2 seized engines, need help with jetting.

afraz1er

afraz1er

Location
native idahoan
Just saw this at the gas station last weekend off Federal way. Stopped and took a couple pics of it. If you need some help with this send me a pm.

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ClassVgear

Location
Boise, Idaho
afraz1er said:
Just saw this at the gas station last weekend off Federal way. Stopped and took a couple pics of it. If you need some help with this send me a pm.

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Cool, Thank you for the offer. I may take you up on it. Currently I'm waiting on another set of pistons. They should be here by the end of next week. Thanks again

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ClassVgear

Location
Boise, Idaho
ClassVgear said:
Magnum Mike said:
listen to Augustaf and verify your octane vs dome cc's and bore diameter with RIVA. mention your use case too: big hull that has lots of surface area in contact with water. Since you have been through this twice already maybe go back to stock compression until all other issues are ironed out.

The pic of the 82.75 shows 1 corner, is there scoring on the other 3 corners? If you can post pics of both pistons in the the 82.75 and 83 sets. Show all sides and the tops of all 4 pistons.

Good reading material here http://www.groupk.com/tec-seizures.htm and here http://www.groupk.com/tec-rearseize.htm

going 40:1 and dual cooling will not solve the root issue but will give you more margin for error. Groupk recommended 40:1 when a 701 was in the waverunner 2 hull http://www.groupk.com/y753b2.htm GroupK also recommend 40:1 when a 650sx that was 50:1 stock is modified, 32:1 when a Factory Pipe is added http://www.groupk.com/restof650k.htm . I have not ridden with anyone running a modified engine with less oil than 40:1. Maybe they are out there but 40:1 is much more common.
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Thanks Mike, at this point I don't have any other option than to try stock compression or race fuel. Just seized another piston! . Just got off the phone with Riva and they say I'm good at 93 octane. My region only has 91. Most likely that's the the issue. Since intake side seizures is always lubrication failure, as far as I understand. Ill post pics as soon as I get them out. Thanks again

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I miss spoke about my fuel mixture. I mix 4 ounces oil to 1 gallon of fuel. I was using yamalube, switched to red line. I plumbed another cooling line and replaced all fuel lines. 170 main jet, 130 pilot, 2.3 n/s 95 gram spring, 20 psi pop off (verified 5 times). Switching to 37cc domes with an 82mm bore. Should equal 170 on compression. Anyone know what to expect with elevation gain and compression drop. I'm at 4000' above sea level.

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V

Vortex

Location
Southeast
50:1 is about 12 oz per 5 gallons so you are running plenty of oil.

I have no experience running at high altitude but from others that I trust, don't try to up compression to gain back lost power. I would run a slightly lower pitched prop or a bit larger nozzle. Adding more psi thru the motor will not change the fact that the air has significantly less o2 at altitude. It will still be struggling to breathe. Reliability>power unless money and time are no object.


Also what cdi are you running? Need to know if it's a 61x or 62t. You probably need the 62t
Less timing at high rpm.
 
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ClassVgear

Location
Boise, Idaho
Vortex said:
50:1 is about 12 oz per 5 gallons so you are running plenty of oil.

I have no experience running at high altitude but from others that I trust, don't try to up compression to gain back lost power. I would run a slightly lower pitched prop or a bit larger nozzle. Adding more psi thru the motor will not change the fact that the air has significantly less o2 at altitude. It will still be struggling to breathe. Reliability>power unless money and time are no object.
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I'm dropping compression. Was running 35cc domes 180psi. Dropping to 37cc 170psi. I know altitude and temp play a huge factor, I just don't know how much.

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V

Vortex

Location
Southeast
37s should help. I'm sorting thru the same issue on my ski. Have 83mm pistons and need domes that will lower compression to a safe level. Might even have to get 760 domes. On some motors going up 1mm larger piston increases psi readings by about 10-15psi. I used to run 33cc domes on 82-82.5 bore and I'd get 210psi.

Also cranking psi does not tell the whole story. Even at 37cc it would not hurt to mix maybe one gallon of 100+ octane per 5 gallons. You would have to calculate dynamic compression mathematically to know exactly what is happening.
 
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ClassVgear

Location
Boise, Idaho
Vortex said:
37s should help. I'm sorting thru the same issue on my ski. Have 83mm pistons and need domes that will lower compression to a safe level. Might even have to get 760 domes. On some motors going up 1mm larger piston increases psi readings by about 10-15psi. I used to run 33cc domes on 82-82.5 bore and I'd get 210psi.

Also cranking psi does not tell the whole story. Even at 37cc it would not hurt to mix maybe one gallon of 100+ octane per 5 gallons. You would have to calculate dynamic compression mathematically to know exactly what is happening.
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Just did the math on mixing fuels. 1 gallon of 110 to 4 gallons 91= 94.8 octane. That should be good! Brian at Riva told me that in order to run 91 octane pump gas I need 37cc domes with 83mm pistons. Currently I have 82mm pistons with 35cc domes. So with 37cc domes and 94 octane mixed with red line at 40:1, I shouldn't have the same issue?

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V

Vortex

Location
Southeast
The changes to your fuel/oil and cyl head will help but you can still absolutely seize an engine with no signs of detonation.

A 61x cdi has 22 ish advance at 6500+
A 62t cdi has 18 at 6500+

Earlier timing at high rpm=more heat.

I would do whatever you need to do to have dual cooling outlets from the head and keep a reaaaal close eye on engine temp. If it's getting close to 150+ that's a slight cause for concern. Need temp strips on both cyl and the exh chamber

And your jetting needs to allow smooth metering across the various fuel delivery circuits in the sbn. (Obviously)
 
long beach local

long beach local

long beach local
Location
Az
holjen77 said:
If the other piston dome is clean check exhaust manifold for warpage which can let cooling water into chamber.
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I had this problem on a ported 760. kept melting the rear piston on the intake side drove me nuts , jetting, detonation etc. finally figured it out to be a leaking exhaust manifold to cylinder as the 8mm time certs were stripped and pulling out. I sent pictures to Tim at TNT of top of the pistons and he said i was leaking water somewhere, Your one picture of the top looks abit like mine did.
 
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ClassVgear

Location
Boise, Idaho
x2mafia said:
You try throwing more water at it yet?
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Have both cooling ports running. Seizure on intake side always means lubrication failure. The fuel I was running turned out to have ethanol= death of 2 stoke. Have confirmed ethanol free fuel now and red line oil. Will be testing again next week.

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x2mafia

x2mafia

Maximum effort
Location
WA
That doesn’t mean anything since You have a jetski engine in a raft boat thing. And it’s just a 61x with a b pipe and a head lol.

Btw I run Safeway gas in my tpe and she rans reeel good. Your overthinking this whole thing lol
 
x2mafia

x2mafia

Maximum effort
Location
WA
but Hey what do I know I’ve never built a raft boat before. Probably check squish again and uh static timing @30 degrees past boost port opening and totally overlook the obvious
 
Jhucke

Jhucke

Location
Wisconsin
ClassVgear said:
x2mafia said:
You try throwing more water at it yet?
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Have both cooling ports running. Seizure on intake side always means lubrication failure. The fuel I was running turned out to have ethanol= death of 2 stoke. Have confirmed ethanol free fuel now and red line oil. Will be testing again next week.

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When does it seize? Full throttle or somewhere in between? It’s not ridiculous to think that your carb settings are off mid-throttle causing a lean condition. I know someone that stuck a piston cruising for awhile. Like that point when you’re on the pipe and off the pipe throttle range. The huge raft thing probably screws with it, too.
 
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