SXR SXR 850 Lites - Piston pic

[vcolf]

Decided to put the new endoscope I just bought use. First thing I wanted to do was take a look at the pistons after 3 hard seasons. I heard a lot of people saying timing advanced with stinger and a 850 is too much. Piston wash looks pretty decent to me. wondering what our resident expert think? A little fat?

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[Octane_114]

What's your oil ratio? Nothing wrong with being rich/fat. dont know the engine set up like if it is OEM and bored out or if the cylinders were resleeved with thicker sleeves but watch the transfers for cracking. I can only assume you turning/spinning it up tight. High rpms.

 

[MTRHEAD]

Looks nice

 

[vcolf]

Thx. 40:1 klotz r50 stock cylinder/sleeve bored to 1 under last bore. Its a stock class boat


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[vcolf]

spinning around 6800


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[Mg96]

Decided to put the new endoscope I just bought use. First thing I wanted to do was take a look at the pistons after 3 hard seasons. I heard a lot of people saying timing advanced with stinger and a 850 is too much. Piston wash looks pretty decent to me. wondering what our resident expert think? A little fat?

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Your sxr 850 has held together with advance timing, and exhaust restrictor? Did you use weisco , am in the process of building one, I'm kinda nervous about ignition and restrictor. Should I be? Do you run any special fuel, Did you set it up ,?

 

[vcolf]

it held up, pump gas. My compression was about 175 and I am not running an advent ignition. I think if I was running the same mods with advent or > 175 comp, I would run some race gas


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[Mg96]

it held up, pump gas. My compression was about 175 and I am not running an advent ignition. I think if I was running the same mods with advent or > 175 comp, I would run some race gas


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Are you running the plate advance sensor or flywheel cocked?

 

[vcolf]

advanced plug and stinger only


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[Mg96]

advanced plug and stinger only


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Did you have group k bore cylinders or local machine shop? Do you know what they set the piston to cylinder wall clearance?

 

[vcolf]

I don’t run wiseco piston just pro x or oem. Wiseco needs either a big ring gap or long break in for race skis.


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[vcolf]

Art at Jetworks does all my work. Give him a call


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[Mg96]

I don’t run wiseco piston just pro x or oem. Wiseco needs either a big ring gap or long break in for race skis.


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You cant 850cc using a cast piston. 83mm is largest. Weisco and wossiner are only option for 85mm both are forged.

 

[vcolf]

That could be correct I think I started at 83 cast and freshened up the top end going to 84. I think art had a hidden stash and pistons that might’ve been cast but someone could call him and check. he’s definitely known to have some speciality stuff


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[vcolf]

also if you’re coming from the stock bore I recommend starting at 83 to leave a few bores and keep the comp down with timing advance. I noticed a decent different just going up to 83. at 84+ the sleeves start to get pretty thin and you risk the lower sleeve cracking. In lites class you can’t machine that part of the sleeve so you’d have to just leave it and risk it


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[Storbeck]

I don’t run wiseco piston just pro x or oem. Wiseco needs either a big ring gap or long break in for race skis.


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I'm trying to figure out why the ring gap or break in time would be affected by who makes the pistons, and also why ring gap and break in time would be related in any way.

 

[Mg96]

I'm trying to figure out why the ring gap or break in time would be affected by who makes the pistons, and also why ring gap and break in time would be related in any way.

Forged pistons like weisco and wossiner expand more than a cast piston like pro x or stock. Also there are different ring manufacturers and materials that have different break in times

 

[te4250]

Yeah I never thought the higher CTE of forged pistons affected ring end gap just piston-cylinder clearance. Isn't ring end gap just an function of bore and expected cylinder temp.