I have a #2 cylinder down with zero compression. All other cylinders are right at 100lb. I am going to scope the cylinder this afternoon. What should I be looking for? Boat was running great with brand new plugs on this run until #2 went down.
I have a #2 cylinder down with zero compression. All other cylinders are right at 100lb. I am going to scope the cylinder this afternoon. What should I be looking for? Boat was running great with brand new plugs on this run until #2 went down.
2006 Ranger Z20 Comanche
90% of the time it is number 2. Number 2 takes a number 2. They run great until they don't.
I suspect you will find chunks of the piston missing from top of the piston. Something like this probably.
Can we see some photos of the piston? Would like to see what the locating ring looks like if and when the piston gets removed.
By the way, what brand of oil were you using? What grade (octane) of gasoline?
Always yamalube and I just run 87 octane. This is a Jasper powerhead the previous owner had put on. According to him it didn't even have 100 hours on it. We have had the boat about 5 years with very little hours put on it. Does the 100lbs pressure on the other cylinders mean it's about worn out?
2006 Ranger Z20 Comanche
100 psi is not abnormal on a two smoke motor. They run low compression ratios. Minimum spec from Yamaha is about 80 psi. You are well above that.
There is just something funny about number 2 that causes it to fail moreso than the others. I suspect temperature but...
Yes.. photo… You may want to also scope #1. End of 2016 I lost my #2 and part of the piston shot over to #1.. guess since they share a port. No damage done to it but instead of cleaning and scoring, I just had the tech replace #1 as well for an extra $300 while he was in there…
In regards to the compression, I would think it should be above 100 for a new head with 100 hours on it. I mean my motor from 2006 has from 110-115 compression across all cylinders. 110 in #1 and #2 that I had rebuilt, which is a little confusing to me. I would think since it’s all new it should be nice and tight but guess other components are worn out. As long as you are within 5 or so of all cylinders compression wise, you should be good from that they say.
#2 is more prone to detonation. Higher temp is my guess also. It will also rattle the ring locating pins out causing the ring to spin and jam in a port. You need to run premium in these big block hpdi engines, 87 is running them on the edge, with proof from all of them destroying the piston. They also need to be proped to run the high end almost to the limiter and not lugged. Compression reading low across the board, gage reading low? As far as the 2 rebuilt cylinders reading low, run it for a while as they break in the compression comes up. Pistons could be different also. Cj
2002 X19 200HP OX66 HO Vmax,HPDI lower, it lives, thanks Hydro Tec.
Got a few pics from a camera we put down the cylinder. You can actually see the ring bent out.
2006 Ranger Z20 Comanche
When the piston disintegrates due to detonation the ring is susceptible to snagging.
Talked to a guy that rebuilds a lot of these motors. He says the yamaha pistons are crap. Once you get away from those your usually in good shape after that.
2006 Ranger Z20 Comanche
While I agree that there may be better aftermarket pistons that are available for the big block HPDI's, I don't think that the problem originates with the piston. In probably 95% or more of the HPDI big blocks, the original Yamaha pistons survive just fine.Originally Posted by Bumrush
What I am suggesting is that perhaps more than just a change in pistons could prove to be beneficial.
On my last boat a few years ago i had a 225 HPDI that had #2 go. I repowered with a 250 and splurged on a phase 3. Now running that required that i used Premium but i'm curious as to the reason for running it in a regular unmodded engine?
Current: 2006 ~ 20i ~ 250 HPDI ~ T1-25p
Previous: 2005 ~ ZX 225 ~ 250 HPDI Phase III - TXP 26p
The HPDI does not use a knock (detonation) sensor. Big block HPDI's seem somewhat susceptible to detonation. Usually in the #2 cylinder.
The purpose of octane is to prevent detonation. The higher the octane rating of gasoline the more it prevents detonation. The use of greater than the minimum octane rating in the big block HPDI (91/93 versus 87) is a form of insurance. Insurance against damaging detonation. It is cheap insurance in the scheme of things.
As noted, there are other things an operator can do to protect himself from detonation. Proper propping prevents detonation. Prop so as to reach red line RPM when the boat is loaded, in the middle of summer when the temperature is at its highest. Come up on the throttle smoothly and gently. Don't go hammering down on the throttle.
What is the max rpm for a 225 hpdi?
2006 Ranger Z20 Comanche
5500 RPM.
I'm just not much of a mechanic. Especially when it comes to a 2 stroke. So if I were to turn say 5600 to 5700 would that be detrimental?
2006 Ranger Z20 Comanche
you are good to 6000 . Take it to Hydrotech to get it rebuilt right!!! Full 1 year warranty.
Propping to 5600/5700 would certainly be beneficial from a detonation prevention stand point. That and the use of gasoline with a higher octane rating.
The longevity/life of the motor could possibly be diminished over time but it might not even be measurable.
Take it to hydrotech.
Going with JTM outboards. He has a great reputation and is only 2 hours away.
2006 Ranger Z20 Comanche
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