Yamaha 300 HPDI Powerhead Rebuild: Diagnostics & Decisions

Part 2 of rebuilding this Yamaha hpdi 300 vmax 2 series outboard engine. It has blown a cylinder so we consider why and what to do next. 2 strokes are a dying breed but still greatly appreciated by many so we will make an effort to restore this fine example.
We are a small machine shop in western Massachusetts and this KZbin channel is a reflection of some of my day to day efforts and interests.

[@JhanDeCal]

I just rebuilt one myself. The HP fuel pump was clogged @ the "mystery" basket filter on the port side and I lost cylinders 2 and 4 due to lack of fuel and oil. I re sleeved the cylinders and swapped out the pistons with used ones. I did all the work with out removing the power head from the outboard while it was still on my boat. Back to 120psi on all 6 cylinders. 👍 Good luck with your rebuild. 👍

[@thegentleman1541]

This seems to be a VERY COMMON issue with the 300hp & 250hp HPDI. If you do a search you'll see thread after thread of Cylinder #2 Piston failures. Its crazy. Seems like a manufacturing defect to me. HPDI's are great engines.

[@bakervinci163]

I have a 2023 300r power head with less than 50 hours that a fake mercury mechanic took off my engine. He first tried to tell me it was not mine . What should I look for , as possible parts he might have taken off ? I am going to rebuild the head and sell it

[@REPENTINCHRIST]

Thank you for not saying "PRE-DETONATION" cause "detonation" IS "PRE-IGNITION"! So it is like saying pre- pre-ignition, but I hear it from mechanics all the time, you sir, are a technician!

[@chucknubern8549]

Where can I find the rest of the videos of the rebuild?

[@nevatotadat1905]

Great video! Are these Direct Fuel Injection motors?

[@Mroswaldo16]

That looks like it ran lean. I have 2 stroke ski & see this happen a lot from not enough fuel. my brother has a 250 vmaxx hpdi & we had gotten bad fuel from gas station & we ran into this problem. Until we swap fuel & all the filter & mystery filters, cleaned injectors. But his measured like 60psi.

[@maximodiaz1543]

Back in 2003 we had 2 brand new one of these 300 HPDI's and they both faced a similar failure to this after about 50 hours and they both did the same thing within 2 hours of each other. When we got it back to the Yamaha dealer the dealer told us that this happened due to the use of an oil that wasn't Yamalube (they had Penzoil), I don't know if that is true or not but we have only used Yamalube since and the engines have 1200 hours now with perfect compression on all cylinders.

[@bakervinci163]

There is no way that the types of oil would cause a catastrophic failure. I’m in the medical field and doctors and surgeons will say the same types of things .

[@aaronp005]

Where is part 3? Its been a month. I want to see you rebuild this!

[@robertkilgore4257]

Yes! I would like to see the re-sleeve part. Have been wondering if that would be something I could do to my 300 and then I see this video.

[@shopdreamin372]

Hello Aaron and Robert, I have been a little bit spread thin with my regular work lately and my next step is to pull the powerhead from the rest of the outboard and space is already tight. I will be making part 3 shortly as soon as I wrap up the few jobs I'm working on now. I appreciate you guys watching and do stay tuned

[@thomasm9177]

Rebuild with WSM pistons and get away from the factory Yamaha pistons.

[@kawasakirule3707]

DIY is always the best. Then you know it's done right. And U save TONS of labor costs.

[@dyronbaron2566]

Contact me I'm a fan of 2 stroke

[@hugomoratillo8453]

Thanks for your video. I have a 2003 Yamaha HDPI 250 HP with low compression in cyl 5 and 1200 hours. Is it worth it to rebuild this motor? I am finding out that parts are expensive. Thank you

[@shopdreamin372]

At 1200 hours you may need to have your block bored to the next piston size. If you are just having low compression and no catastrophic failure then you could potentially just get away with replacing the piston rings and probably the crank bearings since you would be in there. That would be the bare minimum job along with filters/gaskets

[@hugomoratillo8453]

@@shopdreamin372 Thank you

[@Bluebuyz]

Do you rebuild engines that are flooded

[@havocsquad1]

Nice, keep the outboard powerhead videos coming. Most are just carnage/disassembly videos or test videos after the rebuild. Just buttoned up the crankcase cover on my own OMC V4 90 degree crossflow two stroke outboard. It had stuck rings and end gap was at max spec on all pistons, so got new piston kits after the bores checked out to be within spec by a machine shop for std size bore and cylinder walls got de-glazed. Crankshaft bearings looked nice and moved quietly. I loath those OMC connecting rods, they are worse than doing my taxes. Troublesome buggers to align those rod caps. There were some days I wish I had a holographic OMC master tech on some questions that the OEM service manual and no one else really answered right/well.

[@shopdreamin372]

Thank you, stay tuned. I havent worked on it in a few days since it's a side project but I will be making another video shortly, i think the next step after a little bit more disassembly will be to pull the powerhead. I hope the rotating assembly goes smoothly since I'm just diving in here with no instructions really. I do know my engines fairly well but this will be the first "large" engine I'm working on. But goodluck, I hope your engine will be in top running order once it's all together.

[@antonioprado8068]

​@@shopdreamin372 how much did the motor cost before breakdown. How much total with the parts and how many hours of labor. Cause most don't have all the machinery like you

[@stevenferraro7896]

Rebuild

[@robertjackson7590]

The oil and gas aren't mixed on this engine. The oil is injected behind the butterflies. The gas is injected on the piston crown.

[@shopdreamin372]

Hmm that I did not know, I figured the gas and oil were mixed in the pump. Good information

[@robertjackson7590]

@@shopdreamin372 sarcasm I guess but your the one suggesting the oil and gas are mixed and they aren't in this engine at any time. Sorry if I offended, many others have said that same thing.

[@shopdreamin372]

@@robertjackson7590 not being sarcastic, I assumed they were mixed because it is a 2 stroke.

[@robertjackson7590]

@@shopdreamin372 cool, look up a company called Hydro Tec

[@dylanconrad6830]

How do you remove the sleeves?

[@shopdreamin372]

It will depend on the type of cylinder. Some we press out with an arbor press using a fixture that applies even force onto the sleeve. But some cylinders that come sleeved brandnew will have the aluminum cast around the cast iron cylinder sleeve so they have to be machined/bored out. In this case I think the one sleeve will be machined out as the block is really big.

[@adc-professionalunderwater7775]

What's the update on this rebuild?

[@francescopierre-nina9515]

Excellent video- just discovered my 200hpdi 2004 flywheel wont revolve so assuming its seized since last started 3 months ago when I changed mystery filters.. took off timing belt and tried to rotate crank shaft a bit with tbar on 36mm box spanner after spraying some two stroke oil and wd40 into cylinders (left overnight) but will not budge.. assuming there might have been water in fuel or moisture got in when changing the mystery filters- but it started and ran fine after that job- any ideas what to do before I start opening head? Tks v m