Rebuilding 300 HPDI

[matise46]

I have a 2005 300 HPDI that had a problem on # 2 cylinder at about 190 hours and was replaced under warranty with whatever updates they do. It ran fine until about another 190 hours when the #2 cylinder went down again. Going to rebuild and try it again . Is there anything I can do to make this a more reliable motor while I’m in it ? Thanks for any advice.

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[87gtNOS]

I am in the process now...mine just had stuck rings that lead to some wall damage...

waiting on the new pistons...

http://www.bbcboards.net/showthread.php?t=1072451

[matise46]

What brand pistons did you go with?

[87gtNOS]

WSM

[CJ1]

WSM pistons, prop to just under the limiter, premium fuel non ethanol if it sits for over a few weeks, Injectors cleaned and flow tested with the higher flow rates in the upper cylinders #2 especially. CJ

[87gtNOS]

Which is #2....portside middle?

[jdwo2212]

Yes.

[87gtNOS]

Why do they drop #2?
Mine had pinched rings in #2. No compression. Exhaust side scored. Top of piston was normal and plug and head too.
Had injectors done and #5 was bad. So I bought one new Yamaha injector and it will go in #2...

[CJ1]

Why do they drop #2?
Mine had pinched rings in #2. No compression. Exhaust side scored. Top of piston was normal and plug and head too.
Had injectors done and #5 was bad. So I bought one new Yamaha injector and it will go in #2...

My guess is that cylinder runs a little warmer because of waterflow, porting, or whatever. So that would be the first one to start detonating. With the stock pistons it rattles the ring locating pins out or destroys the top of the piston. We have 2 300HPDI engines, both on original powerheads. Both are propped to the limiter. One has meticulous maintenance. The other, not so much. Waiting for that one to fail but it hasn't happened yet. I truly believe lugging them and poor fuel it 90% of these engines issues. What was Yamaha thinking not putting a detonation sensor in these lean running engines???!!! Must be the same Igitneer that has written the SHO break in procedure. CJ

[87gtNOS]

funny, mine had 20 over WSM pistons....it will all now be 30 over WSM pistons!

[CJ1]

funny, mine had 20 over WSM pistons....it will all now be 30 over WSM pistons!

The only thing WSM pistons stop is the ring locating pins from rattling out. They do not stop the detonation from taking chunks of the piston out or collapsing the top of the piston into the ring land. this is akin to hitting the top of the piston with a hammer on the way up. what fuel do you run? do you have modded heads? are you propped to 6k without overtrimming? Injectors been cleaned? Normally there is a cause and unfortunately for some the case was not fixed and they experience a failure immediately after the rebuild. CJ

[87gtNOS]

The only thing WSM pistons stop is the ring locating pins from rattling out. They do not stop the detonation from taking chunks of the piston out or collapsing the top of the piston into the ring land. this is akin to hitting the top of the piston with a hammer on the way up. what fuel do you run? do you have modded heads? are you propped to 6k without overtrimming? Injectors been cleaned? Normally there is a cause and unfortunately for some the case was not fixed and they experience a failure immediately after the rebuild. CJ

Stock heads, 91 octane, seafoam, that injector was good (#5 was not so good though) 6000 rpm or so, fully trimmed though up, 1.5" below the pad.....
So now 5 good injectors (cleaned, flowed) and one NEW yamaha injector (will put the new one in #2). New tstats, but old ones seem fine as the hot water comes to a boil in a pot...poppet valve was screwed, might have been sideways in it's seat...put in a new pne.
ALL mystery filters done last summer, ALL.

[skeeter21i]

Which is #2....portside middle?

i believe port is 2 4 and 6 and 2 would be the top 4 the middle 6 on the bottom starboard is 1 3 and 5 1 on top 3 middle 5 bottom

[jdwo2212]

i believe port is 2 4 and 6 and 2 would be the top 4 the middle 6 on the bottom starboard is 1 3 and 5 1 on top 3 middle 5 bottom

You are correct. I read it wrong and was quickly corrected by a friend. :) #2 top port.

[mercuryproxs77]

Wsm pistons +1, stake the locating pins, bore to .001 in over on all cylinders for extra tolerance, good clean fuel without ethonal if possible, Always run the octane rating your motor has been tuned for, run yamaha fuel treatments, change all the fuel filters and screens EVERY season, make sure all your fuel lines are clean and arent breaking down from the boat to the motor(you woulndnt believe how many times i find this to be where the sediment comes from in the system), prop to just under the limiter+1, keep the cooling system up to snuff, and always bring the engine up to temp before you jump on it and let the engine temp stabilize after hard run before you shut it off.

[87gtNOS]

so my 08 250 stuck the rings on #4......#2 was not far behind.

[CJ1]

so my 08 250 stuck the rings on #4......#2 was not far behind.

Hummm, what oil you running? Cj

[87gtNOS]

Amsoil

[87gtNOS]

Any benefit to turning oil lever up maybe the amount of one of line-up line on the lever?