Tappet adjustment - TDC on Greaves/Lombardini?

[fishlegs]

My greaves enfield's running great. I haven't had any trouble kickstarting using the recipe: (Turn the motor over until compression, pull decomp lever and turn over until I hear "the injector gronk," pushing it a little further so the decomp lever clinks back). But now as I undertake my first tappet check and adjustment just to be on the safe side, I'm a bit unsteady on exact piston placement. It seems the tappet clearance changes pretty abruptly as I gingerly turn the engine over, making me want to be dead certain that I'm adjusting at the proper point. I've removed the shroud cover in hopes of finding timing marks on the flywheel, but so far I haven't found any.

I imagine that if my decompressor adjuster was improperly adjusted, it could impact my perception of where TDC is, since I usually wait for the lever to 'clink' off.
Should I stop turning the engine over after the "gronk," even if the decomp lever hasn't clinked back yet? And at that point, should I push the decomp lever back to its resting position so it doesn't affect my exhaust tappet clearance?

Is there a way to know when to stop turning the engine over based on when the exhaust rocker arm begins to descend? Or any other cues?

Sorry for the plodding inquiry. And many thanks for this great forum.
-erik

[Diesel Dave]

Hi Eric,

If you turn it over 'till the injector 'gronks' then your close enough to do a tappet adjustment.

The other way to do it is to adjust the inlet when the exhaust is fully open and the exhaust when the inlet is fully open.

There is a long dwell period with the tappet 'off cam' and any point can be used for adjustment.

If your decomp is flicking off OK then it's prob adjusted correctly, the valve clearances are 2 thou which is as small as a Honda.


Have you tried the bounce start technique - it's easier.

http://www.youtube.com/watch?v=j_U-JltnGig

Cheers
Dave

[fishlegs]

Thanks Dave.

I went ahead and checked and adjusted them at the point just after the 'gronk,' but I still feel a bit washy on the precision end of things. I got different clearances every time I turned the engine over and tried putting the piston in that same position, which seems like it would matter if we're after 0.10 - 0.15 mm of clearance.

The bike still kickstarts and runs fine. There is a metallic rattling sound intermixed with the thumping of the engine, that I'm not sure was there before, making me wonder if the tappets are now too loose.

[Diesel Dave]

You need what's called a tight sliding fit.

The feeler gauge should fit tightly betwixt rocker and valve but still slide out with a light pull.

Dave

[fishlegs]

I'm comfortable with using feeler gauges and regularly perform valve adjustments on diesel mercedes; the concern I have isn't how to use the feeler gauges so much as when to use them. I just need to figure out a more precise way of knowing that the piston is exactly where it needs to be for me to check the tappets. Perhaps I should pursue the other method you mentioned "to adjust the inlet when the exhaust is fully open and the exhaust when the inlet is fully open."

thanks,
-e

[Diesel Dave]

There's nowt for it then, pop the head off and scratch the flywheel with a TDC mark.

Dave

[Sphere]

I can't fathom that a lombardini would not have a TDC mark. How is one to adjust things then?

[Crazymanneil]

Don't know if it helps but I've used a screwdriver dropped through injector hole to determine TDC. Seemed to allow reasonable accuracy (in my case I needed to work out cam timing so close enough to be right within one cam sprocket tooth).

N

[fishlegs]

Thanks Neil. The screwdriver in the injector hole trick worked great. I feel considerably more at ease with my newly made TDC marks. The tappets were in fact a bit loose.

[Crazymanneil]

Cool I helped someone

I guess you could get real obsessive with a dial gauge etc but never felt the need myself.

Used this trick one time when setting valve timing on a mates SV650 and we were not 100 percent sure what the manual was talking about. Unfortunately we were still a bit too enthusiatic and forged ahead despite concerns, bending 2 valves in the process. Lesson learned I guess...

N

[Sphere]

I'm sure that last story is really reassuring for fishlegs

[Crazymanneil]

Hmm, yes. In fairness though we really should have noticed cam lobes pointing down while screwdriver was at top of travel. Worked the best on the Smart engine though (timing mark on pulley which I didn't have at the time).

N

[fishlegs]

Well at any rate, I need to pull the head off tomorrow to fix the gasket. So we'll see how close the screwdriver method got me to TDC.

[coachgeo]

I have heard something about a string/rope method for finding TDC. Maybe try google search for something along this line. Rope won't damage valves or piston tops like a screw driver can

[Diesel Dave]

To do TDC properly with the head off you need a dial gauge, the vertical movement is tiny compared to the rotational.

The other way I've used on petrol motors is to use a piston stop say 10mm before TDC, mark this one way then rotate backwards and mark the opposite - TDC will be dead centre between the 2 marks.

Dave

[sbrumby]

If you are only trying to adjust the tappets I think you are makeing it far too complecated. When the valve you are trying to adjust is down rotate the flywheel 360 and adjust.

[Diesel Dave]

Your sooooo right there Sam.

BTW can you get me a pair of those Honda rubber isolated mirrors that your bikes have, from your mates barn of useful bike bits?

Cheers
Dave

[sbrumby]

none left in barn, available at http://www.getgeared.co.uk/LOUIS_Motorc ... tegory=276.

[Crazymanneil]

I'm enjoying this thread now. Fishlegs, have you got a dial gauge? It would be interesting to see how far off your mark was just for curiousity sake.

N

[mark_in_manchester]

>I have heard something about a string/rope method for finding TDC. Maybe try google search for something along >this line. Rope won't damage valves or piston tops like a screw driver can

This brings back fond memories...a piece of rope can be used to lock up an engine, when you need to do something to it which would normally require taking off the barrel and piston, and putting a bar through the small end. Instead, you take out a plug, feed a load of rope through, and then roll it over gently until the rope squashes against the head. I used this to get the clutch off an MZ250 by the side of the road when stranded in North Wales once, having emptied the oil into my top box...a futile exercise as the clutch taper (on which clutch sits on this bike - no keyway - daft design when it fails and picks up) on crank was buggered. Happy days...

[Sphere]

I suppose this is the point at which you are going to tell us some sheep got you on your way again?

...stranded in North Wales once...

[fishlegs]

A report on the screwdriver trick:

I had the head off the other day, to try to improve my head gasket seal, and I took advantage of the opportunity to check up on my homemade TDC mark. Unfortunately I don't have a dial gauge, so I made due by "mounting" a dial caliper over the piston to take depth measurements as I turned the engine over. The screwdriver method did get me very close to TDC. My "screwdriver method" mark on the flywheel is about 3mm off rotationally from the dial caliper mark.

As a note to prevent valve bending, I wasn't leaving the screwdriver in the injector hole while turning the engine over. I'd rotate the engine a bit, insert screwdriver (or plastic rod) into the injector hole, note height, pull out the rod, turn engine slightly, put rod back in, etc.

[Crazymanneil]

Good stuff thanks for posting back.

Just to clarify the sv650 incident with bending valves was due to cam timing being incorrect. This was despite screwdriver trick telling us piston was going up while cam lobe was pointing down.

N