ISDE Aftermath

[SpeedyManiac]

Hi guys,
I finally got my bike back from the ISDE and tore it down this evening. The piston seized in two spots on the exhaust side, right by the side exhaust ports. Must've been too lean on the needle, but I still don't get why it did it at the end of the day instead of the start.

The cylinder needs to be replated and a new piston and rings installed, but that seems to be the only damage. Bottom end looks good, same with the rod, head, etc. The question is, do I bigbore or not. I'm thinking of making it a 275...Opinions?

 

[iancp5]

Looks a similar seizure to mine recently. I was running very lean in tight woods, when I did a more open Rally type event and it was held at constant speed a slight restriction in fuel flow pushed it over the edge.

As for 275 I'm the wrong person to comment - I have a 300 but would like a smaller motor. If I lived anywhere near you I'd offer to swap!

 

[cladoo]

I think it was that deeper sand with the needle too lean that did it in. I used to ride in sand alot and we had to go up on the main also.

 

[Berkyboy]

At the last minute, just before impounding in Chile, we jetted Brian Hasslen's 300 a little fatter then he was using on the test track in La Serena.

His 300 is a little less finacky when running rich, compared to how a 250 would run, and we decided it would be safer to run rich for the first day and adjust the jetting leaner later on if we needed too.

The first mistake a lot of Six Days "first timers" do is run too lean of jetting and over the year's, I've been to 12 Six Days, I've seen a lot of riders make that mistake and lean sieze.

A good Day-One Six Days approach is to run your jetting on the safe side, at least until you figure out how your bike is going to run using local fuels. The jetting track gets you close but there's no replacement for a couple hours in the saddle under race conditions.

From some of your more recent posts it sounds like your comfortable shooting for a silver medal this year ( in Greece ) and a little fatter jetting isn't going to keep you off that pace.

 

[SpeedyManiac]

Hey Steve,
Lesson learned. Silver in Greece is my goal. I was on silver in Chile when my bike died and I wasn't overly comfortable in the sand or special tests. Greece looks like the terrain around here so hopefully I'll do better there.

I'm also still toying with tryiing the Romaniacs, but I gotta do a lot of fundraising to afford both races and a month in Europe. We'll see.

 

[Berkyboy]

If your budget can afford it I'd go for the complete 300 stock cylinder, head and piston, that way if you need to do a top end either between or during Romanics or Six Days you'll be able to find parts.

 

[SpeedyManiac]

I'll probably rent for this year's Six Days since I can easily bring my suspension, bars, etc from home to Greece (and possibly Romania).

I'm not sure if I want to modify the motor or not. It already makes good power (though it could make a little more in the open stuff) but I don't want to screw up the power delivery. Right now it's magic. It lugs down low as good as any thumper, yet it pulls hard all the way into the over-rev. It'd be nice to have a bit more meat in the midrange, but not at the cost of changing the delivery.

 

[REVERUP]

Isn't the saying go big or go home!.

No really , from the photos Ive seen of you, you don't look like you weigh allot and if you like the delivery of the 250 I would put it back to stock displacement.

I need the extra ooomph of a 300 to motivate my 225LB's with gear on, so I would personaly welcome more displacement.

 

[widebear]

Lets have a look at the underside of that piston. At this point i'm not totally convinced of the diagnosis, the reason being i dont see alot of damage at the exhaust side of the piston.I would want to know the existing piston to wall clearance before making assumtions.Ps Speedy will you keep the piston so that I can weigh it for a future registry?

 

[SpeedyManiac]

I'll post a picture of the underside of the piston. My buddy thinks the jetting was fine, but that somehow the cylinder was suddenly cooled on the exhaust side (splashing water from creek crossings, maybe).

I'm planning on keeping the piston as once expensive souvenir from my first ISDE. And it's a reminder to triple check everything. Why do you want to weigh it?

 

[GMP]

It is a little odd that it didn't squeak on the exhaust side more. Why does your PV look like its rusty (second pic down) ?

 

[SpeedyManiac]

There's a little bit of rust on the PV from shipping home from Chile. Must've been a bumpy/wet ride home, since any bare metal on the outside has surface rust. Doesn't look like the bottom end has affected.

Note: If you're ever shipping a bike by boat across an ocean, WD-40 all bare metal! My bike was fine going down to Chile, but coming home it got a lot of surface rust.

 

[PEB]

My bike gets some sort of oil after every ride/wash. It stays clean shiny and rust free that way.

Paul B

 

[widebear]

I would like to know what the differance in weight is between the various brands. vertex , wossner, wiseco .piston ,rings and pin

 

[SpeedyManiac]

I see. Well, mine is permanently with rings and minus a bit of material on the side so you won't get an accurate measurement.

I'd guess there's very little weight difference.

I don't usually spray down everything with WD-40 because I like to ride 3-4 (sometimes more) times a week. I don't have time to wash it every single time I go riding. Only for races and maintenance.

 

[gasgasman]

I honestly don't think you ran it lean.
The top of the piston is too clean.
When a bike is ran lean, it would start detonating which would start pitting the top of the piston.
The entire circumference of the piston would be scored up also.

If I was to guess, I would say the piston was out of round. Possibly mismachined.

 

[GMP]

That bike had a few hours on it before ISDE, right? I would think if the piston or clearance were at fault, it would have happened sooner.

I doubt splashing water would do it, everyone does that all the time. Plus the entire water jacket and warm coolant would act as an stabilizer.

Maybe it ran OK (not lean) most of the day and went lean suddenly, under load in the sand, heated up quick and seized. What did you do with the carb vent lines? Clogged with sand would affect venting and also could pull sand in and partially block the main jet. This has happened to me. Girrard is right the piston dome looks dark, like it was rich for awhile if anything.

Cooling system OK?

Just a few thoughts.

 

[SpeedyManiac]

I'll take a look at the carb vent lines.

I had maybe 2 hours on the top end before the start of the ISDE (I rebuilt it shortly before shipping, then had a bit of testing on it down in Chile). It had run flawlessly for over 7 hours during the day before it seized so I really doubt the piston clearance was an issue.

 

[widebear]

I'll take a look at the carb vent lines.

I had maybe 2 hours on the top end before the start of the ISDE (I rebuilt it shortly before shipping, then had a bit of testing on it down in Chile). It had run flawlessly for over 7 hours during the day before it seized so I really doubt the piston clearance was an issue.

You will never know if you dont check.The clearance may have been tight to start out with and not been a problem till an unexpected entered the equation. I'll bet as it stands your under 2 thou piston to wall clearance.

 

[SpeedyManiac]

I measured the clearance with the buggered piston/cylinder and it's at about 4 thou. Not extremely accurate with the scored cylinder/piston, but it gives a ballpark number. I can't remember what it was when the new top end was put in it before I sent it to Chile, but I know it was within spec.