Checking TDC

"Dave Plowman (News)" wrote in news: snipped-for-privacy@davenoise.co.uk:

Part No: DRA31491M TDC FINDER ? or the Part No: DRA51831 DIAL GAUGE .0005"- 1.00" (25.4mm) TRAVEL ? I can't really see you getting more accurate than that without going down the Starwars route. I'd ask if it is OK with the off centre plughole though. I would have thought it would be, as long as you rotate the piston nice and easy. For the dial guage you would need a clamp as well to hold it steady.

My feelings too. I was going to just break out the insulation on an old spark plug, and drill the base to accept some rod. But the pukka thing is now on order from Burton Power.

"Lin Chung" wrote in news:WMjMg.7743$ snipped-for-privacy@newsfe1-gui.ntli.net:

That is why a welding rod or similar works very well. The weight of it keeps it in place and all you have to see is when it reaches its zenith, then descends. No steadying hands needed. Rocking the piston up and down near it's uppermost travel will give you the TDC by eye. But, there are tools out there that do it, not necessarily better, but make the user feel better about the result.

True. But we arent looking for BDC and finding bdc to get tdc would be inaccurate.

What sort of angle are we talking here? If we are talking a fairly large angle from normal to the piston surface, say 30 degrees or more, then yes i can see it slopping a little - if you could hold the pencil radially still in the plug hole or use a roughy same diameter to plug item that is vastly reduced. But we arent talking about cranking the engine here - we are assuming you have some level of hand-eye co-ordination and are turning the engine very slowly with a spanner, not the starter! :-)

A few quid? Where? I want one, cheapest ive seen are 40-50.

Naturally, you pay for accuracy.

No-one is that curious that they would go to this effort and expense to find it without good reason lol. I can see how you may wish to set up valve timing very precisely. though this would require dyno time and you cant really do it from theory - its a tweak and test proceedure. Also, setting up ignition timing is best done relative as theoretical best values are not useful in real world. Again, someone wishing to get best timing would pop it on a dyno and adjust the EFI timing map while listening for knock and watching power output/EGTs. Theres no "correct" value. And depending on the system you're using for ignition control it is highly likely its set up with conservative timing and its margin of error is greater than yours with a timing light/plunger setup.

I'm honestly just curious as to why you think you need to know it so accurately, im geeky - this kinda thing fascinates me :-)

Or only actually use it to measure on the downstroke? Should be easy enough to remove and replace in exactly the same place by making sure threads are clean and marking where it tightens to by hand?

Yes - thought of that. Although a carefully read scale (if it has one) might just be accurate enough.

Basically, it's often said not to trust the markings. Mine is running at some 4 degrees static advance more than the marked setting for best results and I'd just like to know what the real static advance is. Definitively a geeky thing.

How about a grommet and a bit of bent wire?

Put an angle in the wire, and feed the bent down bit through the grommet. Press the grommet into the plug hole so it's a firm fit (might be worth putting some tape on the wire to prevent the grommet disappearing into the cylinder...).

With the end of the wire in the engine touching the piston, the other end will move through an arc - The longer that end the more movement per degree of engine rotation, so the easier to see by eye. Turn the engine till the visible end of the wire goes from rising to falling, turn back and forth till you're sure it's at tdc.

Probably wouldn't work, or be worth the time sorting out, but it's a (terrible?) idea :)

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Tunku saying something like:

Exactly. I think the OP is in tool-buying mode. Quite understandable; the new tool will be used once and be carefully put away in a drawer, safe in the knowledge that if it's needed, it's there.

Twenty years down the line the OP will discover it and remember why he bought it - then realise he's not used it since.

BTDTGTTS.

Well, it's only about a fiver which is ok even for a single use. My 'mechanical' feelings say a sloppy rod pushed down a larger plug hole and just resting at an angle anywhere on the piston crown is going to give a very approximate reading.

Quite likely.

"Dave Plowman (News)" wrote in news: snipped-for-privacy@davenoise.co.uk:

Heh, I've got a drawerful of such stuff in the garage, Colourtune anyone? Vernier calipers, spirit level, compression tester, TDC gauge (broken,remember to unscrew it before kicking the engine over) :-) , round wire feeler gauges etc ;-) A good angle grinder replaces the lot.

"No job's worth doing unless it needs a new tool."

That's my motto, that is.

I'll buy tools I *think* I will use if I think they're a bargain.;-)

Latest was today - a carpet kicker for 20 quid from Wimbledon Stadium Sunday market. Well made too.