Timing Valves without Timing Marks

[Jamie]

I have fitted the crankshaft and the camshaft to my engine and should like to set the timing of the two before I fit the pistons and the block, if possible. However, there are no timing marks on the camshaft pulley, although there is a dot on the crankshaft pulley.

Is there a way to set the valve timing without having the pistons, block and valves in place?

Regards,

Jamie.

[Bob Culver]

If the timing gears are a pair, and the cam standard the nearest tooth will be correct and does not need great precison. The valves ""rock"" ie are both equally slightly open 7 1/2 deg ATDC. For that the upper flanks of both cams should be equally just above horizontal. Easily established by eye ,assisted by laying some thin sheet across them.

To check in detail have to establish tdc, a bit tricky without piston to obstruct. A vernier calliper depth rod useful. Or a narrow flat surfce horizontal object projecting into the crankacse cyl opening and obstructing the crank rotation enable tdc to be determined from the half of the angle obstructed.

If cannot judge cams as above,a bare block with just two equally adjusted cam followers and two valves without springs all that is necesary.
May be differnt for a reground cam.

[Stuart Giles]

Setting cam timing accurately without a piston to set a protractor to TDC is going to be near impossible IMO. If you temporarily drop the block on and fit No. 1 piston and rod -no need for any pistons rings- and a tappet in number one inlet, then it's a simple job. Factory cam timing has maximum inlet lift @ 110 degrees after TDC.



There are loads of Youtube etc. videos on how to set a protractor accurately for TDC and how to measure each side of maximum lift to get the timing spot on. It's OK to run the cam a few degrees retarded in a light special as you will get more top end power. Run it advanced and the car will feel dead. I always "dial in" cams, not least because after 80+ years, you can't be sure that the gears you are using are a factory matched pair even if they do have the marks on them.

[Jamie]

Thank you, both, for the replies. I thought that it would be necessary to wait until the pistons are in to do the timing properly, but had hoped otherwise. I shall be patient and await the pistons' arrival. Thank you for the details guidance as well as that will help when I do it.

Regards,

Jamie.

[Jamie]

I now have the bottom end of the engine assembled, the conrods and pistons fitted, the cam in the block and the block attached to the crankcase. Before I try setting the timing of cam, can I check my understanding is correct? 

Step 1. Attach a degree wheel to the crankshaft.
Step 2. Use degree wheel and a dti to find top dead centre on piston one (nearest the front of the engine.). 
Step 3. Use degree wheel to advance the crankshaft to 110°.
Step 4. Use a DTI and and rotate camshaft until the second valve from the front is at maximum lift.
Step 5. Ensure crankshaft and camshaft do not move and fit it the camshaft and crank gears.

Have I understood this correctly?

Regards,

Jamie.

[Stuart Giles]

Hi Jamie,
            To be confident of accuracy:

Step 1. Attach degree wheel to crankshaft
Step 2. Fit a piece of welding rod, wire coat hanger etc. and set it to roughly  TDC on the disc.
Step 3. Fit a plate like the one in the photo below with a bolt in it that prevents the piston coming all the way up to TDC.

Step 4. turn the motor clockwise till the piston touches the bolt and stops. -note down the before/after TDC reading on your disc.
Step 5. turn the motor anti clockwise till the piston touches -note the before/after reading on your disc.
Step 6. You will have a difference between the readings off the disc -e.g. 20 degrees, if so, the true TDC is half the difference, 10 degrees forward or back of the two places where the piston stops. Just using a dial gauge on the piston isn't likely to give a true TDC as there is dwell either side of TDC.
Step 7. put your dial gauge on number 1 inlet valve, turn the motor over and note the highest lift reading on the dial gauge.
Step 8. Turn the motor over again, until 2 thou short of the highest reading; note the ATDC degrees off the disc.
Step 9. turn the motor a bit more until the guage goes past the maximum lift figure and reads 2 thou short; note the ATDC degrees off the disc.
Step 10. add the two ATDC degree figures together, then divide by 2 - the resulting figure is the true maximum lift reading. In the same way as there is dwell of the piston around TDC, there will be dwell around the maximum lift of the valves too.

This method might seem a bit of a rigmarole, but it does provide utterly repeatable results.

Edit: Once you have set the disc and pointer to the true TDC at step 6, remove the plate which stops the piston going to TDC; otherwise the next steps will be impossible.

[Jamie]

Thanbk you, Stuart.

I shall have a go and let you know how I get on.

Regards,

Jamie.

[Jamie]

I think that I am being obtuse. I have had a go at doing this. Setting the degree wheel to true TDC on piston one is fine. After that, I get confused. Without the timing marks on the gears, how do I know where to mesh them? I keep getting different values of after TDC for maximum lift, depending how the cam is rotated before I mesh the gears. I am sure that I have misunderstood something, but I am not sure what.

Regards,

Jamie

[Stuart Giles]

I think that I am being obtuse. I have had a go at doing this. Setting the degree wheel to true TDC on piston one is fine. After that, I get confused. Without the timing marks on the gears, how do I know where to mesh them? I keep getting different values of after TDC for maximum lift, depending how the cam is rotated before I mesh the gears. I am sure that I have misunderstood something, but I am not sure what.

Regards,

Jamie

Hi Jamie, If you have a look at the A7 timing chart in my first post, you will see that the inlet opens @TDC and the exhaust closes 15 degrees after, this is the normal 'overlap' when the motoir transitions from the exhaust to inlet cycles. Get the cam so that these two valves in number one cylinder are "on the rock" and then by eye, set the piston at TDC, now you need to fit the crank gear so that you still have that situation; because the gears are helical, this may take a few attempts. Once you've done this, mark the gears with two dots with the motor at TDC using something non permanent like tippex or a paint pen.

Then you are ready to do the steps I outlined earlier. If you follow the steps you should get consistent results even though the cam timing will almost certainly be wrong at the first attempt. However, with your Tippex markings you now have a reference point to advance or retard the cam against in order to get your timing to match the Austin figures in my previous post. Once you're confident you've achieved that, you can permanently mark the gears.

[Howard Wright]

Hi Both

Just a comment to say how much I’ve got from this thread.  I’ve always been able to put the gears together using visible marks.  However in my next engine build I intend to check this using Stuart’s instructions.  This may lead to an offset key so I’ll be back asking question about that in the future!

Thanks both

Howard