F650 TDC Bolt FAQ

by Kristian #562, Simon (in Ireland), 15/07/2002
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 19 March 2007, by Winter #1935

TDC Bolt FAQs
- Why is there a separate FAQ for this silly little Bolt?
- What does the TDC bolt do, lock the cams in place? Where is it? Is it a part I have to buy or did I miss something?
- Where does it go?
- Won't Oil spill out all over the Place when I remove the Keeper Bolt?
- What is the BMW Part #?
- So is it REALLY NEEDED for the Valve Shim Check or Change?
- Is the TDC bolt absolutely necessary?
- Where can I buy a TDC Bolt?
- What is the Part No. of the TDC Bolt Location Crush Washer?
- It looks like a normal Bolt. Can't I just make one?
- Any Tips on how to get that TDC bolt in properly?
Making a TDC bolt

For other related FAQs:

TDC Bolt FAQs

Why is there a separate FAQ for this silly little Bolt?

Because there has been some healthy debate over whether it is REALLY needed.

What does the TDC bolt do, lock the cams in place? Where is it? Is it a part I have to buy or did I miss something?

The TDC bolt is a Bolt you can buy from BMW (or make) that screws into the crankcase (Circled Red) to keep the Crankshaft (Circled Green) from turning. There's also a bolt (Allen head) under a plastic cap on the right center of the engine that is used to turn the engine over (with the sparkplug out) to position the engine for the valve clearance check. The Bolt that locks the engine in place is used whenever you want to do that, as in adjusting the valves. You don't REALLY need it, you can do the same thing by putting the bike in gear. (and you can't forget it that way when you go to start the engine and realise it won't turn over because the bolt is still in !!) It's used when you check your Valve Shim Clearances (Classic) or change your Valve Shims (Classic), change your Valve Shims (GS/Dakar). Here is a picture of an Original TDC Bolt

Where does it go?

Into the LHS Engine casing, For a picture of where the TDC Bolt goes see here: TDC Bolt Insert Location (Classic, GS). You must take out that Shiny Silver Keeper Bolt First).

Won't Oil spill out all over the Place when I remove the Keeper Bolt?

Well a little Oil comes out, but it's a very small flow and if you are reasonably quick putting the TDC Bolt.

What is the BMW Part #?

90 88 6 116 570 TDC Crank Stop Bolt. (Classic. GS Unknown so far). It costs about US$1.50, IF they have it.

So is it REALLY NEEDED for the Valve Shim Check or Change?

For the Valve Shim CHECK, it's useful practice for the Valve Shim CHANGE but no, it's not absolutely necessary for either, you can get by without it. If you are a beginner, get the bolt, if for nothing else than for peace of mind. The point is it's cheap and takes 30 seconds to install.
Valve Shim CHECK: If you're confident you have the Gear Wheel Marks lined up at TDC, you can simply measure the Valve Clearances without the Bolt. Just don't move the Rear Wheel. Put the Bike IN GEAR, this helps "lock it" while you're measuring your clearances. Note that with the Bolt in you KNOW you are always measuring the Clearances at the same Crank Position, but the timing marks are just as good
Valve Shim CHANGE: Tricky to answer, but it really depends on your level of confidence. Quite a few have done without it, so again it is NOT imperative. If you're doing the Valve Shim Change for the first time, buy or make the bolt. It won't kill you.

Is the TDC bolt absolutely necessary?

The TDC bolt, is not ABSOLUTELY necessary to check the clearances. Just make sure the two marks on the cam gears point at each other, like in the picture. But instead of using that bolt to lock the engine, it's just as easy to zip tie the chain to the cam gears per the FAQ, this will accomplish the same thing. That is, if you check the clearances and find they need to be adjusted.

Where can I buy a TDC Bolt?

You should be able to buy the TDC bolt from your dealer for about US$1.50.

What is the Part No. of the TDC Bolt Location Crush Washer?

It is an A8x13 copper washer available at a lot of good auto Shops. Aluminium Works OK too. BMW Part No. 11 11 2 343 010.

It looks like a normal Bolt. Can't I just make one?

You can make one by grinding a more or less rounded end on a bolt that is about 25mm long or longer and fits in the hole. There is a groove in the flywheel into which the screw fits, locking the flywheel in place. The reason you want to round the tip (or at least grind it to more of a point, is so that it fits the groove in the crank flywheel. You see the bit with the green oval in the above photo. That is the groove in the flywheel. You see the part in the red circle? That is the tip of the dollar and a half bolt. If you DON'T sharpen it, if it has a standard FLAT end, then it will not find the groove.

Any Tips on how to get that TDC bolt in properly?

Take an 8mm bolt about two inches (50 mm) long and grind a dull point on it. Remove the bolt from the left side of the motor that fills the hole into which the TDC bolt goes. Screw your homemade TDC bolt in there until it JUST touches, then back if off a turn.
Remove a spark plug. Stick a screwdriver down the hole. Rock the crank using and Allen key through the removed plug in middle of the alternator cover on the right side. Turn the key SLIGHTLY and see if the screw driver rises. If not turn it the other way. While GUIDING THE SCREWDRIVER, turn the key so that it rises, up to the point where it starts to fall. Rock the key to try to find TDC.
Screw your TDC bolt in until it touches. Back it off about 1/8 turn. Try to move the crank. If it moves more than a skosh it isn't on TDC. Find TDC.
The CRANK has only one TDC. The CAMS run at half crank speed. The motor doesn't care if the cams are on overlap or compression. You want to assemble the motor on compression (all valves closed) because it is easier to do. With the crank on TDC the lines on the two cam sprockets should point STRAIGHT at each other. And the "extra hole" in the two cam sprockets should both be pointing up (or down). If you are worried about cam chain slack when trying to figure out if the lines are pointing at each other, put the carrier back together and reinstall the tensioner. All doubt will be removed. Flash #412 (CO)

Making a TDC bolt

Flash notes the the TDC bolt on the Classic is the same as the fuel tank rear bolt on the Classic, so you can use that to make one and always KNOW exactly where it is.

I am posting a picture of the TDC bolt I just got from BMW because it is not rounded as the one in the FAQ. I tried it and it works just fine, so the rounding is not necessary if you decide to build your own. gim

CLASSIC: M8x1.25 bolt 40-50 in Length.

GS/Dakar: M8x1.25 bolt 40-50 in Length.

(Reports are that some Classics have needed an M8x1.0 bolt. The reason/bike years are not known. But hey, they are cheap to make, so perhaps buy BOTH and check it in the hole before making it).
(M8 = 8mm Bolt Diameter, 1.25 (1.0) = thread pitch)
There is a plug bolt on the left lower side of the engine that you remove and insert the TDC bolt which goes in a slot in the crankshaft, locking the engine for camshaft removal/installation. Buy an M8x1.25 bolt. (M8 = 8mm diameter bolt, 1.25 = thread pitch) about 40-50mm long at the store AND get a nut that fits it. Screw the nut on the bolt and make it look like the picture in le FAQ. (i.e. a 45 degree angle not to a point on the end) using the bench grinder. With the point ground on the bolt remove the nut from the bolt (you'll need to clamp the head of the bolt in a vice and turn the nut off with a wrench) Grinding messes up the threads on the end and running the nut back and forth restores them. So make sure the nut is on before you start grinding!
The TDC bolt for the CLASSIC is an M8x1.0 bolt. M8 = 8mm diameter bolt x1.0=1 thread per 1mm about 40-50mm long. The end needs to be rounded off to fit the detente in the flywheel. I suggest getting one from Bob's BMW, they'll mail it to you within a week. Take it to the dealer who said "you couldn't have one" and show him what it is and tell him who you purchased it from. That'll make him feel special. Your dealer doesn't want you to have that "special tool" because he doesn't want you to do your valves because he wants you to spend the money at his place to have his monkeys strip your threads and not re-torque your head. The hardest part about checking valve clearances (save from actually replacing a shim) is putting all the bodywork back on.
Note that reports are the Classic Bolt is NOT the same thread pitch as the GS Bolt. Apparently, the Classic Bolt is M8 X 1 about 40mm long, although my Classic Bolt fits my GS. (ed.)
Here is an Original TDC Bolt for comparison.
Rand #1111 supplied these nifty photos of a way to do it.
Feedback on the Right Size: By the way the FAQ's says my TDC bolt is 8mm x 1.0mm. It is not. It is 8mm x 1.25mm which is more normal. On both my 99' and my wife's 97' the TDC bolt is 8mm x 1.25 mm. So there. XtreemLEE