/5 timing

[Jean]

With my NEW PARTS, timing was OK with plate in a more normal position, to answer the first question, of native/5. It was ONLY when my chain (and small sprocket) was very worn that the slot-filing was necessary. Necessary at that moment because I had to get the new parts and find the time to actually DO the repairs, not easily arranged during those years!
Garnet's comment is something to ponder, too. That could be resolved by checking part numbers using numbers from MAX-parts fisch perhaps (?)
N/5...you haven't mentioned the "S" mark at all. Static timing ought to be set up with the "S" mark in the middle of the window.
You said: "I find that the "F" mark has gone way past the window at 3500+ rpm". Reading in my many references, I find the "F" mark should be in the window at about 2600 rpm, so disappearing at 3500 rpm isn't as bad a problem as you might think. I didn't react to THIS at first because 3500 rpm IS the advanced-timing speed for the bike I use the most.
Back to the "S" mark. Are you setting idle speed to 600-750 or 800-1100? A different way to ask this is, can you see the "S" mark when the engine is idling??
The slower idle is for the pre-78 years and the higher idle is for the later ones. IF you had a sprocket for a later engine and the points plate, etc for the earlier engine, you would probably run out of slot trying to get things timed.

[Deleted User 72]

Did you get the correct sprockets? In 78 they advanced the cam timing by 6 degrees. I believe they did that by moving the key slot in the cam sprocket. If you got a 78 cam sprocket then maybe that's the isue.

You had me worried there for a moment, Garnet.

According to Max's fiche I got the earlier (correct) sprocket. Had I known the newer one was 1/3 the price I might've got the later one and filed the timing plate slots. Which it looks like I'll be doing anyway.

Jean,

There is an "S" mark?






Just kidding... I didn't mention the "S" mark because it never showed. As I said earlier, with the engine at idle I can just see the spot near the "F" mark down below the window. At that position the "S" mark was not visible. When setting up I usually time the engine initially at rest with a meter or light on the points with the "S" mark centered.

Unless someone saves me, I guess I'll file those slots, someday, if it ever starts running crappy or pinging.

[Jean]

And your IDLE speed?
If you set-up at static for the "S" in the window, it OUGHT to be in the window at idle, IF your idle speed is in the limits listed.

[Deleted User 72]

I don't know the exact idle speed, but I know it is no more than 1000 rpm. I have not set the static timing on this bike for a while, as it is already running (pretty good, too.) I think it would be a good idea to check now and see where the points actually open.

I won't get to that until this weekend at the earliest. I'll post what I find here.

[Jean]

OK.
My R75/5 confounded me when I first got it as I didn't realize how low the correct idle speed ought to be since I had only experience with the 77-78 R100 series. I used a little light with wires and clips to set the static timing using the "S" in the window, and with the engine hot, set the idle to around 700. (That tiny tach isn't much good....).
NOW the marks were in the right place. BTW, I've not had to mess with the points plate, etc to get the timing "in" on this bike. It seems to be a lot easier to use the light, set it static at "S", and then check idle and running conditions.

You called your bike an R90/5, 1973. Is this an R75/5 with a "90" top-end (a HOT combo teamed with a pair of 38-Mikunis) or a REAL R90/5? I thought the R90 series started with the /6 series.

[Deleted User 72]

Yes, that little tach is not much good, at idle especially. The idle I have set now has the alt light glowing pretty good, thus my confidence that it is under 1k rpm. My ears corroborate this.

I had a problem with this bike after installing hard valve seats. The intake valve on the right side was just barely touching the piston, on deceleration only. I swapped everything swappable from left to right to try to isolate the problem. I took the top end apart at least 12 times (I quit counting) with no resolution. It was during this episode that I replaced the timing chain. I posted a thread on Boxerworks about this before the switch to this new software. The thread subject was "Tink", I think. Vanzen saved my sanity with some email exchanges on the subject. Thanks, Rob.

I finally gave up and installed the 900cc components (heads & cyls) I had been collecting, whereupon the valve no longer touched the piston. So,.....R90/5. I know, too much information.

[Jean]

I just HATE it when the valve "touches" the top of the piston. Talk about ZERO clearance!!

[Deleted User 72]

FYI

Checking the static timing with a 12V bulb grounded through the points, the bulb goes out when the "S" mark is ~1/4 " above the middle of the window (advanced). This is with the points plate fully retarded.

I am going to file the slots in the points plate longer just so I can experiment with the timing to see if I can get it closer to spec. After all, there is no real harm in opening up those slots.

[Jean]

It sure sounds like the chain is one tooth off on the cam sproket.
Not good news as it is a PITA to get to!!
Unfortunately, it also suggests your valve timing is a little bit off...

[Deleted User 72]

I agree, and it might explain how the intake could touch the piston by opening too soon on the 750cc setup. But the cam and crank are both marked with a spot to be aligned on assembly, as they carefully were. And they were aligned with the old chain as well, which ran in the bike for who knows how long before I got it. Nor do I think that the motor would start so easily and run so well with timing off by a tooth. Maybe I am wrong, but things will have to get much worse than they are before I tear that baby back down that far.