Camshaft timing

[TedAllen]

I've just started timing up an engine. I have Mike Allfrey's comprehensive guide to this process which was posted on t' interweb.

I've always timed up by using the marks Jowett provided on the two sprockets but in his piece, Mike says to ignore Jowett's marking...fine. He mentions that the crankshaft sprocket can go on either way but I have no information on which way. Although I have always put it on with the 'dimpled' tooth facing outwards. There is a difference of about half a tooth depending which way it's fitted.

Can someone please let me know ?

Ted

[Forumadmin]

Do not rely on marks. Find TDC by checking when piston is at top in No 1 cylinder. This can be done with some soft wire through plug hole. Then follow Mike's method is my advice.

The timing disk can be printed using Philip Dingle's extensive article on his rebuild

Degree_Wheel_Template.png

Jowett_Engine_Rebuild.pdf

Engine_Rebuild_Log_Template.xls

Engine_Rebuild_Log_Template.pdf

[TedAllen]

Thanks very much for the reply. I have a disc, just need to fashion a pointer. I'll assume the bottom sprocket goes on with Jowett's mark away from the crankcase...... but I won't use the marks. I'm going to do a practice run on a spare engine I have on the bench before I tackle the one in the car.

I'd be interested to know why the Jowett marks are not reliable....I've always used them in the past 40 odd years but have to say I've never really had a smooth engine !

Ted

[Forumadmin]

I have no statistics on the marking reliability, but I have had some occasions when the mark on the flywheel was incorrect. Parts may be remanufactured or have been altered during their 70 year life. Anyway going back to first principles may take a little longer but instils confidence in the build when everything does line up.
Camshafts too may have been modified or be worn so checking the actual timing of the ramp on each lobe may show a lot of variation. See Philip's article on Valve Train. Wear on the camshaft bearing surfaces also greatly affects the lift due to the oscillating stresses on the camshaft.
Incorrect valve timing is like you trying to breathe when someone presses on your chest just as you are trying to breathe in or like trying to breathe through a small tube.

[TedAllen]

Thanks for the help Doctor Admin. Did a dry run on the engine I had on the bench first. Then tackled the one in the car. No problems as the flywheel markings were correct in both cases for TDC. Only difficulty was using the gauge on the inlet rocker on the fitted motor...mainly hard to mount it where you could actually see the reading but after lying on my back and getting up to turn the crank a little each time it was ok. But I was knackered ! That bonnet catch bar is ideal for the elderly to pull themselves up on...thanks Jowett !

I fitted the timing cover with three bolts so I could fit the dizzy, blocked the oil filler and fuel pump aperture with tissue, cleaned the plugs and fired it up for a few seconds. It was a lot better, I even managed a quick rev up. Mixture too weak of course with the balance pipe open at the pintle end but it was ok on choke. Need to put it all back together now and tune the ignition and fuel when it's warmed up with it's cooling system and alternator back on.

I guess the top sprockets were not in the correct place on the camshafts...a fault perpetuated over the years by just fitting the shaft and sprocket as an assembly every time.

Ted