Author Topic: RM bearing/alum washers mod VS Re-pinned YZ piston (Read 1037 times)

James Dandy · « **on:** September 25, 2013, 08:38:24 pm »

Just wondering if anyone has tried both. What are the pros and cons? Has anyone weighed the two? If so, which one is lighter? The thing that I guess bothers me about the RM bearing deal, is if the steel thrustwashers break easily, then wouldn't aluminum break easier? What's the best setup for high compression/high rev applications. I don't want it to be a ticking time bomb, but I plan on frequent top end checkups, so reliability isn't the only factor I'm weighing.

El Diablo · « **Reply #1 on:** September 25, 2013, 09:48:07 pm »

I haven't tried the FTZ setup with the pinned YZ-250 piston but I have heard feedback from those who have. The biggest complaint is the tiny pins falling out which lets the rings spin around & catch a port. When that happens, not much else matters. As far as weight goes, I couldn't tell you which is lighter. Now on my zilla, I run the RM bearing with billet aluminum thrust washers & have never had any problems in the 3 years I've been running it. Some guys here spin their zillas up to 9,000 rpm & have no issues with them. But a YZ-250 piston would not fit a zilla either, it's just for the LT-250Rs.

Cunningham_821 · « **Reply #2 on:** September 25, 2013, 10:13:43 pm »

No use reinventing the wheel bro... Ive seen the repinned yz pistons. Ask yourself this do u really want to have to get a custom piston made every rebuild? Id go with the billet washer and rm bearing and never look back. That is my opinion tho. The reason the oem washers fail is that the material is case hardened which destroys motors ive seen the damage personally. Even if a billet washer would fail which ive never heard of in my time in the lt world it wouldnt do nearly the damage the oem washers do. My washers have lots of hard passes on and dont have the slightest bit of wear on them. Good luck w/ ure build.

Stpltn250r · « **Reply #3 on:** September 26, 2013, 05:39:43 am »

LT250RWV · « **Reply #4 on:** September 26, 2013, 05:48:36 am »

I believe Iceracer said the yz re pin comes apart in another thread. I have ran billet washers rm bearing Not one problem from the setup. Alot of us run billet washers and rm bearing havent heard one horror story like the stock washer.

Glamisrider · « **Reply #5 on:** September 26, 2013, 07:46:30 am »

AL is not as brittle as steel so they are less likely to come apart and if they do Al is a LOT softer than steel so when the pieces go through your motor there is MUCH less damage.

Run the AL thrust washers and forget about it, you're just asking for trouble going the other route.

MotorGeek - Jerry Hall · « **Reply #6 on:** September 26, 2013, 08:48:41 am »

Quote from: James Dandy on September 25, 2013, 08:38:24 pm

Just wondering if anyone has tried both. What are the pros and cons? Has anyone weighed the two? If so, which one is lighter? The thing that I guess bothers me about the RM bearing deal, is if the steel thrustwashers break easily, then wouldn't aluminum break easier? What's the best setup for high compression/high rev applications. I don't want it to be a ticking time bomb, but I plan on frequent top end checkups, so reliability isn't the only factor I'm weighing.

Why are you considering a YZ piston when you can still buy pistons that are made to fit yur engine without any modifications? Re-pinning the ring end gap is expensive and is never as reliable as the original pin installation.

High performance two stroke engines require frequent tear downs, inspection and piston replacement. Pistons ware/collapse, fatigue, crack and then break. It is up to each owner to tear down and inspect their top ends frequently to determine how often your engine and riding style necessitates the piston to be changed.

It is not uncommon for guys to be able to replace the piston 3 or 4 times on the same bore if you keep dust from getting past the air filter and run a lot of oil in the fuel.

ZeroZeroMinusOne · « **Reply #7 on:** September 26, 2013, 01:54:57 pm »

In a properly setup motor how long can the AL thrust washers last before they need replacing? I know its a pretty broad question but "in general" should they be replaced after each rebuild or what?

MotorGeek - Jerry Hall · « **Reply #8 on:** September 26, 2013, 05:03:02 pm »

If they do not show any visible ware on the sides, the pin still fits tight in the washer and there are not any cracks I would reuse them. Excessive clearance is what causes the OEM washers to fail. We make our washers so that there is less than .0005" clearance. We have rebuilt engines that have had our billet washers in them for years and they are still tight when we tear down the top ends. We have torn down top ends that had billet washers that were not made by us and some of them had over .010" clearance between the pin and hole in the washer but were ****.

To date, I have not worked on an engine where the aluminum thrust washer broke and chewed up anything.

Dezsled · « **Reply #9 on:** September 26, 2013, 05:45:57 pm »

Jerry, the top end you did for me, how many hours do you suggest running before reringing and total piston replacement?

PCS · « **Reply #10 on:** September 26, 2013, 05:57:29 pm »

http://www.ctracing.com/cylinder.htm

line 3 haha

James Dandy · « **Reply #11 on:** September 26, 2013, 06:51:57 pm »

Okay. I just wanted to be sure that I was already convinced on the aluminum washers. And I am. So that's the way im going. Now on to my piston... My local shop (G and R motor ports Walton Ky) is gonna do my bore and hone after I decide on my Piston. I haven't got a set of inside mics yet, but with the dial calipers at the top of the bore, it measures 68.45mm, in both directions, then measuring at the bottom it measures 68.5mm. This is after I ran a few passes cylinder hone through to clean it up.
There is no visible scarring on the cylinder, but the piston was toast. All scarred up at intake and exhaust ports. There were no thrust washers in place.
I used to like the black oxide vertex race pistons. They lasted forever in my YZ125. I guess that's why I was hung up on the YZ piston thing for a minute. I've never been a fan of weisco. Seems like every broken blaster piston I've seen was a wiesco. Anybody know of a similar coated piston for the LT250R? If not, which should I get?
Motorgeek, so does your company produce the aluminum thrust washers? If so, could I get a list of your related products/services, and prices please? My email is public on here, if u want you can send it to me. I can foreward the info to my local shop if u want. One of the owners loves old Suzuki 2-stroke stuff.

LT250RWV · « **Reply #12 on:** September 26, 2013, 09:05:21 pm »

I think blaster bust their piston up because of no thrust washers alot of side to side when the piston is on the pin. I never understood why they done that. I can go from first hand about not running thrust washer in the lt.it run with out them but the piston doesnt last to long or the pin that hold the rings in place either. New owner and didn know about any forums at the time. Also wiseco said I didnt need them. Hell they make the piston and didnt know.

PCS · « **Reply #13 on:** September 26, 2013, 10:52:38 pm »

Mitch is the one that sells the billet washers with the rm bearing combo.look at the forum store for details

Nopick · « **Reply #14 on:** September 27, 2013, 04:03:06 am »

After MotorGeek's comments about thrust washer to wrist pin clearance needing to be .0005 inches to insure the washers do not crack, does anyone know what clearance Mitch's washers have?

James Dandy · « **Reply #15 on:** September 27, 2013, 06:20:33 am »

Sweet. Thanks to all the contributions to this thread. .0005 is mighty tite! I do not have precise enough instruments to een measure that, but I'm wondering if these washers should be hand lapped. I'm gonna order these as soon as i decide on a piston. I'd really like to find someone who would put the black oxide coating on a wiesco for me, that is unless pro x or someone already makes a coated piston for the LT

MotorGeek - Jerry Hall · « **Reply #16 on:** September 27, 2013, 08:31:56 am »

Quote from: LT250RWV on September 26, 2013, 09:05:21 pm

I think blaster bust their piston up because of no thrust washers alot of side to side when the piston is on the pin. I never understood why they done that. I can go from first hand about not running thrust washer in the lt.it run with out them but the piston doesnt last to long or the pin that hold the rings in place either. New owner and didn know about any forums at the time. Also wiseco said I didnt need them. Hell they make the piston and didnt know.

The blaster engine/piston is typically running within a few degrees of death at all times Air flow to the cylinder is blocked by the frame tubes, shocks, bumper, and exhaust pipe. We typically bore 5 to 10 times as many blaster cylinders as any other cylinders. Most of the blasters cylinders look like nuclear melt downs. Any engine in a Quad or three wheeler should be liquid cooled unless it is a drag only engine

The majority of the blasters we tear down and cylinders we bore that were still running before tear down have sighs of piston scuffing and mild seizures. Mild seizures and piston scuffing increases the piston to cylinder wall clearance very rapidly and destroys the strength of the piston skirts

Excessive piston to cylinder wall clearance is the only thing that makes pistons crack and then break.

The job of the thrust washers anywhere on the connecting rod is to center the rod between the crank webs. Thrust washers do not influence the thrust in any direction on the piston against the cylinder wall.

MotorGeek - Jerry Hall · « **Reply #17 on:** September 27, 2013, 08:35:42 am »

Quote from: Dezsled on September 26, 2013, 05:45:57 pm

Jerry, the top end you did for me, how many hours do you suggest running before reringing and total piston replacement?

I would take the top end off and inspect it after 15 to 20 hours. Make you next scheduled tear down and parts replacement based upon what you find on the first inspection

MotorGeek - Jerry Hall · « **Reply #18 on:** September 27, 2013, 08:58:00 am »

Quote from: James Dandy on September 26, 2013, 06:51:57 pm

Okay. I just wanted to be sure that I was already convinced on the aluminum washers. And I am. So that's the way im going. Now on to my piston... My local shop (G and R motor ports Walton Ky) is gonna do my bore and hone after I decide on my Piston. I haven't got a set of inside mics yet, but with the dial calipers at the top of the bore, it measures 68.45mm, in both directions, then measuring at the bottom it measures 68.5mm. This is after I ran a few passes cylinder hone through to clean it up.
There is no visible scarring on the cylinder, but the piston was toast. All scarred up at intake and exhaust ports. There were no thrust washers in place.
I used to like the black oxide vertex race pistons. They lasted forever in my YZ125. I guess that's why I was hung up on the YZ piston thing for a minute. I've never been a fan of weisco. Seems like every broken blaster piston I've seen was a wiesco. Anybody know of a similar coated piston for the LT250R? If not, which should I get?
Motorgeek, so does your company produce the aluminum thrust washers? If so, could I get a list of your related products/services, and prices please? My email is public on here, if u want you can send it to me. I can foreward the info to my local shop if u want. One of the owners loves old Suzuki 2-stroke stuff.

Measuring the bore at the top and bottom of the cylinder does not tell you anything about the inside diameter of the cylinder between those two measurements you are taking. The piston does not live at the top and bottom of the bore, it spends most of it's life between the ends of the cylinder.

Digital or dial calipers are only good for taking quick and approximate measurements. The life span of any caliper is short because the measuring surface of the thin blades ware quickly. The accuracy is usually poor and not the proper tools to use when measuring piston clearance or ANYTHING that requires accurate measurements.

A bore gage is the proper tools to use when measuring a bore for roundness and straightness. An inside micrometer is many times better than using a feeler gauge or calipers but is very difficult to operate accurately in the middle of the cylinder on these small quad bores.

Glamisrider · « **Reply #19 on:** September 27, 2013, 09:09:50 am »

Quote from: Dezsled on September 26, 2013, 05:45:57 pm

Jerry, the top end you did for me, how many hours do you suggest running before reringing and total piston replacement?

Dez I have a 87 top end done by Jerry and I get 33-40 hours MAX out of a piston. Basically every season I need a new piston due to the skirt cracking.

The last one had 34/35 hours on it and it has a 1/2 inch crack on one of the cut outs, no damage but it has a crack.

That was the 3rd piston on that bore so we'll see if it gets a 4th or it needs a bore.

Dezsled · « **Reply #20 on:** September 27, 2013, 10:51:02 am »

Thanks for the info guys...

Jerry what's the recommended piston to cylinder bore clearance?

LT250RWV · « **Reply #21 on:** September 27, 2013, 01:09:40 pm »

But Jerry not having thrust washer that would cause the piston not to stay centered on the rod. Wouldnt that cause damage The 2 motors I ran without thrust washers lasted 1 year. Since adding your billet washer the piston I have now is a year and still looks good.

Rider414 · « **Reply #22 on:** September 27, 2013, 01:48:11 pm »

Quote from: Glamisrider on September 27, 2013, 09:09:50 am

Quote from: Dezsled on September 26, 2013, 05:45:57 pm
Jerry, the top end you did for me, how many hours do you suggest running before reringing and total piston replacement?

Dez I have a 87 top end done by Jerry and I get 33-40 hours MAX out of a piston. Basically every season I need a new piston due to the skirt cracking.

The one I just pulled has 34/35 hours on it and it has a 1/2 inch crack on one of the cut outs, no damage but it has a crack.

This is my 3rd piston on this bore so we'll see if I get a 4th or it'll need a bore.

I assume these are all dune hours?

B_Fuss · « **Reply #23 on:** September 27, 2013, 03:38:57 pm »

Dune hours yup.

James Dandy · « **Reply #24 on:** September 27, 2013, 06:44:33 pm »

FWIW, the piston in the motor I've got torn apart also has a crack in the skirt. About 1". This motor did not have thrust washers, and was really ruff tho.

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Author Topic: RM bearing/alum washers mod VS Re-pinned YZ piston (Read 1037 times)

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