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  1. #1

    GP1800/SVHO Head Cracks

    HI Guys,

    There is a few threads on this already but Yamaha have inspired me to consolidate the issue and make sure that the wider community is aware that the SVHO engine has a confirmed issue with head cracking.
    The more data we collect the better the jetski community will benefit and the collective knowledge may help find a solutions to the issue because Yamaha certainly do not want to know about it or help. anymore*

    My 2017 GP1800 has the following items fitted




    • Worxs ride plate

    • Worxs sponsons

    • Worxs air intake pod filter

    • Worxs steering column

    • Worxs 8650rpm tune but it sits around 8300 rpm with the prop pitch

    • Worxs extra cooling line

    • Worxs blow off Valve

    • Riva intake grate

    • Solas 13/18 prop
    • R&D SC shaft

    • Titanium valve retainers





    This was the perfect ski for the first 54 hours!

    I was cleaning the ski after a ride one day when I noticed a thin film of oil in the bilge, I thought it could of been caused by some spillage after the last service so I cleaned it out and made a note to monitor it next time I rode it.
    Sure enough, about 10 mins into riding it the next time I stopped and removed the seat to inspect the bilge for oil and I could faintly see a thin film of oil in the bilge.
    I continued riding thinking that it could be oil left over that I didn't get when I cleaned it last, when I stopped after about an hour there was noticeably more oil than before in the bilge.

    This is the point where I went, nahhh it a Yamaha, I bought a Yamaha because I didnt want to have maintenance issues.

    After cleaning the whole engine bay with brake cleaner and removing all traces of oil, I started it up on the hose and started looking for oil leaks.
    It wasnt long before I saw a small stream flowing from under the oil tensioner feed top banjo fitting.
    I replaced the washers on the banjo fitting even though It didn't look like it was coming from there and tried again, the oil was still leaking. On a closer inspection it looked like it was coming from "no where" and the sad truth was faced.
    The head was cracked!

    During fault finding the cylinder compression was recorded and all 4 pots were sitting at around 145-148 psi

    The dealer wasn't overly surprised when I said the head was cracked as they explained they had just went through this process with a FX and I joked I must be lucky to have got a head from the same batch.
    The dealer approved warranty and a month or so later I had my ski back with a new head.
    When I picked the ski up the Idle was "rough" and even the mechanic agreed and said the cylinder PSI had changed "slightly" and put it down to valves not being run in yet..

    I spent the next day riding it and to my delight no oil in the bilge, but the idle was still rough, I though surely these valves had run in by now!?

    I had not rode the ski since the last time and I had a race round coming up so I was keen to make sure the ski wasn't going to break, so I set up some buoys and did some training. The clutch went on me, I was bummed but also kinda happy that it had gone then and not during the race.

    I was lucky enough to find a clutch in 7 days and have it fitted.
    (note: I didn't bother claiming warranty as running extra RPM's will reduce clutch life, you except it so its not so bad when it happens)

    Race round came and went (winning all 3 motos) This ski is fast!

    Still it was running rough at Idle.

    The cylinder compression was tested and 3 of the 4 cylinders were still down, one as low as 135psi!
    The rocker cover was removed to check the lashings/ valve clearances and this is where things get interesting.

    Something missing




    Something found


    The welsh plug as you can see was missing from the exhaust cam, WTF is going is on?
    I was planning on fitting titanium retainers so the cams where coming off any ways, so we fitted a new welsh plug once we took the cam off but we were still scratching our heads.. this is a Yamaha after all!

    Next step was to check the valve clearances, WOW! two valves where out by 0.05mm and one was out by 0.1mm, we had found the lost compression and rough idle culprit.

    (Look this was maybe a point to tell the dealer they stuffed up but meh.. my ski was going to be back to normal and thats all I cared for.)

    Installing the retainers




    Every thing was re-assembled the cylinder compression was tested (back to 145-148psi across all 4)
    Started her up and it sounded like it should again, YAY!


    The ski now has 60 hours on it and its a week out before the next race meet, I was doing some rec riding in the ocean, jumping waves and all that fun stuff When I noticed oil again in the bilge.
    I automatically start looking for a loose line, leaking gasket purposely avoiding looking in the same spot that the last head had cracked.
    I didn't want to accept that the head could crack again, only after 6 hours use since the new head was installed!

    The head had cracked again in the same SPOT!
    I actively said F*&k it and raced, I literally just topped the oil up through out the day, the leak was slow, I lost maybe 100ml for the day. (was worth it kinda with another clean sweep for the day, I should note I am the only one who has a GP1800)

    Back to Yamaha..
    Mind you If I though I was causing the head to crack I wouldn't be a dik and go sooking back to Yamaha crying that my ski had broke again. But I did think that I might be the culprit so I called others and asked, have you had this issue?
    after speaking to blokes running turbo kits and spinning the engine at 10,000rpms+ and them not cracking heads, I was like nope I cant be!


    Warranty denied!
    Warranty denied!
    Warranty denied!

    Yamaha Australia will not warrant a cracked head if you flash the ECU and spin it at more than stock 7400rpm
    Spinning a SVHO engine above 7400rpms will cause the head to crack as per below!

    The first head was done under good faith as I have "highly modified the engine"


    Where to from here, What extra info have I found out, What have dealers told me!?

    My favorite so far from the dealer and I Quote "the extra oil cant drain fast enough and thats why its cracking"

    When dealing with Yamaha be prepared to be lied to!

    After my local dealer had denied warranty I called Yamaha motors head office here in Australia and spoke with "John Citizen" the Tech support officer.

    I started the phone conversation off with- Hello John Citizen I have a GP1800 and the head is cracked and my dealership has denied the warranty on it.
    JC-Thats no good at all explain to me every thing so I know whats going on, what work have you done to it?
    Me- I went to tell him the story (I explained the above work.)
    JC- Well because you have flashed it, its not covered under warranty!
    Me- Explain to me how the head can crack twice in the same spot and the flash is the cause!?
    JC- Dosnt matter its been flashed
    Me- Mate, just because its been flashed it dosnt explain how the oil pressure is getting so high to blow a hole in the casting and punch the cam welch plug out..
    Me- have you ever seen this before?
    JC- no I havent seen or heard of this problem before.

    Tug-o-war continues and gets more aggressive for the next 5 mins

    Me- The dealer told me the Yamaha race team have been having this issue and they have spent a lot of time and R&D to fix it
    JC- Yes i told them that..
    Me- You f&%& what! you just told me you knew nothing about this issue and yet you just admitted you have known about my case and this issue the whole time,

    I called him a nice person and hung-up

    Basically once they say no, give up, its easier!
    But I also recommend having a friend with a stock ski.. thats all I am going to say.

    Whats causing this issues and what am I going to do next?

    Theory 1
    The heads Yamaha are getting made atm are shit and have a lower pressure rating than previous batches
    (I have been told other model Yamaha heads are cracking too)

    Theory 2
    The oil pump assembly is the cause. I only say this because how else can the pressure build up so much that the welsh plug gets blown out of the cam and then obviously the head cracking.
    Is the oil pressure regulator failing/ not releasing well enough, the first head lasted 54 hours and the second only 6 hours, this kinda points that something else is going on.

    Theory 3
    a mix of the first two theory's

    In the mean time-

    I am going to fit a second hand head from a SHO that is from an era where this issue did not exist and when I pull off the oil pump assembly I am going examine it to see if any thing looks out of place/degraded, mainly the oil pressure regulator and spring.

    -Luke


  2. #2
    I would send ur old svho head to jim.

  3. #3
    MSX 150 guy lives on Mr. GP1800's Avatar
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    Quote Originally Posted by seabrook View Post
    I would send ur old svho head to jim.

    You are saying that people can repair these? That sounds like an ideal solution

  4. #4
    Click avatar for tech links/info K447's Avatar
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    Yamaha Australia will not warrant a cracked head if you flash the ECU and spin it at more than stock 7400rpm

    Spinning a SVHO engine above 7400rpms will cause the head to crack as per below
    What RPM level is the stock ECU rev limiter set at?

    Worx 8650rpm tune but it sits around 8300 rpm with the prop pitch
    It seems that there are many SVHO engines running tunes revving into the 8300-8500 range. I have seen a few threads reporting cracked SVHO cylinder heads, but overall not that many.

    Was the original cracked head ever removed from the engine prior to the first crack failure?

    Apparently the replacement cylinder head was installed by someone that may not have been careful, given the valve clearances you discovered. Perhaps some other aspects of the head install were not done correctly, setting the stage for the second head failure?

  5. #5
    Bernies10's Avatar
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    Mate this is my nightmare scenario too, 40 hours running 1 plus and so far so good. I know they don't all go but if this one does i'm out of thousands as theres no warranty here (imported from overseas)

  6. #6
    Quote Originally Posted by K447 View Post
    What RPM level is the stock ECU rev limiter set at?

    It seems that there are many SVHO engines running tunes revving into the 8300-8500 range. I have seen a few threads reporting cracked SVHO cylinder heads, but overall not that many.

    Was the original cracked head ever removed from the engine prior to the first crack failure?

    Apparently the replacement cylinder head was installed by someone that may not have been careful, given the valve clearances you discovered. Perhaps some other aspects of the head install were not done correctly, setting the stage for the second head failure?
    Hey Mate,

    The original head was never touched or removed up until the 54 hour point.
    The location of the crack is isolated from stress points associated with incorrect torquing down of the head.
    If I had oil in the water then I would suspect that the head had been installed incorrect and would find cracks around bolt down points.

    The cracks have all been on the out side of the casing not near bolt down points.

    There is more out there with these issues than you would expect, The missing welsh plug is becoming a common thing from what I hear from others.

    Its actually scary because if the welsh plug blows out there is no way to know and if you are just sitting around at idle for extended amounts of time the risk of the oil not getting to the correct places on the cam and damage occurring is very real.

    We replaced the welsh plug with an after market one with the same OD but was about 3mm taller so there was more "bite".

  7. #7
    Quote Originally Posted by Mr. GP1800 View Post
    You are saying that people can repair these? That sounds like an ideal solution
    Yea magnum


  8. #8
    Quote Originally Posted by seabrook View Post
    Yea magnum
    I was aware that people have attempted to weld the cracks just end up chasing the cracks due to the material make up of the heads and how they react to extreme heat caused through welding.

    I could imagine it might be possible to drill out the crack and tap a plug but then you have the possibility of creating more weak points and affecting oil flow.

    Does Jim have a website/contact details?
    Is he across the coral and north pacific ocean? (Route from AUS to USA?)

  9. #9

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    I'd say blowing the cam plug out is definitely from the higher rpms/oil pressure. years back they/people used to regularly pop the plugs out and tap 1/4" allen plugs in there or spot weld the plugs in to prevent that.

    as far as the head cracking who knows. i cracked one. ran it 300hrs give or take with an rpm limiter of 9200 super charged no problems. went turbo and during tuning it right off the bat low boost (12psi) cracked the head for no apparent reason. cracked by the head bolt boss. fwiw jim told me run head studs so i did. probably got another 20ish hours since then, still tuning up to 18psi but no more cracks.

  10. #10
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by Luke1.8 View Post
    Hey Mate,

    The original head was never touched or removed up until the 54 hour point.
    The location of the crack is isolated from stress points associated with incorrect torquing down of the head.
    If I had oil in the water then I would suspect that the head had been installed incorrect and would find cracks around bolt down points.

    The cracks have all been on the out side of the casing not near bolt down points.

    There is more out there with these issues than you would expect, The missing welsh plug is becoming a common thing from what I hear from others.

    Its actually scary because if the welsh plug blows out there is no way to know and if you are just sitting around at idle for extended amounts of time the risk of the oil not getting to the correct places on the cam and damage occurring is very real.

    We replaced the welsh plug with an after market one with the same OD but was about 3mm taller so there was more "bite".
    Where exactly on the head(s) are the cracks occurring? One particular spot or multiple?

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