My (Daytona?) "Freeride" SuperJet Project

[Sanford]

60 minutes into my easy "break-in" ritual I was heading back to shore doing 15 or 20mph (3K to 4K rpm - constant speed for 200ft) then it gently (if there is such a thing) siezed. I say gently because after it seized it started up...but I only idled to shore. Tore top end down and my rear piston is toast.

The story is very odd however and many things just don't add up. I check compression and its 195psi on the front (good cyl) and 190 on the rear (seized cyl). The odd thing is I am using 35cc domes and should have a mathematical compression of 185psi...not 195psi.

It gets even more odd. I made the mistake of not double checking the new bore clearance (piston to cylinder wall)...in the rush I "assumed" the machine shop did their job. Turns out there is .065" piston clearance. While this is a little high, certainly not the cause of the siezure. If nothing else, it would/should have helped with the greater clearance...not caused it.

Carbs were jetted right (135/72.5) and screws were fat. Base gasket was mint. Cases sealed well.

I'm scared to re-bore it and throw new pistons in it because I didn't find anything really wrong.

The only 2 things really odd is the larger clearance cylinder and I'm using a Blowsion billet head (with 35cc domes - on non big-bore 61x).

I am so sick about this because it just doesn't make sense. If I found the problem during disassembly, I would rush to bore, new pistons and get this done....but without a clear reason...:banghead:

Ran fantastic for the first 59 minutes.

 

[WaveDemon]

did you check your squish?

 

[Mark44]

What was you squish? Did you pressure test the motor before you put it in?

Mark44

 

[Sanford]

The other odd thing is my squish is .052" and not under the critical .040"

 

[WaveDemon]

what brand piston did you use? did you check your ring end gap?

I bet it's not an assembly error. I'd look real hard at the carbs. group k has an article on partial throttle siezure. I remember that it said something about being at the torque peak and some carbs don't handle that situation well.

 

[WaveDemon]

seizure articles:
http://groupk.com/tec-seizures.htm
http://groupk.com/tec-rearseize.htm

the break in seizure looks like it's worth looking into in the first link. it talks about bad ring gap.

 

[Sanford]

what brand piston did you use? did you check your ring end gap?

I bet it's not an assembly error. I'd look real hard at the carbs. group k has an article on partial throttle siezure. I remember that it said something about being at the torque peak and some carbs don't handle that situation well.

Pro-X pistons. My favorite brand and used them for years.

The carbs are pair of stock 38's off a SJ...again...this is all pretty standard stuff.

 

[the only couch rider]

saki sabotaged you simple as that

 

[Sanford]

UPDATE:

I've got new pistons, bore cylinder tomorrow and new 37cc (smaller) domes from Blowsion coming 2-day air. I'm also putting back a stock CDI just in case (at least for the break-in period). This is going to be sooooo close...

If I can't finish a solid day of water testing after setup again, I will not push it and save it for another day. At the very least, I will be bringing all my fancy camera gear and will be a on the beach shooting pix....but I'd rather ride.

 

[FLY6584]

What kind of guage were you using? I'm running 35cc domes and on my buddies guage it says I'm running 200psi and on my guage it says 185psi.

 

[Sanford]

It isn't a fancy gauge but as a reference, I put a stock head on it and it was dead on at 150psi! So I know the gauge is pretty close to correct.

For break-in I'm going to detune a little.

 

[douglee25]

Just a guess here, but if you were at partial throttle coming back to the dock, you were probably in the low jet circuit. 72.5 for a low jet seems on the lean side or border line anyway. I would fatten up the low side 78 maybe?

Thoughts?

Edit: Have you tried reverse jetting on the 38's? I'm pretty certain your 72.5 low jet was the cause of your seizure.

Doug

 

[Sanford]

I'm pretty certain your 72.5 low jet was the cause of your seizure.

I had a Blaster with same motor (mod pipe also) with a #70 pilot jet and never had an issue. Besides, Factory pipe also suggests #70.

This motor is setup as a very typical "limited" and this same package has been used many times, this is why I've pretty much eliminated jetting as the issue.

If this was a "lean" seizure then there would be pretty heavy scoring on mostly the exhaust port. Not the case here. Also, if this was caused by the pilot jet being too small, one would feel hesitation just off idle. Ski had a smooth powerband with no gurgling, transition gaps or anything.

BTW: Thanks everyone for the ideas, I appreciate all of them.

 

[SkiDaddy]

Sorry to hear about the problems Sanford. It looks like it may have been a 4 corner seizure, can't really tell from the pics. You probably can lighyly sand & reuse the pistons;muriatic acid may have cleaned the aluminum off the cylinder walls.

Anyway, some things to check:

1. Did it hold 6 PSi for 6 minutes?
2. Was the premix ratio correct?
3. Check the tank breather valve; if it's not working right or there's an obstruction it'll run lean.
4. Check the fuel filters in the carbs & main fuel filter.
5. On my ported 701 I was running 77.5 pilots & 137.5 mains w/OEM 38s. I'd richen up the pilots; it won't hurt anything.
6. You may have had too much water if you're running dual cooling. Consider running restricters during the winter.
7. Was the other piston damaged at all? If not, narrow your search. Perhaps a seal blew out.

 

[Sanford]

1. Did it hold 6 PSi for 6 minutes?
2. Was the premix ratio correct?
3. Check the tank breather valve; if it's not working right or there's an obstruction it'll run lean.
4. Check the fuel filters in the carbs & main fuel filter.
5. On my ported 701 I was running 77.5 pilots & 137.5 mains w/OEM 38s. I'd richen up the pilots; it won't hurt anything.
6. You may have had too much water if you're running dual cooling. Consider running restricters during the winter.
7. Was the other piston damaged at all? If not, narrow your search. Perhaps a seal blew out.

1) In the rush, I failed to do a leakdown test :banghead: Won't happen again.

2) 32:1 for initial break-in period (4 gallons). 40:1 after. Yes I know this is debatable but I've done it like this in the past plenty of times.

3) Check valve works like it should. Nothing blocking vents or fittings.

4) New fuel filter, carbs completely tore down and cleaned.

5) I'll be fatting up all jets to be perfectly safe. I just want to get past the critical break-in period so I can really get into dialing it in. Thanks for the jetting specs.

6) The water temp at lake was 70 degrees and had my hands on pissers most the time - they felt just fine (not too hot, not too cold).

7) Front piston was fine. But honestly I wasn't really pushing it and had I, I'm sure they both would have stuck. All new seals, no seals blew out.

Checked crank...its perfectly at 180 degrees.

BTW: What N/S & spring did you use and how heavily ported with what head?

 

[WaveDemon]

7) Front piston was fine. But honestly I wasn't really pushing it and had I, I'm sure they both would have stuck. All new seals, no seals blew out.

don't forget to check the ring gap, if it's too small the rings will wipe away the lubrication.

 

[sjetrider]

60 minutes into my easy "break-in" ritual I was heading back to shore doing 15 or 20mph (3K to 4K rpm - constant speed for 200ft) then it gently (if there is such a thing) siezed. I say gently because after it seized it started up...but I only idled to shore. Tore top end down and my rear piston is toast.

The story is very odd however and many things just don't add up. I check compression and its 195psi on the front (good cyl) and 190 on the rear (seized cyl). The odd thing is I am using 35cc domes and should have a mathematical compression of 185psi...not 195psi.

It gets even more odd. I made the mistake of not double checking the new bore clearance (piston to cylinder wall)...in the rush I "assumed" the machine shop did their job. Turns out there is .065" piston clearance. While this is a little high, certainly not the cause of the siezure. If nothing else, it would/should have helped with the greater clearance...not caused it.

Carbs were jetted right (135/72.5) and screws were fat. Base gasket was mint. Cases sealed well.

I'm scared to re-bore it and throw new pistons in it because I didn't find anything really wrong.

The only 2 things really odd is the larger clearance cylinder and I'm using a Blowsion billet head (with 35cc domes - on non big-bore 61x).

I am so sick about this because it just doesn't make sense. If I found the problem during disassembly, I would rush to bore, new pistons and get this done....but without a clear reason...:banghead:

Ran fantastic for the first 59 minutes.

I hope this is .0065" and if it is this is not your issue. If you have 190 comp in bad cylinder, my guess is lack of octane siezer. You said the piston was toast? how? Is it melted, chipped out on exhaust side above upper ring, were they in right? Switch domes to 36cc or run 100 octane.

 

[FLY6584]

I had a Blaster with same motor (mod pipe also) with a #70 pilot jet and never had an issue. Besides, Factory pipe also suggests #70.

This motor is setup as a very typical "limited" and this same package has been used many times, this is why I've pretty much eliminated jetting as the issue.

If this was a "lean" seizure then there would be pretty heavy scoring on mostly the exhaust port. Not the case here. Also, if this was caused by the pilot jet being too small, one would feel hesitation just off idle. Ski had a smooth powerband with no gurgling, transition gaps or anything.

BTW: Thanks everyone for the ideas, I appreciate all of them.

I'm running 70 pilots and 135 mains on my stock 701 with bpipe, 38's, and ada head(35cc domes) and it runs perfect. I did go a little fat on my screw settings to play it safe. I dont ever really run WOT either.

 

[SkiDaddy]

1) In the rush, I failed to do a leakdown test :banghead: Won't happen again.

2) 32:1 for initial break-in period (4 gallons). 40:1 after. Yes I know this is debatable but I've done it like this in the past plenty of times.

3) Check valve works like it should. Nothing blocking vents or fittings.

4) New fuel filter, carbs completely tore down and cleaned.

5) I'll be fatting up all jets to be perfectly safe. I just want to get past the critical break-in period so I can really get into dialing it in. Thanks for the jetting specs.

6) The water temp at lake was 70 degrees and had my hands on pissers most the time - they felt just fine (not too hot, not too cold).

7) Front piston was fine. But honestly I wasn't really pushing it and had I, I'm sure they both would have stuck. All new seals, no seals blew out.

Checked crank...its perfectly at 180 degrees.

BTW: What N/S & spring did you use and how heavily ported with what head?

1.5 N&S, I think it was a 65 gram spring. Porting was a mild race port massaged by Paul for better low end. 190 PSi comp. 33cc domes, 81.5mm pistons. It ran well till I melted a piston from having (unknowingly) a 650 headpipe.

I did do sustained WOT runs too. Many times.

 

[SkiDaddy]

Oh yeah, remebered I have an MSD & was running 3 degrees initial advance.