How I Set my TDC This Afternoon...........

[72BLUE]

Hope this is useful to some folks!

I had read here on the forum that the crank timing marker was not always accurate, so thought I would check mine out. I had also read that it was difficult to gauge TDC of no 2 piston, so in lateral thinking mode, decided to try out my cheapo endoscope camera thing that I got off the bay a while back and then try with a simple DIY 'U' tube of water, which I think might be called a manometer?

Both worked remarkably well :-)

METHOD 1: Endoscope and Laptop

IMG_2117.jpgIMG_2119.jpg

I marked the top of the lense and wire with tippex (it is easy to accidentally rotate the lense and therefore image visible on laptop) and held the lense in place, in no 2 spark plug hole, with a lump of blu-tack. It is possible to get a view of both inlet and exhaust valve and the top of the piston all at the same time.

As the crank is rotated the piston travel can easily be seen. The trick is to look closely at an appropriate mark on the piston crown as it rises and falls in relation to the bottom edge of the image window on the laptop. I therefore used the bottom horizontal edge of the image window as a sort of datum line.

I was surprised how quickly the vertical movement of the piston changed to from up to down btw, I had read that there was a noticable period of crank rotation when no movement occurs, from my experience here, there is hardly any 'slack' period.

Photos of No2 Piston and Valves Captured off Laptop:

Picture 001.jpgPicture 004.jpgPicture 005.jpg


Second (U tube) method in next post due to photo limits.........

Cheers
Keith

[72BLUE]

METHOD 2: U Tube

This also worked well, I did it on a cold engine, so vacuum did not hold for long, but by rotating the crank back and forth around what you THINK is TDC on the crank marker, it will tell you if the piston is moving up or down by the direction that the water moves in the tube.

If the right side of the tube moves up, the piston is moving up. If water moves up on left side of tube, piston is moving down.

After a little fiddling with rotating the crank and getting the feel of how the gauge responds, it is remarkably accurate! The water does not hold its new pressurised position for long, but you get a clear indication of what is going on. It might work better with a squirt of oil in the bore first, but I did not feel it necessary.

I used my old compression tester hose screwed into cyl no 2 and found that the long hose off my old Gunson CO tester was a nice screw in fit, giving me an air-tight pipe.

IMG_2124.jpgIMG_2126.jpg

Anyway, sods law etc, after all of that, it turned out that my TDC was bang on the zero marker at the crank pulley :-)

Cheers
Keith

[Westfaling]

Love the U tube method. I wouldn't have thought of that!
Nick

[jleyton]

Great post - well done Keith, very interesting.

I've got one of those endoscopes but can never make any sense of the images I see It is quite a cheap one though.

Cheers

Julian

[dasadrew]

The U-Tube method is great. The movement of the piston is multiplied effectively by the ratio of the piston surface area divided by the tube cross-section area thus giving a very good view of the exact TDC point! Great stuff!

Come on Chris (VMad) I'm sure you could add such a set-up to the keyway template method and produce a TDC measuring kit. Seriously.

Due to my cracked front pulley and that I have now two alternative replacements I checked TDC against all three and it was spot on in all cases.

Drew

[Bob Heritage]

Great post - well done Keith, very interesting.

I've got one of those endoscopes but can never make any sense of the images I see It is quite a cheap one though.

Cheers

Julian

That depends on what you're looking at

[Goldstar]

Love the manometer method, I just assumed that the pulley marks would be correct. Proves the old adage about assumption being the mother of.....

[72BLUE]

The endoscope method is easier and importantly more accurate, if you already have a laptop or tablet, I would not bother with making up a U-tube, if this is the case, just buy one of these or similar.......

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=300772387141&ssPageName=ADME:L:OC:GB:3160

(btw no contacts with seller etc and you might well find a cheaper one)

Cheers
Keith

[Rubce]

Hi Keith

Have you had it out on the road yet this year? I haven't see you out and about.

Regards

Bruce

[Mike Stevens]

I've also seen it done with a balloon on the plug adapter. However, the same issue with loss of pressure will occur and anyway, the manometer method would be much more accurate.

Brilliant stuff!

I've got one of the endocope thingies too. At £15 odd I couldn't resist it. I've not needed to use it yet, but I'm sure it'll come in useful one day!

Cheers,
Mike.

[dasadrew]

....I was surprised how quickly the vertical movement of the piston changed to from up to down btw, I had read that there was a noticable period of crank rotation when no movement occurs, from my experience here, there is hardly any 'slack' period.
Cheers
Keith

Due to the rotation of the crank pins, the vertical movement of the piston is a simple sine curve. At the top of the sine curve (TDC) one degree of movement of the crank translates to 0.0049 mm of vertical travel (0.2 thou). I'd certainly put that into the category of "hardly noticeable" !

If the measurement is out by 0.1mm, the difference is about 6°.

[72BLUE]

Hi Keith

Have you had it out on the road yet this year? I haven't see you out and about.

Regards

Bruce

Hi Bruce, yes I have been out, but not a lot! Now that my loom is rebuilt/upgraded, I am trying to sort out the engine. I bought it as having emission problems and the PO thought that the engine was burning oil. However, I think it is OK in that respect having done the usual tests, compression/plug colour etc. The mixture was way too rich at 11% CO, so I have been tuning the carbs and ignition. The points were way out (I have a Lumenition to fit......) the timing is next as following my TDC adventures yesterday I am sure it is at least 8 degrees or so out.

The big buggeration factor thought is that my son has bought the house opposite to ours due to a price that we could not refuse, so I am getting massively distracted by DIY. I have actually just come back from doing a bit of plastering. On the upside, the house comes with a brand new 30' x 19' garage and guess where my Stag is now.............................

On my next 'road test' I could always come for a blast round your way...........

Cheers
Keith

[72BLUE]

I've got one of the endocope thingies too. At £15 odd I couldn't resist it. I've not needed to use it yet, but I'm sure it'll come in useful one day! Cheers, Mike.

Hi Mike, give it a go and check your TDC gauge at the crank for accuracy. It really is a doddle and it would be good to get someone elses perspective on it as a useful technique.

Cheers
Keith

[72BLUE]

Due to the rotation of the crank pins, the vertical movement of the piston is a simple sine curve. At the top of the sine curve (TDC) one degree of movement of the crank translates to 0.0049 mm of vertical travel (0.2 thou). I'd certainly put that into the category of "hardly noticeable" !

If the measurement is out by 0.1mm, the difference is about 6°.

Drew, your knowlege never ceases to amaze me!

As I mentioned before, from reading previous threads here, I had thought that there would be a really noticable 'slack' period but this turned out not to be the case. This made it quite easy to work out TDC.

The endoscope gives a macro or close-up view of what is going on and (again, as mention previously) using the bottom of the image window as a datum line in reference to a given point/mark on the piston crown makes it easy to detect the smallest of movements.


Cheers
Keith

[KOY 23]

That depends on what you're looking at

Don't think I want to borrow it now.