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SXP

Thumper Racing in Texas

31 posts in this topic

Anyone have any experience with this company's big bore kits? www.thumperracingusa.com

After a two week wait I've just received my 430 kit for my '99 WR400, only to find they have sent me an incorrect piston/piston pin combo. The pin is way too big for the small end of the connecting rod. Cross referencing the piston (95 mm WISECO ) part number they sent me with WISECO's web site, I see it's the standard replacement piston for the YZ/WR 426's. I'm pretty sure the connecting rod small-end is different (bigger) on the 426's. I hope we haven't crossed a point of no return here, and it's just a goof-up on their part 'cause looking at the available sizes on WISECO's website for YZ/WR400's they don't make a 95 mm piston (which is what they sleeved my cylinder for) for the 400's. They (ThumperRacing) have to have known the small-ends are different and I'm really hoping it's just a screw-up and I'm not expected to also change out my connecting rod.

Unfortunately I received the kit Friday afternoon and the company was closed, so I'm anxiously waiting for Monday to get this sorted out. I was hoping to ride this weekend:mad:. Bummer!

I'd be really interested in hearing feedback from anyone who has used their kit before. What are your impressions on power, durability, reliabilty etc.

Thanks.

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My WR motor was a Thumper Racing 420 cc engine. The power was great! The connecting rod split in two and broke the cases, but I believe that has NOTHING to do with the kit they build. The connecting rod is from the factory, and it split length-wise. When I tore the motor apart I pushed the piston out of the cylinder with no binding. It was definitely just a failure of the connecting rod. I'll probably use them again to rebuild the YZ motor I got to replace the WR one. Hope that helps!!

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SXP, do you think the cylinder was likely bored at 95mm for the 94.5mm piston?

That's how the 440 kit on my DRZ is done and I am using the Wiseco BB kit.

Dan

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The Wiseco box the piston came in says it's a 95 mm piston and I imagine the cylinder is sleeved for it.

They bore out the stock Nikasil coated aluminium cylinder and press a metal sleeve in (no fancy coating on it) to give you the extra displacement.

Just spoke to ThumperRacing and apparently they sent me a piston for the 426's (different wrist pin size). Also, they sent me a pilot jet that is physically too big to fit in the carb :-((.

Anyway, they are calling Wiseco to get me the correct piston, and hopefully get me the proper pilot jet too. Hopefully we'll have a happy ending here. Let's see how this works out. I'll keep you guys updated.

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They bore out the stock Nikasil coated aluminium cylinder and press a metal sleeve in (no fancy coating on it) to give you the extra displacement.

That's what the machine shop used for my 440 kit. Mill out the plated-aluminum cylinder and sleeve with a steel liner.

A lot of folks complain about motors wearing out alot faster with the steel sleeve vs. the coated liner...

Time will tell.

Dan

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True. When discussing this upgrade with the ThumperRacing head mechanic, he mentioned that the OEM Nikasil coated aluminium cylinders are so hard that the pistons always wear out and the cylinder hardly ever does. However, with the big bore kit steel sleeve, the sleeve wears faster than the piston (or at least equally).

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Hey Burned, the guy at the Machine Shop has had trouble with headgaskets on the 13.5 setups just like you said...

12.5 seems to be reliable though...

Got my fingers crossed!

Dan

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ive got my fingers double extra crossed for you.all the problems ive had with them has been the 12.5 to 1.im the only one ever running the 13.5 to 1 besides a couple other guys ive done motor for.

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Update: After calling Thumper Racing and explaining what happened (see below) I received another piston in the mail; however, while it was a piston for the YZ/WR 400's (correct wrist pin size), it was a 94 mm piston. The sleeve they pressed in is for a 95 mm piston. So, after another phone call, they are trying to determine what's going on. Needless to say, I'm getting really anxious. I'm taking comfort in all the positive things people on this forum have to say about the company and am really hoping they can work this out. Hey, I haven't lost my cool yet!

Standby for an update....

Anyone have any experience with this company's big bore kits? www.thumperracingusa.com

After a two week wait I've just received my 430 kit for my '99 WR400, only to find they have sent me an incorrect piston/piston pin combo. The pin is way too big for the small end of the connecting rod. Cross referencing the piston (95 mm WISECO ) part number they sent me with WISECO's web site, I see it's the standard replacement piston for the YZ/WR 426's. I'm pretty sure the connecting rod small-end is different (bigger) on the 426's. I hope we haven't crossed a point of no return here, and it's just a goof-up on their part 'cause looking at the available sizes on WISECO's website for YZ/WR400's they don't make a 95 mm piston (which is what they sleeved my cylinder for) for the 400's. They (ThumperRacing) have to have known the small-ends are different and I'm really hoping it's just a screw-up and I'm not expected to also change out my connecting rod.

Unfortunately I received the kit Friday afternoon and the company was closed, so I'm anxiously waiting for Monday to get this sorted out. I was hoping to ride this weekend:mad:. Bummer!

I'd be really interested in hearing feedback from anyone who has used their kit before. What are your impressions on power, durability, reliabilty etc.

Thanks.

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ive got my fingers double extra crossed for you.all the problems ive had with them has been the 12.5 to 1.im the only one ever running the 13.5 to 1 besides a couple other guys ive done motor for.

\ I have never had sealing issues with mine set up at 14~1.

It is an assembly prep issue to maintain sealing integrity.

I would never compromise the cooling with a sleeve, I would stick with a fancy coating. No pun...

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I have never had sealing issues with mine set up at 14~1.It is an assembly prep issue to maintain sealing integrity.I would never compromise the cooling with a sleeve, I would stick with a fancy coating. No pun...

No pun taken! :D

Seriously though...I work in the two-way radio field and I deal with heat issues all the time with my radio equipment.

Granted, it's nowhere near the temps we're dealing with on engines...

However, we use RF transitors with steel components and they're strapped to aluminum to dissepate the heat.

You would think that the steel sleeve should be able to dissepate the heat just fine because it's wrapped in water-cooled aluminum...

I wasn't truly worried about heat, it's the wear-issue that I'm concerned with. Ah heck, it's just money and you can't take it with ya... :D

Next time, I'll just plate it.... :)

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I had the Thumper 436 kit in my DRZ400. I had a headgasket go at 200 miles. I caught the problem as soon as it happened, I saw the smoke and shut it down. When I opened it up there was almost no cross hatch left in the cylinder.

I would use full synthetic oil and just ride it until it starts to smoke.

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I had the Thumper 436 kit in my DRZ400. I had a headgasket go at 200 miles. I caught the problem as soon as it happened, I saw the smoke and shut it down. When I opened it up there was almost no cross hatch left in the cylinder.

I would use full synthetic oil and just ride it until it starts to smoke.

So, that leads me to ask....what'd you do afterwards?

Did you have it plated after that?

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ive got my fingers double extra crossed for you.all the problems ive had with them has been the 12.5 to 1.im the only one ever running the 13.5 to 1 besides a couple other guys ive done motor for.

\ I have never had sealing issues with mine set up at 14~1.

It is an assembly prep issue to maintain sealing integrity.

I would never compromise the cooling with a sleeve, I would stick with a fancy coating. No pun...

exactly.i run mine with aluminum sleeve and replated with no issues. my personal motor is 14 to 1.

i use these guys for all my big bore needs.

http://www.mt-llc.com/index_home.shtml

why take your motor back 10 years in technology?

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Update: They (Thumper Racing) can't find a 95 mm piston with the correct wrist pin size for a WR400!!!! So now I have a WR400 jug with a 95 mm sleeve that they pressed in but no piston to go with it. Turns out they had a special agreement with Wiseco to make these pistons and Wiseco stopped producing them and Thumper Racing is out of them. They are now grinding/cutting down some 95 mm piston to make it work for me. What a fiasco! I have a bad feeling about this. I'd back out of this but I'm about $500 in the hole with them and want them to make this right.

Did some one say these guys had their s@*t together? :)

Update: After calling Thumper Racing and explaining what happened (see below) I received another piston in the mail; however, while it was a piston for the YZ/WR 400's (correct wrist pin size), it was a 94 mm piston. The sleeve they pressed in is for a 95 mm piston. So, after another phone call, they are trying to determine what's going on. Needless to say, I'm getting really anxious. I'm taking comfort in all the positive things people on this forum have to say about the company and am really hoping they can work this out. Hey, I haven't lost my cool yet!

Standby for an update....

Anyone have any experience with this company's big bore kits? www.thumperracingusa.com

After a two week wait I've just received my 430 kit for my '99 WR400, only to find they have sent me an incorrect piston/piston pin combo. The pin is way too big for the small end of the connecting rod. Cross referencing the piston (95 mm WISECO) part number they sent me with WISECO's web site, I see it's the standard replacement piston for the YZ/WR 426's. I'm pretty sure the connecting rod small-end is different (bigger) on the 426's. I hope we haven't crossed a point of no return here, and it's just a goof-up on their part 'cause looking at the available sizes on WISECO's website for YZ/WR400's they don't make a 95 mm piston (which is what they sleeved my cylinder for) for the 400's. They (ThumperRacing) have to have known the small-ends are different and I'm really hoping it's just a screw-up and I'm not expected to also change out my connecting rod.

Unfortunately I received the kit Friday afternoon and the company was closed, so I'm anxiously waiting for Monday to get this sorted out. I was hoping to ride this weekend:mad:. Bummer!

I'd be really interested in hearing feedback from anyone who has used their kit before. What are your impressions on power, durability, reliabilty etc.

Thanks.

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you need to think of what you will do if you need another piston in the future. wiseco will have standard overbore sizes. "cutting down" a piston should not be an option. to alter something like a piston is asking for trouble. it sounds like they need to press in the correct sleeve (94mm) or give you a new jug. they screwed up, not you. just my two cents.

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