Assembling top end of engine before sealing up the bottom

[Tim of DO THE TON]

Here's my situation.

I'm waiting on 2 oil seals for my bottom end (crank and countershaft).

Aside from that, I have everything I need to complete the engine build. Crank, endless cam chain, transmission are all in the case, just missing those two seals.

I'm thinking about putting a couple nuts on the bottom case, flipping the engine over and assembling the top end. Then turning it back over when I get the seals, pop off the bottom, put the seals in and Yamabond it shut.

Any reason to not do this? I can't think of anything. I wasn't going to torque the top end down till the bottom end was finished - just want to get things assembled and I have the weekend ahead of me.

The only thing I can think of is once the cam is on, the crank will be difficult to lift to get the seal on, but I'm pretty sure I'd be able to manage the one end of the crank to slide the seal in.

Thoughts? And out of curiosity, has anyone pulled the bottom end of an engine off while leaving the top end intact? In all my reading / forum perusing etc. I've not come across that scenario, say to replace seals, install a taller 5th gear etc.

 

[Take Warning15]

I've had the bottom off without opening the top. Totally regret it now, but at the time it worked out fine.

 

[Tim of DO THE TON]

Well that sounds like a story worth telling Were you trying to take a shortcut to a fix or did you drop something in you couldn't find later?

 

[hard_y_rd]

Do what you want. I would wait. I can't imagine wresting a tight cam chain and trying to get the crank to sit on the pins properly. It took me an hour just to get the crank to seat.

 

[Tim of DO THE TON]

The crank wouldn't be coming out or lifted at all - just enough to slip the seal onto.

Those bearing pins are a pain You did assemble the engine upside down right? I.e. putting the crank and transmission into the top 1/2 of the case?

 

[hard_y_rd]

Yes upside down. I guess you wouldn't have to move the crank much.

 

[Take Warning15]

Eh, my story is not that interesting, just frustrating for me. I had just bought the bike. It didn't run well but it did run. Before checking compression or very much at all, I just tore the bottom off to replace a few seals. Now that I have it running, I've got terrible compression and I'm pretty sure there is a bit of oil right where it shouldn't be. I guess I have a winter project at least.

 

[Curtis P]

Good things come to those who wait.....

I wouldn't try and short cut it.

 

[Tim of DO THE TON]

Yeah, I'll wait and be patient Have a CA95 engine here begging to be put together too anyhow.