When is an engine gone beyond rebuild?

[tiku]

Hi!

This is a another newbie question but bare with me guys..

What thing should I be checking from the engine block to see if my engine has gone beyond the point of no return?

How do I know that there's still enough material left to make the rebuild worthwhile? my mechanic told me that as mine is raw water cooled and from 1976 it's pretty much gone already (coolant water passgaes corroded excessively). Naturally I disagree with him because he has not seen the block yet.

 

[mcleaves]

Re: When is an engine gone beyond rebuild?

If the present engine is done, given the price of a short block or even a long block vs. a rebuild of something that age why would this even be a question? She has given plenty of service. Even if the passages are OK now, you have no idea what fatigue is lurking, even if you have the block magnufluxed.

I think your mechanic probably has good instincts. For the small differential in the price of a long block vs a rebuild of something as old as yours he's steering you toward a longer term solution.

If it were me that's where I would be headed anyhow.

As for what "thing" to check, there is no one thing. You have do a compression test which can indicate bad rings, valves, head gaskets or all of the above. The crank journals probably need a going over. The list is pretty long. Timing gears/pulleys and belts/chains (whatever your engine has). Camshaft may need grinding. The list goes on.

Why are you asking in the first place. Is the engine dead?

M

 

[Fishermark]

Re: When is an engine gone beyond rebuild?

Naturally I disagree with him because he has not seen the block yet.

You don't say where you boat. Salt water or fresh? Regardless, I would disagree as well. No one can tell just from the age. You have to pull it apart and see what it looks like. If you can do the work yourself there is no down side to this. What does it cost to check it out? I recently rebuilt an old 165 (straight six) engine. Looked bad on the outside, but the internals, including the water passages looked great. Can't know till you look.

 

[JustJason]

Re: When is an engine gone beyond rebuild?

look at it this way.... it takes a couple of hours to measure everything out once the block is bare. (2-3) Then it takes an hour or so do to all the math of what everything measures out to be, and what you want them to be. (1) Basically your figuring out the all the oversizes. Then... it goes to the machine shop for a couple of hours of boring and honing. (3-6) Then, when it comes back, you have to re-measure everything to make sure the machine shop got it correct. (2-3)
Then you have to fit all the pistons and rings. (1-2)
Then you have to assemble the rest of the block (2-3)

At 60-100 bucks an hour that's an awefully lot of hours. at anywhere of 11 to 18 hours worth of work to do it the right way.

 

[mcleaves]

Re: When is an engine gone beyond rebuild?

You don't say where you boat. Salt water or fresh? Regardless, I would disagree as well. No one can tell just from the age. You have to pull it apart and see what it looks like. If you can do the work yourself there is no down side to this. What does it cost to check it out? I recently rebuilt an old 165 (straight six) engine. Looked bad on the outside, but the internals, including the water passages looked great. Can't know till you look.

I presume if he can do the work himself he wouldn't be asking the basic question of "what do I check"?

I know much what to check and I wouldn't be attempting to do a rebuild on my own. Assume he is going to pay for new parts machining and assembly. THAT is your downside. It's a 30 year small old engine in a little speed boat. If it's acting up it's time to move on..

M

 

[mcleaves]

Re: When is an engine gone beyond rebuild?

Jason said it better than me with real numbers.

M

 

[Fishermark]

Re: When is an engine gone beyond rebuild?

I know much what to check and I wouldn't be attempting to do a rebuild on my own.

Well, there you go. I guess that's what makes us different. YOU may not attempt it... the original poster may not want to attempt it... I have not only attempted it, but have successfully done it.

I'm not trying to convince him (or you) whether or not to attempt it. Yeah, you and captJason both bring up a good point that if you have to pay someone to disassemble and check it out, then it may not be worth the time and money. But note what I wrote:

If you can do the work yourself there is no down side to this.

 

[fishmen111]

Re: When is an engine gone beyond rebuild?

Only way to know is to tear it down and start measuring with a calibrated micrometer and "t-bars". Of course all your wear pieces will be replaced (bearings/rings/timing chain/oil pump/cam). The measurements you will need are each cylinder's bore measured top and bottom at 90 degrees then 180. This will determine if the block is able to bored to 0.010/0.0030/0.0060 to clean up any scoring, out of round and/or taper. You need to mic your crank journals to determine if it must be reground. I do not suggest turning a crank more than 0.0010 under, though I am sure some see no problem grinding it down further. In my opinion, it just weakens it too much. Each model engine has specific specifications for clearances that may be obtained in manuals and online. Tiku, these are the starting points of determining if you have a rebuildable core. As others have stated, it may make more sense to just get another one. One alternative that I am sure to get shot down for is the "backyard rebuild". Tear it down and if the clearances come in out of spec...but close, replace just the bearings and rings and go for it. If it blows, you are out under $100. Just a thought.

 

[JustJason]

Re: When is an engine gone beyond rebuild?

You can always role the dice.... and that's your choice......

And T-bars stink.... you really want to do it with a dial bore gauge

 

[Bondo]

Re: When is an engine gone beyond rebuild?

How do I know that there's still enough material left to make the rebuild worthwhile? my mechanic told me that as mine is raw water cooled and from 1976 it's pretty much gone already (coolant water passgaes corroded excessively).

Ayuh,...

The Only way to find That out is to strip it down,+ have a Machine Shop Sonic Test the block...

 

[mcleaves]

Re: When is an engine gone beyond rebuild?

Well, there you go. I guess that's what makes us different. YOU may not attempt it... the original poster may not want to attempt it... I have not only attempted it, but have successfully done it.

I'm not trying to convince him (or you) whether or not to attempt it. Yeah, you and captJason both bring up a good point that if you have to pay someone to disassemble and check it out, then it may not be worth the time and money. But note what I wrote:

I don't disagree it's possible to do it. Just doesn't sound like he's gonna be the one to try given the implied knowledge from his post. There are lots of things I am willing to do but wouldn't necessarily suggest that becasue I can do them anyone can or should.

I applaud you for having the skill set to take on an engine rebuild with getting all the tolerances and machining correct. But that is a whole new ballgame from what most backyard mechanics can do.

I am just being realistic. If the engine is ready for a rebuild and from his question it doesn't like like he can do it, the best option is a new/reman long block vs the price and risk of dealing with someone working on his 30 year old engine. Again, just my opinion. Maybe he should tear it down and learn on this block.

M

 

[tiku]

Re: When is an engine gone beyond rebuild?

Thanks for the answers...

Ok, this is my first try ever on an engine rebuild, in fact my first serious mechanic attempt ever.

The engine has been taken to pieces, a friend of mine who builds race cars says that its not that bad. Unfortunately he hasn't got any experience on marine applications.

The main reason why I'm considering the rebuild is that this engine blew its headgasket and prior to that suffered from blowby. I have started this project nearly a year ago (have another post about the subject) but for various reasons I have not had the time to do anything until now.

So, all in all this is a practise run. My friend will guide me through the rebuild but I was worried about the state of the block when I got the marine mechanics view on things -> buy a new one!

If its money well spent or not I will take the block to a machine shop and see what they say. If it seems ok, boring (honing if I'm lucky) and planing for the block as well as cylinder head is the way to go. Naturally I will put new stuff in (bearings, valves, etc..)

The boat has been used in the Baltic Sea where salt content is lower than in oceans. Don't know if helps much to increase the life of a marine engine or not...

 

[mcleaves]

Re: When is an engine gone beyond rebuild?

Thanks for the answers...

Ok, this is my first try ever on an engine rebuild, in fact my first serious mechanic attempt ever.

The engine has been taken to pieces, a friend of mine who builds race cars says that its not that bad. Unfortunately he hasn't got any experience on marine applications.

The main reason why I'm considering the rebuild is that this engine blew its headgasket and prior to that suffered from blowby. I have started this project nearly a year ago (have another post about the subject) but for various reasons I have not had the time to do anything until now.

So, all in all this is a practise run. My friend will guide me through the rebuild but I was worried about the state of the block when I got the marine mechanics view on things -> buy a new one!

If its money well spent or not I will take the block to a machine shop and see what they say. If it seems ok, boring (honing if I'm lucky) and planing for the block as well as cylinder head is the way to go. Naturally I will put new stuff in (bearings, valves, etc..)

The boat has been used in the Baltic Sea where salt content is lower than in oceans. Don't know if helps much to increase the life of a marine engine or not...

If you have someone with rebuild experieince to work with you by all means take advantage of the chance to learn.

I would not spend a dime on anything else until you get that block checked out. 30 years in salt is a long time and nobody can look at a block form the outside and tell you it's fine. That's no better of a guess than the mechanic who said it was junk. So yes that will be money well spent. If it's junk and you are hell bent on doing your own rebuild there are a million of those engines out there that can be had for nothing as a base.

Good luck and let us know how it goes

Mike

 

[mylesm260]

Re: When is an engine gone beyond rebuild?

To answer you question in very few words:

Cracked block or Spun Mains


Cracked block is pretty self explanitory

Spun crank bearings require line boreing and odd-ball bearings, as well as crankshaft polishing.... Usually adds up to more than what a new engine is worth.