Hep with engine rebuild

G-Man · Post by **G-Man** » Sat Nov 12, 2011 3:12 am

Hi Skisurf

Essentially, now you have the motor in pieces you just have to inspect the parts for wear and tear then clean and replace or refurbish the parts to a good standard before re-assembling.

The valves should contact the valve seats to create an all-round seal and this is done by 'lapping' the valves into the head with a grinding paste. A fresh set of valve springs might be useful if the engine has done a high mileage.

As for the rings and cylinder bore, their job (among other things) is to provide a good seal as they slide together. Wear or damage to either will affect the compression. If the bore has worn beyond limits, you may need to get this re-bored to a larger size.

I'm going to send you (via PM) a good motorcycle restoration text which is very educational and helpful for understanding all of the issues.

Good luck!

G

skisurf · Post by **skisurf** » Sat Nov 12, 2011 3:08 pm

Here's a look at the cylinder and pistons. Everything looks normal to me but again, I'm a rookie. The rings are pretty loose, is that normal? There was also a little bit of oil that leaked out when I pulled the cylinder. Would I assume that means everything in there is sealed?

Next step, I'm going to lap the valves. Fill the dome and see if it leaks.

skisurf · Post by **skisurf** » Sat Nov 12, 2011 9:17 pm

Update: Lapped all the valves. Did a leak down test without the springs and both exhaust valves leaked, the right (side w/ low compression) leaked like a siv. I literally lapped the right side valve like 20+ times and only half the valve will clean. And it sticks pretty bad once pushed all the way in. I have to use pressure to get it back out.

I bought a couple of 'like new' exhaust valves on ebay just in case. I put one in the right side just to see and it barely leaked at all.

Couple questions.

1) Can I (should I) use the 'like new' valves as is or do I need to do anything else?

2) Do I need to cut the valve seats at this point?

3) Based on a Youtube video I decided to test the leak w/o the springs. Is this the correct way?

Attached a couple more pictures. You'll see how only half the right side valve would clean.

G-Man · Post by **G-Man** » Sun Nov 13, 2011 2:22 am

Sounds like your right side exhaust valve is bent. I would use the replacement.

G

davomoto · Post by **davomoto** » Mon Nov 14, 2011 9:51 am

I would take the head and barrel to a machinist. Have him cut the seats, and measure the bore and pistons. If the bore checks out, install new rings.

Davo

skisurf · Post by **skisurf** » Wed Nov 16, 2011 5:27 pm

First of all. Thank you everyone for your help.

A member sent me a PM and suggested I check to see if the valve that wasn't seating is bent. Threw it in the drill and sure enough. Replaced it with one of the valves I'd purchased. Put everything back together last weekend. I assembled the engine only to realize I'd forgot to set the timing. I had a lot of fun when I heard the dreaded clink clink clink as I was taking the cam chain clip out. I thought about just giving up altogether for a minute...

Today I cleaned the carbs and finished putting most of the bike back together. Fired up first kick. Sounds good, idles strong. About to test compression. Knock on wood!

Thanks again. I learned a ton while doing this.

skisurf · Post by **skisurf** » Wed Nov 16, 2011 5:55 pm

Right: 120
Left: 105

Is that decent?

Forgot what left was before but the right was low, like 40ish.