• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR4/4A No Marks on Timing Gear

Share this page

KVH

KVH

Darth Vader
Silver
Country flag
Offline
I'll follow the manual carefully, but I'm surprised to see no markings while on my rebuild. Did all new, stock TR4 models have marks on the timing gear?

I assume I can only mark that gear after full reassemble with the head on and valve clearances measured, correct?
 
I've never seen one without marks but that certainly doesn't mean they don't exist. It's usually a scribed line on the face of the cam gear and on a tooth of the crank gear. You won't need the head on to time the cam but you will need to turn the engine so make sure the liners bolted down. Macy's garage has a tech paper on the timing process.
https://macysgarage.com/cam degree.htm
Tom
 
Instead of a mark on the fan pulley, look for a hole. I have seen a few that that was the timing TDC at the arrow.
 
Are you using new gears or the original? I understand that some (at least) of the originals had marks, but most, including new parts, do not. That's why there is a long, complicated, inaccurate method described in the shop manual.

The whole point of the timing is to set the crank at tdc, and the camshaft precisely halfway between the closing of one valve and the opening of the other at the end of the exhaust stroke. THEN, you have to select the timing gear orientation so the chain fits precisely. It is decidedly a royal pain you-know-where, but that's what we have to deal with.

Here is what I did: http://www.nonlintec.com/tr4a/engine/#timing. I didn't have the head on, and I think it's easier without it in place.
 
Cam timing is a lot of fun when you don't have marks and haven't done it before. I did a lot of reading "The whole point of the timing is to set the crank at tdc, and the camshaft precisely halfway between the closing of one valve and the opening of the other" is my understanding of the essence of it (at least for a TR, I understand not all cams are engineered that way). As to how you measure, there are dozens if not hundreds of methods for measuring lift. I read a bunch of them and ended up doing what made sense to me. I know a friend of mine did an engine shortly after me, and the way he was doing it made no sense to me but it did to him.
 
Last edited:
While working with a mechanic on the engine rebuild, i recall that we transferred the marks from the old gears the new ones. That at least got us close. Which is a good lesson to remember to mark the old gears before you remove them, assuming that they did not have any marks.
 
Some cam timing is given at max lift for #1 cylinder intake valve. Not too difficult to do with a good TDC wheel and dial indicator. As absolute max lift is difficult to measure you measure maybe 10 thousand before and after max lift and split the difference on the TDC wheel.
 
Stock TR4 cam, as well as the majority of aftermarket cams, are designed as Greg said. 0 cam advance is when both valves on #4 are open the same amount (exhaust closing and intake opening); which means #1 is ready to fire.

The stock cam sprocket should give you 4 possibilities within each tooth, and each tooth is about 16 degrees, so it can be adjusted in 4 degree steps. If you can't hit zero exactly, its better to be a bit advanced, since the chain will stretch a bit in operation.

But some aftermarket sprockets are apparently not drilled right, so you can't get the 4 degree steps by flipping it and/or using the other pair of holes.
 
Holy moly am I confused. I've read all the procedures above and in the links. I need a rest. Tools to make, degree wheels to find and set up, pointers to fix, 1/4 tooth flips to figure. I'm just an aging neurotic guy fiddling with a car for criminy.
 
If you are more of a hands on type learner like me it will probably be less daunting if you just start working on it, get a degree wheel, determine TDC, and go from there. If you have a mechanically minded buddy have them come over and double check everything before you button it up.
 
Sorry, sometimes that's what it takes. You can actually get by without the degree wheel; and a pointer can be as easy as a piece of coat hangar wire wrapped around a handy bolt. You could even get by without that, if you find TDC at the flywheel.
You might even get lucky and find the timing marks on the flywheel (or not).

If not, make up a piston stop, which can be as simple as a piece of flat iron drilled to fit over a pair of head studs, and a bolt in the middle. Install the stop over #1, turn the crank one direction until the piston hits the stop. Make a mark on the back of the block, and a matching mark on the flywheel. Now turn the crank the other direction until the piston comes up against the stop again. Make another mark on the flywheel matching the mark on the block. Measure between the two marks on the flywheel (or count teeth if you take partial teeth into account), make a third mark exactly halfway between the first two. That's TDC.

After that, the method given in the workshop manual for setting valve timing without the marks should work fine. It does need the head and the valve train to #4 in place; but you can just set the head down over the studs, install two pushrods (for #4) and tighten down the rocker shaft.

Or, wait until you get to that point in building the engine, either way.

It's not really important that you understand the following, so ignore it if you like. Just a bit of theory on why the "on balance" method works:

The TR4 cam should have the intake valve opening 17 degrees before TDC; while the exhaust valve closes 17 degrees after TDC. The lobes are symmetrical, which means both valves move the same distance in that 17 degrees. So, we're checking for when that is the case (both having moved the same distance), which is 0 degrees from the cam's point of view. Set that to match 0 degrees (TDC) on the crankshaft and Robert's your near relative (or something like that).
 
As for degree wheels, if you don't want to buy one there are templates online that you can download and print out... including mine.

See the link below, search for "degreewheel", download it and print it as large as you can. I have one I printed on 11x17 paper which I bonded to a 1/4" thick sheet of MDF. Once the glue was dried cut out the center and the perimeter. I sprayed it (both sides and circumference) with clear acrylic so it wouldn't get ruined too quickly.

https://sites.google.com/site/purlawson/home/files
 
Re degree wheel. I aagree with Doug, the bigger the better.
 
Thanks everyone. I’m on it now. I made a 9 inch degree wheel. Hopefully not too small. I think I need a new timing gear. Mine appears generally good but I’m seeing four slight tooth abrasions approaching tiny chips or nicks. All on the side of the teeth, Forget it or buy a new gear?
 
Tough call, IMO. Can you post a photo?

If new ones were always perfect, I'd say replace it. But new ones aren't always perfect, and sometimes it's hard to tell the difference. This happened to a friend's Stag, with less than 10,000 miles on new chains and sprockets
hOuuE4p.jpg


Another point, I was always taught to replace the sprockets and chain as a set. They wear in together, mating a new part with an old one causes the new part to wear more rapidly until it matches the old one.
 
And what about making a dummy tappet? Is that really necessary? shouldn't the pushrods be accurate enough or is it best to adjust everything with the head off?
 
KVH said:
Are valves 1 and 2 in balance at exactly the same time as valves 7 and 8?
Click to expand...
No; they are exactly opposite on the camshaft. Both valves partially open means the piston should be at TDC between the exhaust and compression stroke. When #1 is at TDC between exhaust and intake, #4 is at TDC between compression and power (IOW ready to fire) with both valves fully closed.

No need for a dummy tappet as long as you have one that moves easily in the bore. Sometimes they are a bit stiff on new engines, but that's not likely to be a problem on a TR :smile:
 
Can I please get an explanation again of the difference between the compression and power strokes and the intake and exhaust valve operation? I know that sounds so basic. I also know it’s been explained before. But somehow I just don’t quite get it—or why the shop manual says to measure valves 7 and 8 and yet the Macy’s process measures valves 1 and 2. Apologies in advance.
 
Back
Top