1990 ( 90 hp v4 ) compreasion readings

[StingRay_90V4]

I checked my compression of my 90 horse v4 this weekend. I wanted to get some thoughts on my numbers and the overall health of the engine.

1. 138 ish ( almost 140. But not kwight )
2. 135
3. 135
4. 124 ish... ( it was just a hair below 125 )

Are these numbers good ? I was fairly impressed honestly. My old 86 rude 60 hp runs compression of 105 psi on one cylinder and 122 ish on the other 2. and runs excellent. And honestly i was even happy with the 90 v4s lowest cylinder of just a hair over 125. So maybe 126 or 127ish. It wasnt kwight 130. They all seem good to me and make me feel as though my engine has many good hours to go yet. But i wanted some of your thoughts on the numbers?

 

[Baylinerchuck]

I agree with you, those are pretty good numbers.

 

[StingRay_90V4]

I thought so too... But i just wanted to hear peoples thoughts about a low of 124 ish and a high of 138 ish.

 

[StingRay_90V4]

Anyone else ? Lol...

 

[interalian]

Well, the 124 is about 10% down from the others, which is usually regarded as within tolerance. What's your model number?

 

[StingRay_90V4]

It is Ve90tlesb


And the 124 ish may have just as easily been 125 and the higer 138 ish may have just as easily been 137 . making them even closer. It was kinda hard to read the in between numbers.

 

[StingRay_90V4]

I guess what im really wondering is if everyone else would be happy woth those numbers or would they tear it apart and rebuild it.

 

[racerone]

More inspection can be done.----Find the bypass cover with 6 small bolts.----Remove it to look at the side of the low compression piston.--Will cost you a $2 gasket to learn about this motor.

 

[StingRay_90V4]

What specifically would i be looking for if i did that ? I was mostly hoping that my compression numbers are all considered to be very good. They are within the magic 10 to 12 percent for sure that everyone has told me to look for. A few boat shops even told me 15 percent is do-able. I would hate to rebuild it when even the low compression cylinder is 125 ish. Maybe if i recheck it and crank it over a second time for a second it may hop up to 130 psi.

 

[racerone]

I for one do not think that everything is A OK with that motor.------But it is your choice.---Broken rings are so common on these motors and easy to inspect for that.

 

[StingRay_90V4]

Im surprised to hear you say that you dont feel that the numbers are not good ? I may try to de carb the cylinder. Maybe that cylinder has a slightly stuck ring and a good sea foam in the cylider and in the gas tank for a bit may bring it up as much as 5 psi. Which would then be 130+ psi. My friend that was there with me is tellimg me he thinks the gauage read 125 psi and that he cranked it the shortest of all cylinders. At the end of the day the high cylinder is 135+ and the low cylinder is 125. Well within the 10 to 12 percent . why would u think its not in good shape ?

 

[racerone]

Every one of these motors will end up on the work bench with broken rings.---That is just the simple fact that some folks refuse to believe !

 

[StingRay_90V4]

Oh im not saying i dont believe that they break rings at some piont. But in my 30 years of workong on engines. More cars then marine applications. My experience has taught me that I do not have a broken ring at this piont. Nor do i beleive that a broken ring can or will produce compression near 125+ psi. I only asked this question here origanally to get some advice on my numbers from people that have worked on these older v4s. Which... I know drom lurking on here for quite some time and reading a lot that you happen to be one of them. However... I question your train of thought as to weather or not my rings may or may not be broken. As well... Im surprised you didnt mention to first try and decarbon the engine and then re check its compression. I get that a lot of them will break over time. But i dont think i am there yet. I bet after a de carbon treatment that 125 will turn into at least a 130 if not 135. I would expect a broken ring to be in the low low 100's. Say a 105 or 95 or even 90 or less psi. Not a still strong 125 psi and maybe more. There are more then on reasons for low compression. Such as stuck rings due to carbon. Or in some cases if 2 cyl are down. A blown head gasket. Or even just plain old hours and wear and tear. I can still fly out of the whole and do 40 mph all day. It will climb to a absolute top speed of 41mph. I have seen 42 mph a few times with just myself in the boat. Could a broken ring still perform that well ?? Seriously... Im curious...

 

[racerone]

I am not going to argue this subject of ring failures on these crossflow motors.---------Got a barnfull that need to be rebuilt.-----Good luck with yours.

 

[Fed]

What causes them to break racerone and is there anything a user can do to minimise the chances of breakage?
Overprop, underprop, overheat, better oil, don't flog it etc?

 

[interalian]

As a point of reference, I recently rebuilt one of these using a donor '79 140hp block and combined parts with a low hour '82 90hp - our original family boat/motor purchased new in '83.

The '79 donor motor had suffered a broken ring on #1 causing catastrophic failure of that piston when the ring fragments hooked the exhaust port. #3 also had a broken ring but it hadn't caused damage in that hole. It was the top ring, and the break was at last ~3/4" near the gap, toward the exhaust side. Despite this, poking the ring from the bypass port showed good/similar tension to those on #2 and #4 which were both in good shape. This donor most likely failed due to swolen/displaced diverter rubbers on the 1/3 bank, and #3 was likely close behind #1 for failure. All pistons were horribly scuffed and all bores deeply scored. Water pump was also burned up.

The '82 motor had never been apart for any reason and showed all bores with factory crosshatch still visible, no scuffed pistons, and no broken or stuck rings despite its age. This 90 horse motor (flywheel rated for power) only had 90/95 pounds on one bank and 100/105 on the other. Some variance between banks is generally accepted as a function of block machining between sides.

You have one bank with equal and high compression, and the other with a high and a low. Does this mean you have a broken ring on #4? I don't know, but if racer suspects a problem, I'd be inclined to dig deeper. Heck, if I knew where he lived I'd by him a couple of beers for the help I got on my job.

 

[racerone]

Simple---Draw a picture of the top ring in the groove.---Then see that as the piston wears and the ring wears the side clearance increases.----At 5000 RPM the ring will bounce and eventually break.--Ever notice how much slop there is on a crossflow piston when cold !!!!

 

[StingRay_90V4]

I guess to be honest at this right now im not to worried about it at this piont. My father claims after talking to him an hour ago he went out and checked them all again him self after having the boat out for awhile. He says all 4 are at 135. Even... Period. So idk... Maybe my gauge isnt that great. Or maybe i forgot to hold the throttle wide open on the last one. I cant remember. Perhaps i will just drive her until she stops performing at all. I can tell you it out does our 60 hp evinrude of the same year in all areas. Except gas conservation. If and whem the time comes i will rebiuld it myself. Or look into a newer Etec 90 H.O. after rebuilding our 60 uears ago im sure the 90 wont be too mich harder. The 60 was dead easy.

And as for the slop on a cross flow piston. I have never had one apart yet. But mechanics 101 tells me to not flog any machine cold. Always let them warm up. An engines tolerances will always tighten up as it reaches operatong temps. I sure hope no one ever starts any engine and goes straight to wot at 5000+ rpm. Thats also another way to use an engine for a boat anchor. That was probably the first thing they taught us in my mechanics class 20 years ago.