1978 R100/7 Topend Overhaul

[rolyak]

Replace the gaskets and inspect the strainer (bell) for fatigue fractures. My R100S with 80K was severely fractured and one bolt was lying inside on the perforated plate. RePsycle had what they thought was a good used strainer but it also was fractured. These parts are cheap new!

Really enjoying your informative thread!
Tom

[20774]

Tom -

I wasn't going to disturb the pickup gasket...I figured I'd just remove one bolt and loctite it, then do the other. I suppose it would be a good idea to check it out since I don't plan on doing this again for another 30 years!

[20774]

I'm getting ready to fit the topend this weekend and got to thinking about the piston orientation. I know about the arrow on the crown...it must be facing the front of the bike. The piston has an offset wrist pin location relative to the top and bottom of the piston as it is installed on the rod...I did some measurements and confirmed that. Is there a left piston and a right piston?? At first blush, I would say no.

But, I got to looking at that. If I take one of the pistons and hold as if were the left piston, the arrow points to my left which is the front of the bike. If I hold that piston in that orientation, and walk around to the other side of the bike, the arrow now points to the back of the bike. So, to use it on the right side, I must rotate the piston 180 degrees. Fine, except that the location of the "short" side of the wrist pin has now also rotated 180 degrees. So, for example, the "short" side might be on the upper part of the piston the left side, but if I orient the piston for use on the right side, the "short" side of the piston is now on the bottom.

Am I goofed up on this? Is it all OK just as long as the arrow points to the front?

[20774]

I slept on things and may have figured out what needs to happen. I'm still unsure about the wrist pin offset, but will confirm that.

Here's a picture of the two new pistons. Basically it comes down to ensuring that the piston pockets are oriented correctly. My intake valve is 42mm while the exhaust valve is 40mm. On the left piston, it should be evident that the left pocket is smaller than the right. On the right pistion, the right pocket is smaller than the left. So, what I will do is installed the left piston on the left side so that the Siebenrock lettering is upright. The right piston will be installed on the right side, again so that Siebenrock is readable. I have to pick something, so that's what I'll choose.

The thing that is still confusing is that I could reversed the pistons from left side to right side and then rotate them 180 degrees and the valve pockets would be correct but the Siebenrock lettering would be upside down. That changes the location of the offset. That is what still has me wondering.

[Stan_R80/7]

The arrow on the front coincides with the smaller pocket for the 40mm exhaust valve. The pistons can be switched provided the arrow and smaller pocket coincides with the exhaust valve (front of engine). Otherwise, the intake valve will interfere with the smaller cut-out in the piston. Unless the wrist pin hole is off center, the letter orientation should not matter. Given the choice between having the lettering oriented as readable or upside down, I too would go with readable. Good luck!

[20774]

Stan -

Ted Porter confirms that it doesn't matter which side the pistons are installed on, only that the arrow must point forward. So, I'll do as I thought...install to the lettering is right-side up just so I have a point of reference for the future.

[DennisDarrow]

Boy oh boy oh boy those pistons are truly beautiful. Golly, one would be tempted just to sit one of them on the coffee table and just become one with them........lol..........YOU are doing fantastic Bud.....The arrow situation is totally standard and the way to go.........God bless .........Dennis

[20774]

Dennis -

That's the last time they'll look that clean! Maybe even the last time I even see them!!

[20774]

Made quite a bit of progress today...at least it's going back together! The new pistons and cylinders are on and the heads are on and have been torqued. I think I figured out that I'd never make it as a mechanic for a living! I'm kind of beat up today...I hope to post some pictures in the morning.

A big shout-out to Bill (aka jusbill) who came by and did more than kibbutz. He helped providing moral support, finding my tools, seeing things that I didn't see, and even getting a little dirty! Thanks!

The lesson I learned is "we don't need no stinkin' internal snap rings"! My thumbs will never be the same. Stay tuned....

[kentuvman]

Can't wait to see the thread that says "She started up and runs great"

Nice project you've got going, Kurt - may the force continue to be with you!

[20774]

Still recovering from yesterday...hard work! I didn't take as many pictures as I hoped...I must have been in the "zone".

The first thing was to put assembly lube on the exposed camshaft and then I lubed the new cam followers and slid them into their holes. I put a very thin film of Permatex Ultra Grey on the engine case and on the outboard side of the compression reducing gasket. I made sure there was no buildup of sealant around the top studs. The gasket was 0.66mm thick. I made sure the small o-rings were on the upper studs...they fit into small recesses on the bottom of the cylinders. Here's a not so good picture of the sealant on the case.

[20774]

Next was to assemble the pistons on the rod. This turned out to be a real challenge with the internal snap rings...my thumbs are still very sensitive today. This picture shows the snap ring I installed fairly easily with the piston in my lap. I installed each of these rings so that the gap was pointing to the engine. Then I positioned the piston so I could slide the wrist pin in and installed the opposite side ring...that was what took some doing. Also shown is the left side piston all installed on the rod.

[20774]

The rings were installed using the orientation noted by Oak in his topend book. He suggested (left side) the following locations for compression/nose/oil control rings at 4:30/10:30/1:30. The right side is the mirror of that.

I applied oil to the exterior part of the pushrod tube seal and around the OD of the pushrod tube and slide the seal onto the tube in the proper orientation (goofed on the right side and had reversed the direction of the seal; had to pull back and reverse the seal). Used a ring compressor to slide the cylinder on the piston but because of the style of ring compressor and the shape of the piston, the compressor was bottoming out and I couldn't get the oil ring to slide in. Bill noticed that. I found two smaller hose clamps and tied them together and created a ring compressor for the oil ring and got the cylinder all the way on. Before sliding home, I put some assembly lube on the skirts of the pistons. According to Ted Porter, the rest of the topend was dry except for some lube on the wrist pin.

This picture shows the cylinder all the way on with the head gasket installed in the proper orientation.

[20774]

The cylinder will only go on so far before the pushrod tube seals hit their holes. When I tried to put the head on and the rocker arms, there wasn't enough purchase on the head bolts to draw the assembly to the block. So, I removed the rocker arms and used a washer and head bolt on just the lower head bolts. It was important to draw the assembly down evenly and that can be done with the two lower nuts. Once it was within about 2-3mm of the engine case, I could install the pushrods, rocker arms, nuts and complete the drawdown of the assembly. I also had to back off the valve clearance adjusters to avoid putting any pressure on the rods.

Torquing went in stages to 10, 15, 20, and 25 ft-lbs. I used the sequence of bolts at the 2, 8, 4, 10, 6, 12 clock position. Here's a shot of the left side all done up. I'll go back and recheck torque soon to see if things have settled in any.

The right side went a little faster, but those darn snap rings were troublesome again. Things still to do are: reinstall oil pickup with new gaskets, remount oil pan and fill with oil, spin the engine to ensure oil flow to rockers, exhaust, carbs, and general cleanup. I need to wait for the tips of my thumbs to feel better!

[8ninety8]

I'm very envious of your very cool new hardware and the good work going on in your garage. Wish I could zip in those cylinders/pistons, but, it wouldn't be cost effective for my old bike. The fun part comes on start up. Easy as it goes, take plenty of time, congrats on the job.