Rebuild the bottom end or just leave it?

[D6lc]

I have just purchased an 85 RZ350, it’s got just over 9k miles and it is reasonable condition overall, good news is that its original. The bike started and idled ok, but I haven’t ridden it due to other issues with it.

I’m currently stripping the bike to clean it up, my question related to the engine.

Its going to be out of the bike and I will strip the top end to check it out and clean it up & paint various parts.

I wasn’t planning on stripping the cases, but was just thinking that the bike is 30 yrs old and hasn’t ever been rebuilt so the oil seals are all original, and I guess pretty hard by now!
With the engine out of the chassis, should I just bite the bullet and split the cases to replace the oil seals & gear change seals ? if your splitting cases anything else to replace whilst in there?, clearly I’ll inspect everything and replace what needed.

Or would you advise just to rebuild the top end and leave the cases alone?

[xkabooomx]

Definitely replace the seals, and coolant o-ring. Also check the crank for tolerance. I'd also give the shift forks a good look over also. And of course, check everything while apart. Crank seals are a must, unless you want airleaks/transmission oil consumption.

[pushstartrearset]

Always best to do the full motor. That being said. We have and 84 and 85 RZ350, where i hate to admit it, but haven't done the bottom end on either yet. I think yamaha hit a home run w/ the RZs, very durable and reliable bikes. We bought the 84 in 2010? w/ 3k miles on it. fixed the minor issues and ran it. Bike still runs at over 20k, but now needs a full rebuild. The 85, we've dogged bad and it's held up (wiseco pistons)...30k miles! <===motor is badly in need of rebuild.

You couldn't do this w/ the aircooled motors. if you do plan to do this be prepared as if the seals do go, you'll be spending twice the money. I've been lucky so far, but think mainly yamaha built a better motor than the aircooled obviously. Our 84 looked was stored in a forest location,so you can imagine the moisture problems. the plus side is ORIGINAL pistons...probably explains the durability.

Like was said many times, use only OEM yamaha seals. If you are in question of a kit, just buy them separately from a yamaha parts dealer. Might be expensive, but you know you aren't getting inferior stuff. PS--> check the springs on the seals...if rusted or damaged, throw away (don't bother) and keep buying until you get a good one, even if it is new!. I've seen seals, especially with bad springs that i've had to throw out.

[seahorse]

+ 3 split
You can also buy replacement gearbox bearings and the odd
Replaceable bush including a clutch bush fairly cheaply
Iv used fast from the past to purchase my bearings on several builds
Rebuilding the gearbox is just a bonus if you have the crank out
I'd be concentrating on the condition of the crank and considering the mileage
Have it tested
time spent doing things the right way etc

[JonW]

+4