Cylinder #4 is toast.... please help diagnose (w/ pics)

[JCF350]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

If you are going to have to bore the sleeve oversized then you should do ALL the cylinders. Not just one or two. If you do, the engines displacement will be out of "square" and the rotating mass will be out of balance significantly. The slight difference in weight with one larger piston will create a substantial vibration at rpm's above 1,200 and possibly even lower. The, "only do the cylinder/'s that are bad", is not a good fix unless you are wanting to off the boat to some sucker.

Not true on the vibration deal. Used to see different sized pistons in brand new engines also the factory rebuilds would come with 2 or 3 different piston sizes. Plus I have rebuilt more than few myself. This is the process called "select fit".
Also note that these were not after market pistons mixed with factory ones.

 

[Frank Acampora]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Nate: have you not seen my posts where I specifically explain that the oversized pistons are balanced to original factory weight? There is no extra weight so there is no vibration problem. In addition, the increased displacement of one cylinder is so small, that the engine will never notice it. Won't even appreciably change the compression ratio.

Example: the original Chrysler 105 from which this block is a direct copy, (with a stroker crank), had a bore and stroke of 3.3125 X 2.80 inch for 96.5 cu. inch displacement. The next series of blocks was the 115-130 with 3.375 X 2.80 for 100 cubic inches. SO, with the 2.80 crankshaft a difference of .060 bore only yeilds 3.5 cubic inches. or about 3/4 inch or so of displacement per cylinder. The stroker crank which this engine has (2.86) times the bore of 3.3125 will yeild only 98.6 cubic inches. An overbore of .040 will yeild only 1/2 cubic inch extra per cylinder or only about 2%. Negligible--the engine will never see it.

Most of the times, I over bore all cylinders because 2 or more need it so I might as well do all. However, even if money was a consideration, I might still do all four because one larger piston offends me aestheticly. I am the type of fellow who must have all screws the same length unless the difference is for an engineering reason. Nice to have things in even numbers also. Some people call it anal but I just think it is the mark of an orderly mind.

This is why it is not worth overboring these engines for more displacement and power--just won't do it-- might gain 2-3 hp for all that work.

 

[Nate3172]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

I have to disagree with you on this one Frank. I do not dispute that you have extensive knowledge and experience with engines. I also have alot of knowledge and experience with building race car engines for some of the guys here at the local track. There is going to be a difference with compression ratio's because he is installing new piston and rings on a fresh bore. This guy has extensive damage to that cylinder. Undoubtedly there is contamination throughout that entire engine. He should tear it completely down and clean it. If he has to go that far than he should do it right rather than a cheap fix that could come back to haunt him. If he doesn't have the money than he should save it until he does. If you have ever balanced and blueprinted an engine, than you do notice a difference and a considerable one at that. I'm not saying that he has to go to those extremes but out of "square" engine rebuilds are cheap rebuilds and no engine builder who takes pride in there work would settle for that. Maybe the oversized piston itself is close to factory spec, but weigh it again after you install the rings and tell me they are even close. Everyone may think I'm being too anal here, and that's fine, but my engine builds never fail unless I make a mistake by taking a shortcut. I use to take shortcuts when I was younger and it came back to bite me in the A@# alot. We should be encouraging this guy to do it right rather than telling him he can get by with doing it wrong only to have to possibly be tearing it apart again in the near future.

 

[JCF350]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

I have to disagree with you on this one Frank. I do not dispute that you have extensive knowledge and experience with engines. I also have alot of knowledge and experience with building race car engines for some of the guys here at the local track. There is going to be a difference with compression ratio's because he is installing new piston and rings on a fresh bore. This guy has extensive damage to that cylinder. Undoubtedly there is contamination throughout that entire engine. He should tear it completely down and clean it. If he has to go that far than he should do it right rather than a cheap fix that could come back to haunt him. If he doesn't have the money than he should save it until he does. If you have ever balanced and blueprinted an engine, than you do notice a difference and a considerable one at that. I'm not saying that he has to go to those extremes but out of "square" engine rebuilds are cheap rebuilds and no engine builder who takes pride in there work would settle for that. Maybe the oversized piston itself is close to factory spec, but weigh it again after you install the rings and tell me they are even close. Everyone may think I'm being too anal here, and that's fine, but my engine builds never fail unless I make a mistake by taking a shortcut. I use to take shortcuts when I was younger and it came back to bite me in the A@# alot. We should be encouraging this guy to do it right rather than telling him he can get by with doing it wrong only to have to possibly be tearing it apart again in the near future.

The piston "assembly" (rings and all) weight is the same no matter what the oversize. If you read my post you would know that these power heads come from the factory with different size pistons this includes the rebuilt power heads and the new engines. These are 2 stroke engines which are whole different ball game than 4 stroke. At the time I was doing this for a living (late 70's early 80's) life expectancy of a outboard was 1500 hours of operation this was usually only obtained by the commercial fisherman. power heads rebuilt in this manner or assembled new would last just as long as the the ones with all the same size pistons.

A complete teardown ? You betcha! But the need to make all the cylinders the same just isn't there, they won't vibrate and you'll never see the difference in a compression test

Here is something interesting. In 1977 Chrysler did not publish allowable piston to cylinder wall clearance in their manual. We had to badger them for 3 months before we got an answer and it was .020 thats right twenty thousandths.

 

[Frank Acampora]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Agree totally JFC. You and I know that when Chrysler and Force made these engines, they made 30,000 cranks and balanced the cheek weight to tolerances. Same with pistons--weight tolerance. They would not be caught dead rotating the whole assembly. Prohibitive cost. I have measured a whole bunch of rods and they are usually within 7 grams total weight difference--that's a lot, about 1/4 ounce. NO! I'm not a drug dealer--I just had access to a gram scale in a food lab.

We are not talking about a full out blueprinted race engine where tolerances are critical. We are talking about a relatively unsophisticated, low cost, nuts and bolts, low compression engine. And as far as unsophisticated, I once bought an engine that had never been torn down- I forget why I took it apart, but I found one of the crank pins had come from the factory with a big rough spot that factory machining of the casting did not clean up. Rough spot was on top of the pin right where the bearing rides and was about 1/8 wide by 1/4 long--and the engine ran quite happily with it no damage to rollers or rod bearing surface.. Needless to say, I did not re-use that crank though.

As I have stated before, I don't like to replace only one or two pistons because it offends my sensibilities. But if money was tight, I would do it with no qualms. And we both also know that some people boating really are on a tight budget and a few hundred dollars will make a big difference to them. If it's a question of repairing the engine "correctly" or putting shoes on the baby, which one do you think will win?

 

[Nate3172]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

I don't believe we are really comparing apples to apples here. Companies that remanufacture engines as a business and even the manufacturer itself will produce products that will last as long as the warranty will cover and still maintain low production cost. With that being said, they don't care so much if it is done right rather than can it last long enough to get past the warranty period. Now, if this guy wants to purchase a reman. power head than he can do so and obtain a warranty. We're talking about a guy who is looking to do this work himself and is not going to recieve a warranty for the money and time that he will put into it. You guy's talk about the methods the manufacturer and the reman. outlets use as if they are common practice, which they are within in the business of mass production. But, in the realm of the do it yourselfer, who wants to do it right for reliability and longjevity because that will be his only warranty, it is not common practice to use those methods.

 

[JCF350]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

I don't believe we are really comparing apples to apples here. Companies that remanufacture engines as a business and even the manufacturer itself will produce products that will last as long as the warranty will cover and still maintain low production cost. With that being said, they don't care so much if it is done right rather than can it last long enough to get past the warranty period. Now, if this guy wants to purchase a reman. power head than he can do so and obtain a warranty. We're talking about a guy who is looking to do this work himself and is not going to recieve a warranty for the money and time that he will put into it. You guy's talk about the methods the manufacturer and the reman. outlets use as if they are common practice, which they are within in the business of mass production. But, in the realm of the do it yourselfer, who wants to do it right for reliability and longjevity because that will be his only warranty, it is not common practice to use those methods.

Okay, the methods being discussed will last just as long as any other method. When I quoted life expectancy I meant just that, it is about 1500 hrs no matter how you do it, whether you throw in one piston or all of them. You do realize that you cannot turn a crank on these engines don't you? The hardened surface is too thin to even grind, which is why the roller bearings only come in one size. When rebuilding, checking the crank means a visual inspection and doesn't involve a micrometer? Going fast with these engines means you assemble it as loose as possible especially the pistons, reliability means you assemble it just a little bit tighter.

 

[Nate3172]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Maybe I'm a bit of a perfectionist and overly anal. On the other hand I think that is why I have return customers and they are allways more than happy with the work that I've done for them. I'm not just talking about race car engines here as that experience was just for reference, but I am that meticulous with every engine build I do. Does not matter even if it is a weed eater engine. I started rebuilding commercial truck engines in my grandfather's shop at the age of 12 and the methods that I have been taught do not include the ones you propose as being viable. If anyone has success with those methods than more power to them, but they are definately not ones I would ever endorse nor encourage.

 

[Frank Acampora]

Re: Cylinder #4 is toast.... please help diagnose (w/ pics)

Nate: we are not saying your method of rebuilding is wrong. All we are saying is that replacing one piston in a multiple piston outboard engine is acceptable primarily because factory tolerances are loose. And this guy just wants to get his engine running like it did from the factory. He is not looking for a race engine. Note that in a previous post I told him its the same amount of work to replace all four pistons as one, and if an extra couple of hundred won't hurt him, then he should do it.

Mind you--I repeat--I do not like to do it, but if a person is really tight for money and it makes the difference between repair and not repairing--Then-- Shoes and formula for the baby is always going to win.

It's OK to say save up money and do it right---but some people just won't have that option. Not too long ago I was one--lived paycheck to paycheck. Didn't know how I got the money to pay bills. That's why I started rebuilding my own outboards--If I wanted to go boating, I had to! And the first one I did was a three cylinder Chrysler with a melted center cylinder. Not only did it have a bigger piston, but it had 2 rings where the others had 3. Still runs quite happily with many hours of water skiing and cruising on it.

Would I do this now on a customer's engine? Not on your life! I would try my damndest to persuade him/her to replace all pistons. But if they insisted--I would accede to their wishes.