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Need help with compression reading - replace engines or keep ???

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contender31

Regular Contributor
Morning I have 2 1990 Crusader 454 350 hp carburated FWC engines with 1350 hrs on each. I recently bought the boat and am considering repowering due to recent mechanical failures. Yesterday I did a compression test and need your opinions on the results - ok here goes -

Port Engine # 1-132, #2-135, #3-130, #4-110, #5-130,#6-130, #7-110, #8-140 -- Starboard - #1-115, #2-110, #3-90, #4-100, #5-105, #6-85, #7-130, #8-120.

These numbers were done with a cold engine. Could not due a hot engine test due to the heat generated in the engine room. My question is simply this - does one run these engines until they die or replace now before they die? The options for replacment are as follows - 1. long blocks - , 2. redo the heads, 3. swap out the old engines with lesser hr used engines ( note - I have a line on 2 engines with appr 400 hrs on them). Does anyone have any experience with US Engines.com ? they claim that they can increase the hp to 420 and increase the torque from 300 to 500 on these 350 hp engines.

Your comments would be greatly appreciated

Thank you in advance
 
Further the used engines come complete with borg warner transmissions and one other option is replacing with bobtail engines complete with remanufactured block and all new coolant, exhaust and electrical parts.

Thanks
 
Is the starboard engine pretty lumpy at idle? Rattling transmission at idle in gear? In any case, its numbers don't look so good. The typical next step is to squirt in a tablespoon of engine oil into those lowest reading cylinders and remeasure compression. Unless, you can do a leakdown test. This will drive the next decision: top end job or total rebuild or ... The port looks to be livable for a while longer.
 
Thanks for the reply - not sure what you mean by lumpy? , yes the transmission does growl when engaged, the port engine is quite. What will the oil shot into the cylinder tell me? What would you suggest if I decide to change out the engines of the three I gave in my first post? I was thinking if I had to go to the trouble of one engine I might as well do both with the amount of hours on each engine.

Please feel free to be frank

thanks
 
"lumpy" meaning not very smooth. As your starboard engine fires, it has strong cycles and somewhat weak combustion cycles during its rotation. This can usually be heard by a trained ear, and the transmission is also sensitive to this at very low speeds. The oil squirt is a classic test for determining if the loss in compression is caused by the valves or the piston rings. The oil temporarily seals the worn ring and get you higher compression numbers as a result. However, the oil shot won't affect the reading if the exhaust valve is burned, for instance. If at least a 15psi increase in pressure is a result of the oil squirt test, you know that to fix that, the engine is coming out.
I can't really answer your "what to spend the $ on" question. For myself, I tend to do as much as possible myself. I keep the boat in the back canal, and have a davit for ready use to pull engines. I can have a 454 in my backyard in about an hour, and can work on it at my leisure for weeks with no yard bill. I'm a "shade tree mechanic" and have a mango tree to prove it! I have a local, trusted machine shop, and I even have a friend I borrow an engine stand from. Over the years, I've collected just enough special tools to deal with just these engines. Not a lot of stuff, but tools include bore gauge, ring expander, ring compressor, dampner installer, wheel puller, torque wrenches, calipers, and the usual set of "standard" tools and an air compressor. A full rebuild takes me about 3 weeks, mostly gated by the bore job at the machinist shop. I like the idea that I'm not inheriting a reworked engine with possible other issues, like an ex salt water cooled block. In the meanwhile, I sandblast rusty bolt-on parts and paint stuff...
If, on the other hand, I was forced to haul the boat at a yard, and then start an engine job, the story would change. I'd have a long block ready.
If I had a lot of $$ to spend on this, I'd have Yanmars in there. So, the solution can take many forms.
 
Per the GM spec, both are due for an overhaul. DD's recommendation for the next steps are key to determine the viable options for the solution. The rule-of-thumb we used to use in the shop was to expect to do the top end around 1000 hours. You are well over that and hopefully that will prove to be a viable fix.

I'm from the DIY school as well. When I'm done, I know what I have and can only blame myself if something goes wrong. Though I trust my machinist, their work is always verified.

I believe in keeping things running efficiently. Running them til they die could waste lots of fuel and given the current rate, it doesn't take too many gallons to buy a few hours at a good machine shop. It could also cause aditional wear driving the total repair cost up unnecessarily.

Unless you use the boat commercially (daily or close to it), I doubt you'd ever come close to recouping the costs for the diesel swap.
 
Thanks to give you my scenario - I also live on the water and somewhat handy albiet not to your extent. I would be using the assistance of a qualified mechanic in tandem with my labor. My choices are 1. to the yard to switch out the engines or 2. tear it down in my back yard and redo the heads. Either way I am spending money but the smart money may be replacing the engines with either remanufactured long blocks or bobtailed remanufactured. I have estimates all inclusive installed including the yard of $15K long blocks or $17K for bobtail. The benefit to the bobtails are they are totally remanufactured and include all new exhaust, cooling and ignition parts. The long blocks will require me using my old parts off of my current engines. Not sure if I like that idea - putting old parts on a new engine? The in the boat head job would run appr. $5K but again old parts and a lower block with 1300 hrs on it. Tough decision :(

Now what do you think?
 
It seems what your saying is oil test cylinder # 3 and 6 on the starboard engine? If the compression rises 15 lbs or more than the choice is to replace the engines as noted. If the reading is less than 15 lbs higher than the head job is the choice. Is this an accurate assumption? What is your best guess on longevity if nothing is done considering I run at 3,000 rpm or less? Oh they sit in a 1990 Tiara Open at 14k lbs. When running correctly they plane at 22 mph @ 3,000 rpm

Thanks
 
OK, so you need to do the oiled compression test to find out if this rebuild is going beyond the top end. 1350 TT seems a bit low to need a bore job, IF properly maintained.
A lower end with 1300TT AND good compression AND no bearing noise is nothing to worry with.

sorry; got distracted at work!! yes, on your understanding of the oil test. How many hours per year do you estimate?

2nd edit: I would do a new cam, lifters, and replace that stock timing chain and sprokets with a Miloden (sp?) true roller type, even as part of a top end only job.
 
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Thanks to answer your questions

1. I boat appr 100 hrs a year
2. I just priced out the top end - $ 300 per engine to redo the heads, 12 hrs labor in and out, not including the parts you mention to replace - any idea how much they cost?

I am going to do the oil test per your rec - do I need to do just the weak cylinders? All my cylinders are with 20 of the 130 rec except cylinder # 3 @ 90 and # 6 @ 85. All others are 110 plus on both engines as stated on my original post.

Thanks
 
If you need a very good machine shop, not too far away from you: check out S. Fl Crank and Machine, in Lake Worth. Top notch. They do boring, head work, crank turning all at their site.
If the free play on the existing chain is over 1/2" persue the Miloden chain and sprocket set. 1300hours on OEM chain is fairly high. I don't think it will go to 2600. I buy this stuff and the gaskets from PAW out in CA. Pricing good, service not so.
I forgot to ask what the oil pressure is when at cruise and at hot idle. That might affect decisions.
yes, just test the weak cylinders; although doing all won't hurt a thing.
 
Question - is it absolutely necessary to remove all the plugs before starting the compression test?? I did not remove all the plugs the first time around - should I remove them and redo the test again or do I trust my original readings taken?

Thanks
 
Wierd thing is the oil pressure reads consistent at 40 on the engine with lower readings and the other reads 40 at startup and fluctuates between 20 and 40 depending on the rpm.
 
contender31 said:
Question - is it absolutely necessary to remove all the plugs before starting the compression test?? I did not remove all the plugs the first time around - should I remove them and redo the test again or do I trust my original readings taken?

Thanks
Click to expand...

Having some plugs in will reduce the cranking speed, which can affect readings. Pull all the plugs, force choke open, WOT, coil output to ground.
 
contender31 said:
Wierd thing is the oil pressure reads consistent at 40 on the engine with lower readings and the other reads 40 at startup and fluctuates between 20 and 40 depending on the rpm.
Click to expand...

40 is fine, but what happens after a 30 minute cruise and you go to idle, in gear? That pressure can tell something about bottom end bearing clearance. The port eng pressure is usually a function of rpm?
 
If you opt for the new cam parts - great idea - don't forget the RH engine has some differing parts so DON'T order two of everything. The cam will be different and you'll need a timing gear set (gears only - no chain).
 
If it were me looking at your situation, I would order up remanufactured long blocks tomorrow. The labor to pull and replace is about the same as for rebuilding existing engines.
There may be excellent machine shops out there, maybe even one in your area that will do great work promptly. They are usually way backlogged when you show up. The vast majority tend to be run by people who are far better machinists than businessmen and they tend to take FOR EVER to get to your project. Calling and bugging them merely prolongs the time. Heaven forbid you do anything to piss 'em off or you can just about forget ever seeing your engines ever again. With them holding your parts hostage you have no option of trading in your cores on a new or rebuilt engine. It could be three to six months before you get your engines.
Been down this miserable path enough times to say cut your losses now and place the call. Have the yard do it if you feel better letting them do the legwork (and tacking on a little kickback for their trouble)
 
Just my (amature) 2 cents: Still, it sounds like you may still need to do a really good compression test. Myself, I would try to not make these decisions without good data since it is available. When I do a compression test, I've always done it on a warm engine, plugs out, trottle and choke open. Then, if I get number I don't like. I try the oil in cylinder thing to get further data. A bit of a valve job is one thing. Redoing an old marine block is another.

Also conisder warm idle oil pressure as that can tell you some things about bearing clearances and such.

And if they sound like they are junk, they are junk.

Good luck with hard/expensive decisions.

Bruce Clarkson
 
If you were me I would unfortunately ignore all you have done so far. Run the engine for an hour, bring it back to the dock, have an ice cold beer then do the compression test again properly(per diver Dave's instructions). Make sure you have a new gauge. Given what you are going to spend a new gauge is cheap. A 33 Tiara isn't too much boat for 454's. They should go 2000 hrs. Do they burn oil? blue smoke at startup or at 3000rpm? Can they turn up to 4200rpm? If you get poor numbers again(although the one side isn't too bad) then do the tbspn of oil technique, then decide what to do. I'm not a big fan of the snake oil stuff but maybe put a can of seafoam in the oil and run it for 25 hrs or so and see what happens with a new compression test. If you are going to replace them anyway.....
 
Thanks to all who are replying I appreciate your input -- ok I went out on a hunch and purchased a new pressure gauge $ 29 and the results were much different than before. I tested the bad engine and here are the results. Starboard Engine - # 1 old reading-115 - new 140, #2 old 110-new 150, #3 old 90- new 120, #4 old 100-new 130, #5 old 105 - new 125, # 6 old 85 - new 110, #7 old 130 -new 145, #8 old 120 - new 130. I pulled all the plugs before the test and it was done on a cold engine. Ok what are your thoughts on these new numbers? I didnt do the other engine as those numbers were much stronger and based on what I am seeing the numbers are all much higher on this engine than the first time. Incredible - new gauge brings much different results.

Please feel free to throw in your opinions - they are all respected immensely- thank god for the internet:)
 
I suspect the choke being closed would be less of an issue than the cold engine. Those numbers really are not that bad. If the 17 grand is burning a hole in your pocket spend it. Otherwise I'd run it as is. How much oil does it burn? Any blue smoke at 3000 rpm?
 
contender31 said:
Note : I didn't hold the choke open on this test - would that have made a difference in my readings?
Click to expand...

If the choke is closed during cranking, then it willl cause a pressure drop across the carb as the piston is trying to pull in a charge. Pin the choke open and run this again. Then we will all know for sure what is going on.

Either that, or run this boat long enough to find out WOT rpms, oil consumption, oil leaks, blowby, bad bearing noises, and idle smoothness. I'm going to say that a number of us are not sure why a compression test is called for, unless this is a baseline measurement. (not a problem just sayin..)
 
The direction for taking compression in my 1990 Crusader manual says to operate the engine until it has reached proper operating temperature. This may have changed in more recent years. Remove all spark plugs, remove and ground the high tension lead from the distributor. Ensure that the throttle and choke are fully open and install the gauge in the #1 cylinder. Crank the engine for the number of COMPRESSION strokes needed to obtain the maximum reading (usually 5-6 strokes). Repeat the test for each cylinder, cranking the same number of times as was done on the #1 cylinder. The results section says a uniform variation of +-20 psi from 130-170 is permissable, however the compression on all cylinders should be uniform within 10 psi. Your new test results are better than the previous test but still not withing these so-called requirements.

There is also a manifold vacuum test that states that the vacuum of a warmed up engine wehn running at 750 rpm in neutral should be between 12 and 15 inches of vacuum. This test is useful when adjusting the mixture screws on the carb.

Erich
 
diver_dave said:
If the choke is closed during cranking, then it willl cause a pressure drop across the carb as the piston is trying to pull in a charge. Pin the choke open and run this again. Then we will all know for sure what is going on.

Either that, or run this boat long enough to find out WOT rpms, oil consumption, oil leaks, blowby, bad bearing noises, and idle smoothness. I'm going to say that a number of us are not sure why a compression test is called for, unless this is a baseline measurement. (not a problem just sayin..)
Click to expand...

What do you mean by a pressure drop? are you saying that the compression reading could in fact be higher than noted if I hold the choke open?

Thanks
 
contender31 said:
What do you mean by a pressure drop? are you saying that the compression reading could in fact be higher than noted if I hold the choke open?

Thanks
Click to expand...

Yes. Theoretically the closed choke is not allowing all the air there could be entering the cylinders. Not enough air to begin with would lead to a lower compression reading. Don't take this the wrong way but you ask people their opinions, they give you good advice but you don't take it. You sound like me after I leave my physician. LOL
 
sammi said:
Yes. Theoretically the closed choke is not allowing all the air there could be entering the cylinders. Not enough air to begin with would lead to a lower compression reading. Don't take this the wrong way but you ask people their opinions, they give you good advice but you don't take it. You sound like me after I leave my physician. LOL
Click to expand...

Nothing ever taken persoanally unless your attacking my family:) just trying to learn here
 
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