FCR MX-39 first ride impressions

Fcr is actually a lot of bang for the buck

What changes with the rings when the piston is removed, then reinstalled properly?

The ring seal is disturbed , fit new rings for a true seal .

Some say ^^ that's crap .. Fine by me , use the old ones :excuseme:

What changes with the rings when the piston is removed, then reinstalled properly?

 

The rings have mated to the cylinder wall...

Removing the piston from the cylinder disturbs this mating that was achieved through "break in" procedure..

Upon reassembly the rings will never be re installed into the exact same position , so a poor seal is the result...

I hope this make sense ....

Ive gotten a few pm's about people that were on the fence and are now gonna order the TT kit,   some may even say IT'S GOT GNARLY POWER EVERYWHERE.  :smirk: 

Ive gotten a few pm's about people that were on the fence and are now gonna order the TT kit,   some may even say IT'S GOT GNARLY POWER EVERYWHERE.  :smirk:

 

The rings have mated to the cylinder wall...

Removing the piston from the cylinder disturbs this mating that was achieved through "break in" procedure..

Upon reassembly the rings will never be re installed into the exact same position , so a poor seal is the result...

I hope this make sense ....

Craigo, please dont take this as "arguementative" as I really am trying to see it from your "angle". You do realize the purpose of the cross hatch in the cylinder and why 2 stroke pistons have anti-rotation pins in the ring grooves/lands?

 

Ive gotten a few pm's about people that were on the fence and are now gonna order the TT kit,   some may even say IT'S GOT GNARLY POWER EVERYWHERE.  :smirk:

Sweet, thats great news, we appreciate the business!

Have to agree on the piston ring thing. Never heard of having to change rings on cylinder removal before, and I've reused mine without any issues... Unless they had to be replaced due to oil consumption.

 

Craigo, please dont take this as "arguementative" as I really am trying to see it from your "angle". You do realize the purpose of the cross hatch in the cylinder and why 2 stroke pistons have anti-rotation pins in the ring grooves/lands?

 

Sweet, thats great news, we appreciate the business!

 

 

Not being argumentative mate, just stating facts or should I say educated opinion.?....Most top engine builders will have the same opinion as me...

PM Eddie Sisneros and get his opinion if in doubt , he has built more DRZ engine than anyone I know..

I recall seeing his posts stating installing used rings is not advisable because of ring seal issues.

The other aspect to consider is "the while it's apart" thing....top end removal is time consuming and costly to some, if dismantled and has some miles on it, practically would encourage using a new set of rings..

Edited by Craigo 485sm

The rings have mated to the cylinder wall...

Removing the piston from the cylinder disturbs this mating that was achieved through "break in" procedure..

Upon reassembly the rings will never be re installed into the exact same position , so a poor seal is the result...

I hope this make sense ....

The rings have mated to the cylinder wall...

Removing the piston from the cylinder disturbs this mating that was achieved through "break in" procedure..

Upon reassembly the rings will never be re installed into the exact same position , so a poor seal is the result...

I hope this make sense ....

not only is there potential ring sealing issues but you can also fracture a ring when reusing you old rings

just to add, ring seal on a 2 stroke is not a real issue as oil in the combustion chamber is required......

which is not the case with a 4 stroke

Not being argumentative mate, just stating facts or should I say educated opinion.?....Most top engine builders will have the same opinion as me...

PM Eddie Sisneros and get his opinion if in doubt , he has built more DRZ engine than anyone I know..

I recall seeing his posts stating installing used rings is not advisable because of ring seal issues.

The other aspect to consider is "the while it's apart" thing....top end removal is time consuming and costly to some, if dismantled and has some miles on it, practically would encourage using a new set of rings..

 

No doubt a performance engine builder is going to recommend at least new rings when installing their parts. But I would say that 99% of that is due to them wanting you to have the best experience and maximum performance with their parts, not that they feel its due to ring seal or anything like that. Plus, they have no idea how much time or stress is on the rings. But then I would argue in that same case, to replace BOTH the rings and the piston, re-hone the cylinder and confirm piston wall clearance. Completely agree with you on the "while its apart", but ill get into that more in a minute.

 

not only is there potential ring sealing issues but you can also fracture a ring when reusing you old rings

 

You risk breaking a piston ring whenever they are removed or replaced whether new or used. And if you are just replacing a cylinder base gasket (swapping to the "E" model) why would you take the rings off anyways?

 

just to add, ring seal on a 2 stroke is not a real issue as oil in the combustion chamber is required......

which is not the case with a 4 stroke

 

Im not trying to muddy the water or get into too much off topic detail, but the reason I stated the 2 stroke piston having ring locating pins is that cross hatching causes the rings to wander around. In a 2 stroke this will cause the ring to snag a port and destroy the top end. Not an issue in a 4 stroke. The point being that rings wander around all day long as normal, this was in response to your statement about not being able to get them back in the same exact position (rotationally).

 

That being said you should never put new rings on UNLESS you also properly hone the cylinder, otherwise your risk of poor ring seal is actually much more likely in that case than just re-using your old rings as long as they were still serviceable. But then I would also say if your top end needs new rings and cylinder needs to be honed to do so, you should replace the piston as well "while you are already in there". Rings are extremely hard steel alloy. Your cylinder plating is even several times harder than that. Your piston is butter soft aluminum. Which metal is going to feel the most wear? If the piston is out of spec at all, brand new rings and hone will do nothing and ring seal will be crap due to the piston. Remember, ring stability is the pistons job. Once the lands and grooves are out of spec the rings wont be held square and ring seal goes away quick. New rings will do nothing in this aspec!

 

These are my experiences and opinions but to compare them to Eddie, I have only built motors in the "hundreds" in regards to "life time", where he probably builds them in the "hundreds" each year. The other difference is I have built Nitrous/Turbo/Blower V6's and V8's and other non-power sport related stuff as well. Those types of motors are far more likely to "cook" rings than to wear them out. So its more common to replace rings several times to each set of pistons. Rings have a tendency to loose tension due to heat stress quicker than the pistons skirt and ring lands/groves or wrist pin journal wear. So my experience is less focused on single cylinder dirt bikes than Eddie's. But I would find it hard to believe he would disagree with much of what I stated in my previous paragraphs?

 

I agree with the majority of what you said, The short skirted pistons nowadays wear quicker than the piston rings, so in the case of worn piston, I would always suggest piston and rings replacement as a set..

For those who wish to reuse low hour rings, fine, but a light cylinder hone should be done to help with ring seal..

Me , myself and I will always continue to replace rings when the slug is pulled from the jug..... :D

Edited by Craigo 485sm

Yeah , we can mix this up some more .. What's the best oil to use with the used rings I just installed . :banana:

Yeah , we can mix this up some more .. What's the best oil to use with the used rings I just installed . :banana:

 

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MY FCR RIPS ON MY DRZ pretty much used all the specs on thumper talk, thanks guys, took my FCR off a 2001 YZ250F. 

Great it worked out for you , many fail .

How much did you pay for the used FCR ?

MY FCR RIPS ON MY DRZ pretty much used all the specs on thumper talk, thanks guys, took my FCR off a 2001 YZ250F. 

 

Yes, luck was on your side with an fcr of that vintage with unknown usage history....

Yes, luck was on your side with an fcr of that vintage with unknown usage history....

Possible low hour carb ............M8

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