The difference in cost is literally the 1 hour of time to clearance the block rails for the extra 1/4" of stroke as the rotating assemblies are within $50

Without trying, you should be able to go from the 350hp rating to well over 450 without stroking. Add about 40hp for the extra stroke.

Make sure to spring for coated bearings. I was lucky, the machine shop that I used is family to Scotty at innovation marine and I could get their custom coated bearings

 

[beech2000]

Will do. Thanks for the recommendation. I'm having Andy build the engines for reliability and not performance. I need them to run until I'm below the dirt or the boat sinks. (Which ever comes first).

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Whilist they are a performance engine machine shop, Andy has built many big blocks, LS, and SBC on the local front for marine use. They typically will dyno run the engine all day for the customer. Why? because Big 40 foot boat haul outs and engine R&R's are a big deal. He gets it!

 

[Scott Danforth]

since your boat is a 1990, you either have a Mk IV motor (2-piece RMS, flat tappet cam) or a Gen V motor. if its a gen V i would recommend upgrading to Gen VI (1996 and later) the 1990 Gen V blocks are the first year of priority mains oiling and there were goofy issues with the steam holes and the decks.

talk to your machinist.

 

[beech2000]

Already know the answer to this. Engines are the original serial numbers to her and Mark 4's. Thanks

 

[QBhoy]

How much oil do you have in these motors ?

 

[tpenfield]

If the boat is 1990 and original motors, I'm thinking the engines are the Mark 4 version (Stamped steel valve covers . . . i.e. 'rounded style') are telltale of the Mark 4 engines.

$12K does seem pricey, but if it includes removal and re-installation, then not so much. The biggest issue with the 454's is that they are pricey to rebuild/replace since they are out of production.

 

[JustJason]

I would do the leakdown test next. The engines might only need a valve job.