Stuck! Need advice ASAP 7.4 motor knock- need to get home!

Russ,

I never saw this thread until now. Wow.....what a rollercoaster with the yard. I'm glad you found a good place and things are moving now toward getting the boat fixed.

I'll let the pros comment with more technical suggestions, but I'll just give you my opinion on the overall picture.

Option 1 ($12K for new motor) - I assume it's for the brand new one. If my assumption is correct, how much is it for a completely rebuilt motor? In any event, I would consider replacing the whole motor option as a last resort.

I would consider option 3 ($4K) as the primary and then option 2 ($7K). I hope you get some good feedback from folks that know these engines and can explain in more details the risk of performing opt#3 vs. opt#2. So far it sounds like opt#3 should work fine. While collecting all opinions I think the question "how long are you planning to keep the boat?" can help in decision making process. For example, your formula may look like this:

Opt#1 ($12K) = 10-15YOS (years of service)
Opt#2 ($7K) = 5-10YOS
Opt#3 ($4K) = 2-5YOS

In case if you're thinking to move on to a different boat in the next couple of years, then this is where 80/20 rule (invest 20% of an effort to get 80% of result) may work for you.

Also, another thing that can help you with the decision making is the the warranty for each otpion. For example, if opt#3 gets you 1-3months and opt#2 gets you 6-12months that may give you much more comfort level.

Just thinking loud and hope it helps a little.

Good luck my friend.
 
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Russ,

I would either 1)leave the piston as is (from your post it semms like the piston is beat up but there are no holes in it and the ring land is not comprimised) and just fix the head/get a replacement and call it good until repower time (both sides) or 2) have the entire motor rebuilt (bored, 8 new pistons, regrind crank, new guides, valve job, etc) this will not cost even close to 12k and will give you a new motor.

I would not replace one piston in the existing motor - a lot of labor/cost and you still have a used motor!

Where is it? Gwenmor? Brewers?
 
have done option 3 about 2 years ago to my friends Carver.he dropeed a valve and it put a few small dimples in the top of the piston.depending on the extent of the damage and there was no cylinder wall damage,I would not think twice about replacing the heads and off you go.did the valve head bounce around in the cylinder or did it embed into the head.the one I did the valve head was embedded into the valve seat so it didn't touch the walls at all.boat runs better then ever after the repair but 4K seems steep.I did the whole job for about $800 for rebuilt heads,gaskets and my labor was beer and a good dinner after.
 
Russ, You have a beautiful boat, and with 700 hours I would go with a new engine option. You will probably have to replace the other engine in a year or two, but your boat would be like new, and since it is the Last Dance, you have to make it last...
 
Russ, the consideration, I think, is that these motors are no longer made. A new motor today on only one side would not mean you will be able to find a twin in a year or two. Better to do both at the same time. Big bucks, I know, but if you start saving up now when the time comes, it will not be so big an expense. Alternatives might present themselves in the meantime.

I would not do alternative #2 either. You want the motor to be balanced and with this procedure, you might as well rebuild the entire motor. The labor would be close and the only diff would be the parts.

If the valve bits did not impact the cylinder walls or the rings at all then option #3 would be best. Then start saving now for a complete re-power in a year or two or three. In terms of a re-power, the 370 setup is pretty good as there is good access to pull the motors without too much trouble. All you need is a good crane. I re-powered my last boat with new small blocks and that was a big learning experience. It was a correct choice then, but you have to make sure the economics make sense. Who knows, you might get foot-itis and we'll see you in a newer 420 or 44.

BTW, if you're looking for a new marina, there's an empty slip next to me in Westbrook. Sea Ray dealer is right next door.

Gene
 
Alex F said:
Russ,

I never saw this thread until now. Wow.....what a rollercoaster with the yard. I'm glad you found a good place and things are moving now toward getting the boat fixed.

I'll let the pros comment with more technical suggestions, but I'll just give you my opinion on the overall picture.

Option 1 ($12K for new motor) - I assume it's for the brand new one. If my assumption is correct, how much is it for a completely rebuilt motor? In any
event, I would consider replacing the whole motor option as a last resort.

I would consider option 3 ($4K) as the primary and then option 2 ($7K). I hope you get some good feedback from folks that know
these engines and can explain in more details the risk of performing opt#3 vs. opt#2. So far it sounds like opt#3 should work fine. While collecting all opinions I think the question "how long are you planning to keep the boat?" can help in decision making process. For example, your formula may look like this:

Opt#1 ($12K) = 10-15YOS (years of servic
Opt#2 ($7K) = 5-10YOS
Opt#3 ($4K) = 2-5YOS

In case if you're thinking to move on to a different boat in the next couple of years, then this is where 80/20 rule (invest 20% of an effort to get 80% of result) may work for you.

Also, another thing that can help you with the decision making is the the warranty for each otpion. For example, if opt#3 gets you 1-3months and opt#2 gets you 6-12months that may give you much more comfort level.

Just thinking loud and hope it helps a little.



Good luck my friend.
Click to expand...


Alex, thank you, although we think very much alike it is good to know and get confirmation that I am on the right track! I will keep you updated.
 
Ididntdoit said:
Russ,

I would either 1)leave the piston as is (from your post it semms like the piston is beat up but there are no holes in it and the ring land is not comprimised) and just fix the head/get a replacement and call it good until repower time (both sides) or 2) have the entire motor rebuilt (bored, 8 new pistons, regrind crank, new guides, valve job, etc) this will not cost even close to 12k and will give you a new motor.

I would not replace one piston in the existing motor - a lot of labor/cost and you still have a used motor!

Where is it? Gwenmor? Brewers?
Click to expand...

Yes, just the piston. He is going to pour some oil in it to ensure but rings seem to be okay. It's at Gwenmor- thanks for your advice, I am leaning that way.
 
johngus said:
have done option 3 about 2 years ago to my friends Carver.he dropeed a valve and it put a few small dimples in the top of the piston.depending on the extent of the damage and there was no cylinder wall damage,I would not think twice about replacing the heads and off you go.did the valve head bounce around in the cylinder or did it embed into the head.the one I did the valve head was embedded into the valve seat so it didn't touch the walls at all.boat runs better then ever after the repair but 4K seems steep.I did the whole job for about $800 for rebuilt heads,gaskets and my labor was beer and a good dinner after.
Click to expand...

Too bad your not nearby! Marinas are expensive around here but then again I do not have any firm pricing yet. There did not appear to be any wall damage just 5 or 6 very small fragments embedded on top of the piston that we pulled off. Thanks for sharing your experience, very helpful.
 
rcknecht said:
Russ, You have a beautiful boat, and with 700 hours I would go with a new engine option. You will probably have to replace the other engine in a year or two, but your boat would be like new, and since it is the Last Dance, you have to make it last...
Click to expand...

Rod, thank you. It may be the Last Dance but it's not the last boat!
 
RubberDuckeeToo2 said:
Russ, the consideration, I think, is that these motors are no longer made. A new motor today on only one side would not mean you will be able to find a twin in a year or two. Better to do both at the same time. Big bucks, I know, but if you start saving up now when the time comes, it will not be so big an expense. Alternatives might present themselves in the meantime.

I would not do alternative #2 either. You want the motor to be balanced and with this procedure, you might as well rebuild the entire motor. The labor would be close and the only diff would be the parts.

If the valve bits did not impact the cylinder walls or the rings at all then option #3 would be best. Then start saving now for a complete re-power in a year or two or three. In terms of a re-power, the 370 setup is pretty good as there is good access to pull the motors without too much trouble. All you need is a good crane. I re-powered my last boat with new small blocks and that was a big learning experience. It was a correct choice then, but you have to make sure the economics make sense. Who knows, you might get foot-itis and we'll see you in a newer 420 or 44.

BTW, if you're looking for a new marina, there's an empty slip next to me in Westbrook. Sea Ray dealer is right next door.

Gene
Click to expand...

Gene, your last paragraph sums it up. That's the plan if all goes well from here, thanks for your input. Westbrook is not out of the question. Which marina? Cost per foot?

Thanks again
 
RubberDuckeeToo2 said:
Russ, the consideration, I think, is that these motors are no longer made. A new motor today on only one side would not mean you will be able to find a twin in a year or two. Better to do both at the same time. Big bucks, I know, but if you start saving up now when the time comes, it will not be so big an expense.
Click to expand...


True, they did stop producing these motors, but parts are going to be readily available for years to come. Just my opinion, but I would not let this sway your decision.

Russ - Can you provide some more detail on the failure? Did it drop a valve or was the valve sticking and the piston contacted it? Did the valve break and pieces ended up in the exhaust? Were you able to find all the pieces? It is imperative to find all the pieces, otherwise it could cause overheating down the road. If you can locate the pieces, I might consider just throwing on another head and calling it a day. If you're going to pull the motor to replace one piston, you might as well rebuild the entire motor.

Doug
 
douglee25 said:
True, they did stop producing these motors, but parts are going to be readily available for years to come. Just my opinion, but I would not let this sway your decision.

Russ - Can you provide some more detail on the failure? Did it drop a valve or was the valve sticking and the piston contacted it? Did the valve break and pieces ended up in the exhaust? Were you able to find all the pieces? It is imperative to find all the pieces, otherwise it could cause overheating down the road. If you can locate the pieces, I might consider just throwing on another head and calling it a day. If you're going to pull the motor to replace one piston, you might as well rebuild the entire motor.

Doug
Click to expand...

I agree 100%!
 
Russ,

Sorry to hear the details of your engine failure. I agree it is a tough decision, with several variables.

Option #2 is time consuming, and less than ideal solution. As others have said, if you are going to go through the trouble of pulling that engine to replace one piston, do the job right and just rebuild the entire engine. Bore and hone the engine (pay the extra few dollars to have it done with torque plates), new bearings, heads reworked, etc. etc.

Option #1 gives you a fresh engine with a warranty, and there is a lot to be said for that peace of mind. Change your manifolds and risers on both engines at the same time, and perform any other required maintenance, and you should be set for quite some time. 700 hours is only middle age for these engines, if they have not been abused, and the oil, filters, and other maintenance has been performed regularly and properly. On the other hand, 700 can be a lifetime for engines that are not well cared for. Only you know those answers.

Option #3 can work, but only a well trained and knowledgeable technician can make that determination. For example:

How worn are the cylinder bores?
How much do the bores deviate from cylindrical? (out of round condition)
Is any bore damage visible?
Is there a large ridge at the top of the bores?
Does your technician have the proper measuring equipment available to take these measurements? Or is he simply eyeballing the bores?
(A bore gauge is best, followed by an inside snap gauge and a 4-5" micrometer)

Assuming the bores are suitable, then a replacement head could be a fine solution. In this case, cleanliness is paramount. For example, since the head has been removed from one bank of this engine (or maybe both), the technician should have cleaned the bores, and then covered the engine with clan plastic sheeting, or lots of tape, to prevent contamination from entering the open engine. Did he?

Certain early gas big blocks suffered from the loss of exhaust seats that were pressed into the heads with insufficient interference fit. This problem tended to manifest more with high performance engines in go-fasts, but it applies to base engines as well. Over time, the exhaust seat can loosen and "fall out" of the cylinder head casting, and do all sorts of damage. I would want to know if you lost an actual valve, or the valve seat. If you have the heads rebuilt, be sure the machine shop of choice knows the heads are for a marine application, and installs the new seats with additional interference to prevent recurrence of this issue.

At any rate, good luck with the repairs - I know we all hope it works out for the best. If you like, send me a PM, and we can discuss the matter further over phone (I'll give you my number).

Dale
 
Russ, Here is another option. Do masterfab on your boat and put in 8.1 or 8.2s... Better yet go to Yanmars... We can do a collection on CSR to help pay for the engines... I will kick in $20...
 
rcknecht said:
Russ, Here is another option. Do masterfab on your boat and put in 8.1 or 8.2s... Better yet go to Yanmars... We can do a collection on CSR to help pay for the engines... I will kick in $20...
Click to expand...

Ya know, I just might do that just to get your $20! Don't tell Nancy!!
 
Doug, I have asked for more detail.

Dale, thank you - I have asked them the questions you provided. Regarding the motors they have been serviced
by a MC mechanic since day 1 from a SR dealer until I purchased and then with a MC mechanic with an open checkbook.

One exception, I replaced the manifolds and risers with OEM the beggining of last season. The previous OEM manifolds were done by the dealer 5 yrs prior- I figured it was time. At that time I noticed moisture intrusion and some light scaling in the port that is connected to the valve/cylinder that has subsequently failed a year and a half later.
 
Wow Russ. Sorry to hear of the issues with your old marina. Talk about insult to injury!
I am in agreement with the majority here. I would go option #3 if they give you ample warranty time to test it out. I do recall you discussing a bigger boat when we were at the MYC. If you will be in the market soon, I would take the least expensive, but mechanically sound, alternative. I have to say though, $4k sounds high to me too. I would think a rebuilt is only $5k or so, no?

Either way get that puppy running so we can eat, drink and be merry in Port Jeff before the snow sets in!!
 
Russ,

I do have an opening for one boat this winter......could be you! And remember, I charge less than a marina or yard...

Dale
 
MasterFab said:
Russ,

I do have an opening for one boat this winter......could be you! And remember, I charge less than a marina or yard...

Dale
Click to expand...


Dale,

I am sure transport alone would help make up the difference. I do like the idea though, two problems- cost and ROI. I'm not sure I could afford it and I'm not sure how long I plan on keeping her. What kind of investment are we talking to "Masterfab" the engines, bilge etc? Ballpark
 
I hope if you fix it you do both heads.If one is bad now,the other may follow soon enough.you are at most of the labor for one,I would go the rest of the way and make sure that engine has both heads done.would say after your repair,you'll be good for many seasons.the bottom end of a 7.4 is basically bulletproof and should go 2000 hours with good maintenance.
 
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