Engine assembly questions.

[Ruairidh Dunford]

You can measure the backlash at meshing point using a narrow feeler gauge (a bit more easily done if no load from valve gear) - ideally I try to get as near to 4thou as is possible, much more than this and I find the do chatter.

[Ian Williams]

You need to be careful not to reduce the end float below 2 thou, I slightly over lapped one once and then found the engine would lock up completely when it got hot, only to free off again as soon as it cooled down slightly! Took a bit of head scratching until the penny dropped

[Peter Lawson]

Hi Steve, thanks for that tip. Will remember that! Very useful.

Endfloat is correct I think. I did the lapping trick until I got it to the correct figure when tight. I'll see if I can measure it in the engine now with the dial gauge to check though.

Looks like I'll be home today with a cold so I will see if I can film what's happening and show the amount of backlash later on when it's light.

There is definitely a lot of backlash but what worried me more is it seems inconsistent all the way around. More in some places than others.

A pain to have to take all that apart again but much easier to get it right now with the engine half assembled on the bench than in the car!

Simon

Hi Simon,

With reference to your use of a silicone base gasket, I'm helping Stephen Barker rebuild his engine with such a gasket from the Seven Workshop after successfully fitting one to my Ruby (no more leaks). Bear in mind that when the block is tightened down on to this it squashes about 1mm so you can't get an accurate valve clearance until this is done because you are effectively altering the distance between your cam followers and camshaft lobes.
After assembling the block and pistons I too noticed a slight noise from the timing gears when turning the engine over by hand using the flywheel. It seemed to occur only when the pistons were reaching TDC. I then held my hand on the camshaft gear to create some drag and the noise lessened considerably so I assumed this was a bit of backlash. However when copious amounts of oil were squirted over the gears it all but disappeared.

Good luck, Peter.

[jansens]

I managed to make a little film (and managed to crush my finger between flywheel and crankcase!) but you can see the clicking here.



I had previously checked the backlash with thin strips of shim metal and I seem to remember it was about 5 thou. The block isn't really tightened down yet so I just set the tappet clearances to 6 thou and did them up finger tight. I will reset everything once it it all done up properly of course.

I am sure A7 engines are assembled that make more noise than this but I want to make sure nothing it wrong or broken or likely to cause issues later on. I did try spinning it with a drill slowly from the flywheel to make sure it wasn't how I was turning it and it makes quite a racket!

Simon

[Bob Culver]

Used timing gears do not wear uniformly.
The front of the crank in particular deflects here and there when running. One local had a timing gear break from its hub due insufficent clearance.
Some other makes had an extra cam and spring loaded follower to counter the reverse effect.
Many others used fibre gears and from Model As to Holdens all failed eventually.

[jansens]

I know it's better to run more clearance than tight but that this makes them noisy. I just don't know what noisy means in this context.

[Ian Williams]

Simon provided lash is not significant do not worry about a little bit of noise as the cam flicks over on the valve springs, this is perfectly normal. It is important however that you check the cam timing, particularly as the face of your gears do not appear to be in line with each other, that in itself is unimportant but the timing is, Paul should have given you figures, adhere to them. The peg hole in the crank case and cam bush are often damaged and are also not a great design as standard, we have talked in the past about improving this, in doing so you should make sure the bush is located fore and aft correctly as this affects your cam timing. I usually plug and re drill both the oil way and location hole so I can dial things in and ensure correct opening/closing, if really enthusiastic and wanting to experiment further you can make a vernier cam wheel from two old gears.

[jansens]

Simon provided lash is not significant do not worry about a little bit of noise as the cam flicks over on the valve springs, this is perfectly normal. It is important however that you check the cam timing, particularly as the face of your gears do not appear to be in line with each other, that in itself is unimportant but the timing is, Paul should have given you figures, adhere to them. The peg hole in the crank case and cam bush are often damaged and are also not a great design as standard, we have talked in the past about improving this, in doing so you should make sure the bush is located fore and aft correctly as this affects your cam timing. I usually plug and re drill both the oil way and location hole so I can dial things in and ensure correct opening/closing, if really enthusiastic and wanting to experiment further you can make a vernier cam wheel from two old gears.

Thanks Ian, cam bush has been sorted out as you have suggested. I have a stud in there and when done up it's all nice and tight. I do need to adjust the cam timing as you say. I aligned them as per the dots on the gears but that doesn't match what Paul told me to set it to so I need to change that. It looks about a tooth off I think. The gears are actually in line, I made sure of that when I was setting up the end float (and I just checked with straight edge across the faces again to make sure). 

It did occur to me the noise I hear sounds far worse in a quiet garage with no other noise about. In a running engine would it even be noticeable?

Don't try and get me onto more complicated things with vernier cams! Am having enough trouble getting the basics sorted at the moment

Even the basics are tricky. Steve gave me a good nose cone to use that will be correct for my engine and radiator (I was going to cut down a Ruby one) but I just discovered the diameter of the starting handle bosses is different so the one I have won't fit. There are a ton of little details on cars like this with such long production runs and changes that can trip us new players up.

Simon

[Ruairidh Dunford]

I don’t wish to simply repeat what others have said but, for completeness of your answer to my question, if you have 5thou back lash I think you will be fine. The click is normal for the reasons described above.

The silicone gaskets I use do settle after a couple of tightenings, only after this do I set the tappers and it is at this point you should repeat your head clearance test, without the gasket - to be sure nothing is touching.

[Ian Williams]

Aligning the timing marks may suffice in a std car, but is not really good enough if you want to extract maximum performance. The way Austin gears are cut means that moving them fore and aft in relation to each other will alter the cam timing, I have in the past had to broach new keyways in the crank gear to obtain the timing I was after.