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454 Rebuild or done...?

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Blackfin27

Contributing Member
Circa 2000 454 Marine Power Vortec 330 HP with 960 light hours.

Engine had run well this past Summer, then some vibration and was laggy, did not push the RPM due to the lag and vibration. Starts were hard and substantial cloud of what I call steam or white smoke that would dissipate after warming.

New plugs, cutlass bearing, PSS shaft seal, oil change, dist cap, raw water pump then went in Summer 2023 and improved, most vibration eliminated, ran WOT to 4800 RPM, short bursts. Was hoping these measures would take care of the major symptoms. But, she was eating coolant and you could smell it in the engine bay, but ran pretty smooth.

Next up, different mechanic ran compression test calling it a 'fail' at 120-130. Elected to tear off the Risers (done and overdue) , replacement was way overdue, manifolds off. Evidence of water intrusion...this a FWC engine. Mechanic said he was concerned about glazing on the cylinder walls, he mentioned possibly lagging due to improper propping, the prop is good and tuned so that's not it.

So, possible poor compression due to water intrusion? Could try a top end rebuild with new pistons/gaskets etc. Labor and parts and still could end up with low compression-
Got quoted a full rebuild price of around $8,000, plus add all the hang ons get replaced, more parts and labor....24 year old engine.

Because she ran strong after the above mentioned work and hit WOT, cant quit wrap my head around it....but. I don't have the time or skills to rebuild myself. Given the labor rates at the yards these days, going with the minimum rebuild and not honing/boring out the cylinder walls and not going all in could still end up with low compression?

Strongly considering a repower, Merc 6.2 320hp, FWC with new gears, engines are on back order. Not many options out there for small blocks V8.

I'm wondering what you mechanics think given the circumstances....give it up and repower, sell the 454w/ gears and move on with fresh power...?
 
I would say a lot depends on your budget and 'wants'.

Going brand new will get your the full warranty but also introduce you to the EPA sanctioned world...it is normally the fastest route to a fully usable vessel but with the highest price.

Rebuilding what you have may/may not be viable depending upon how long the 'eating coolant' has been going on...you also have the old bolt-ons...

You can also get factory rebuilds (short blocks thru complete engines) as well as third party rebuilds.

I would also be inclined to make sure you understand why the old engines had issues .... and make sure the cause(s) is fixed before doing the repower....
 
Yes, I have a 6.2 Merc 320 HP on order, FWC NON catalytic. Ship date is April 8, supposedly. The 350 hp version comes with catalytic converter and fly by wire, no thanks. This seems to be the best option without getting into an Ilmor 6.2 which is significantly more expensive. The new ZF gears have less reach to the shaft flange so rebuilding the VD and mating the shaft. Just had the cutlass bearing replaced and new PSS shaft seal installed so Id hate to have to re-shaft....tapered 1 1/4". Strut was re-aligned.

Here were the Compression Test results on the 454 btw:

1-50, 2-150, 3-130, 4-120, 5-130, 6-120, 7-130, 8-120
Removed cylinder heads for evaluation, evidence of glazing. The block stamp indicates the engine was 1999.
Engine is out. New tanks coming in, hoses etc.

Thanks for your input as always.
 
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