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Discussion Starter #1 (Edited)
Hi, I am trying to find TDC (or rather 38 before TDC) on my early '68 T120 (installing Boyer ignition) and would welcome any advice anyone can give :smile2:

The bike doesn't have the cam timing plug behind the cylinders that my '67 has, I believe the place to check TDC on an early '68 is down at the front bottom of the crank case although the only comment I have found to confirm this was....

"Starting with Engine #DU66246, the threaded timing hole (used to locate TDC) that was behind the cylinders was moved to a location below the front engine mount. The flywheel now had 2 notches, one at TDC and one at 38-degrees BTDC (the standard advance at the time). But to make it more convenient to time the engine, an entirely new system was employed as of Engine #DU83021, which included a new primary cover with removable inspection plate over the alternator stator and corresponding timing marks on the stator & the primary cover. Ultimately, the threaded inspection hole in front was turned into a drain plug & the timing plug moved back to its original location, behind the cylinder block."

...found at http://www.classic-british-motorcycles.com/1968-triumph-bonneville.html

My engine number is DU67XXXX so I'm hopeful that if I can get the plug out (currently stuck solid) and put the TDC tool in there I should be able to push upwards and feel both TDC and 38 degree notches. It does look awfully like the location a drain plug might go so am worried that I may be getting a oily bath !

I've attached a photo in case that helps save me an oily face. (apologies I can't get the image to load the right way, even if I rotate in on my PC first it always appears upside down in the post!)

thanks
Andy
 

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I have no personal experience of a timing plug in this position - however it certainly fits the description - i cant see it being a drain plug as its not at the lowest point in the crank case - use s small gas blowgun to heat the plug and surrounding area - maybe make a tool to fit the slot tightly out of a piece of flat steel bar
 

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Hi Andy,
I'm in exactly the same position as you with exactly the same bike model and year. That plug at the front is definitely the place for the TDC tool. My bike came as several boxes of bits so I was able to see the crank - my one has only one notch in it - that's for TDC location. If yours is the same, you'll have to get the crank lined up at TDC, then use a degree wheel on the alternator rotor to find the 38 degree BTDC point. The easiest way is to take off the primary cover to get better working room but I've made up a smaller degree wheel so that I can use it through the primary cover's inspection plate.

That inspection plug isn't the correct one. The correct one has a hex head that sits higher than the crankcase - that means that you can easily get a socket or box (tube) spanner onto it. Once you get the current plug out, it might be worth putting in the correct one so that it's easier to remove next time. The part number is 70-4706 (E4706 in old terms). It needs to be fitted with a fibre washer under the head.

By the way, if you have a 'replica' Lucas rotor (I have one of the new Lucas badged/boxed ones - Wassel, I think), the engraved TDC line on the rotor that is supposed to line up with the factory pointer tool when the tool is inserted into the special hole in the primary cover, doesn't actually line up properly; it's a couple of degrees out. To get over that problem, I got the pistons at true TDC and scribed a new line on the rotor to line it up with the pointer. If your rotor isn't an original, AND you are using the factory pointer tool, you might want to check that. Alternatively, if you're not using the factory pointer tool but instead are using your own home-made pointer, that won't be an issue as you can simply move the pointer to align it with the scribed line and all will be well.

Hope that helps.

Good luck with the Boyer - I've just fitted mine and the engine is running really nicely at low rpm - good tickover. As it's not yet been strobed it's not yet ready to ride - I also don't yet have a fuel tank - but that's a minor issue! :wink2:

Regards
Tony
 

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You don't really need the hole or a notch in the crank to find TDC. And knowing how to do this will help you with future engine work.

Pull the plugs out and run the piston on the left side up to TDC by peering thru the plug hole.

Pull the primary cover off and mount a degree wheel. You can find them on-line for easy download. Size it, print it out and paste it to a piece of cardboard or sheet metal. Then mount it to the crank. Make a pointer from a piece of wire and mount it on an alt stud.

Now, put a piece of dowel or similar in the plug hole so it rests on the piston. Put a pair of vise-grips on the crank nut. Yes vise-grips because the alt magnetism will try to move the crank and a wrench is too sloppy a fit to control this. With one hand on the piece of dowel and the other on the vise-grips turn the crank back and forth slightly going over TDC and back. There is a dead zone where the dowel will not move. Try to feel when it just stops on BTDC and when it just starts on AFTDC. Watch the degree wheel and measure how much crank rotation is between those two points. Now turn the crank to the point between those two points and that is exact TDC. Set your degree wheel to TDC or zero on your pointer and you are ready to go. Always good to recheck again to make sure you got it right.

If you have a dial indicator, it is even easier as you simply measure a point before and after TDC in thousandths and then set the degree wheel that way.

Check your factory marks on the stator if you have them. If not, there is room inside the primary to make a degree plate and mount it to the alt studs. I did this on my '66 which has no markings. A simple mark on the rotor is used to read the degree plate. My resto thread has pics of this and an explanation. I've attached a pic here for convenience.
 

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Discussion Starter #5
Thanks all!

That bolt is just not coming out for me at the moment though I did order the correct replacement for when I finally get it out, thanks for the recommendation Tony.

Now have the primary cover off and I've got a timing wheel, magnet and TDC tool ready to go at timing it later tonight.

I also took Snakeoils advice and have made up a (poor) replica of the degree plate which looks like a great idea to me.
 

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There is another way to find 38° before TDC and is discrribed to detail in Wes Whites video that can be purchased from Lowbrow.

I can't remeber the exact process but has to do with a degree wheel a home made pointer and some math. The TDC tool for pre 69 engines will screw into the spark plug hole and when brought up to it's highest point you are at TDC however you can have up to 7° of piston float. Thats where the degree wheel and math comes in.
 

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You are fitting a Boyer.

Bikes after DU66245 should have a timing mark on the alternator rotor.

You only need to get the initial timing set well enough to get the bike started, your real work is to time it using a strobe at full advance, using the timing mark. I'm not sure at what revs a Triumph Boyer reaches full advance, but best to set on the full advance mark when you can see that the Boyer has advanced the timing as far as it can go. This will probably be above 3000 revs.

I hope this helps
 

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Timing 68 T120R

I have the same bike as you and Tony. As Tony indicated the time plug is in the front lower crankcase. I only have one notch in the crank and it is at 38 degree BTDC. On my bike this lines up with the timing mark on the rotor.

Regards, Steve
 

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There is another way to find 38° before TDC and is discrribed to detail in Wes Whites video that can be purchased from Lowbrow.

I can't remeber the exact process but has to do with a degree wheel a home made pointer and some math. The TDC tool for pre 69 engines will screw into the spark plug hole and when brought up to it's highest point you are at TDC however you can have up to 7° of piston float. Thats where the degree wheel and math comes in.
You use a piston stop, and a degree wheel....The procedure is better described on the many cam shaft company sites on the Internet...This is the only way to find TDC accurately....
Use caution with a piston stop because it is possible for an intake valve to foul the tool and bend the valve depending on types of cams and cam timing...Ask me how I know this....:surprise:
For the record, I have checked TDC on several Triumphs and found the crankshaft TDC and 38 degree advanced slots to be right on... The primary cover pointer was within a degree or less...
 

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Came across this thread and was jazzed to find out that there was in fact a hole to find TDC on the flywheel (or 38 BTDC according to Service Bulletin 294) on my early 68 engine (DU681XX). However, when I went to pull the plug, I did, in fact get a fountain of oil. I didn't wait around to see if it was only a little bit though before i screwed back in.
 

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Hi lovatomi, Very sorry I didn't look close enough at your rotor photo. You have early version primary cover with access plate, but no timing pointer.

You need special tool D2014 (60-2014). Screw onto holes for the access cover. Ends up with a mark about at 5 o'clock that will line up with 38b mark on rotor. Se section B32 in 650 manual. I don't own this tool, I have never used this tool. The '68 I've worked on all had pointers built onto primary cover like in photo of my bike on your prior post.

Tool has C & B marks. 650 uses B mark. (C mark is for 500cc motor). So use B mark.


The plug you have is the timing plug & if crank is original to your markI early '68 case it will be 38b with TDC tool in slot in crank. Looks like you have the top of the 3 conditions shown in manual section B31. Expect about 100cc ish oil to drain out. Good plan to put sealant on washer also. They seem to like to seep.

So looking like you'll need both TDC tool & the timing pointer ring tool. Ain't Triumph ownership great! Actually it is. You just need a lot of tools. TDC tool to verify 38b & the pointer ring to know where it is on primary.

Seriously, once you get all the tools you need this stuff isn't too hard with a little practice.

Regarding degree wheel & piston stop. I've also had experience with 3/8 diameter piston stop hitting intake valve. You must use 1/4" stop stem to clear intake valve. Grind the 3/8 stop thinner if your stem isn't 1/4". IN EVERY CASE LOOK IN PLUG HOLE, TURN MOTOR UNTIL INTAKE VALVE FULLY OPEN. GENTLY INSTALL TDC STEM TO VERIFY IT ACTUALLY CLEARS INTAKE VALVE.

No reason to use piston stop or degree wheel if have the TDC tool & D2014.
Don
 

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