Tuesday, February 16, 2016

Valve Timing Turmoil - To Belt, or not to Belt

In the previous post, I made this fantastic (...ly free) timing protractor, so now I suppose I'd better put it to good use and get my money's worth out of it. It's time to check the valve timing...

Front Plate
Before anything to do with the valve timing can be considered though, I need to get the front plate mounted up into place with some RTV and a new gasket. Just like all the other times, all the surfaces are de-greased with brake cleaner and the gasket prepped with a light smear of RTV.

Once it was bolted into place, the timing gears were loosely mounted along with the chain and tensioner.

Now, as they were mounted in exactly same position as they were last time I built this engine, I assumed the timing would still be the same 110° after TDC, which is the required spec for the camshaft. Seems a safe assumption, but I thought it best to check anyway, so whipping out my fantastic protractor and dial indicator, I got to work measuring the timing.

This post here, goes over the whole valve timing process in some detail so I won't repeat it here, needless to say though, I didn't get the reading I was expecting. After checking it several times over, I was left scratching my head as the timing had now dropped back to 108° after TDC!!

After doing a little research on the subject, it seems that the most likely reason for the discrepancy is down to chain stretch. Yes, I know that given the humble spec of my little engine, the timing being out by 2° will make virtually no difference at all, and to be honest, I'd have probably lived with it had I not read that a new simplex chain can stretch to be upto 15° out!!!

The Turmoil
This is where the turmoil comes in as I can't live with a 15° timing error, especially as I'm going to all this effort to make the engine the best it can be!! So what to do? I thought of a number of different ideas; I considered digging out one of my old chains in the hope that it was already stretched as much as it was ever going to and presumably would stretch no more, but didn't like the idea of that. Then I thought about getting a new offset woodruff key to correct the discrepancy, but what offset would I get, a 2°, a 5° ? I had no idea as I don't know how far it will stretch in the future.

I also considered splashing out on a new adjustable duplex chain, but they are currently just over £100 and I don't really want to spend that kind of money at the moment. Also I'm pretty sure I would need to get a new timing cover which would bump the cost up further.

My last option was to look again at the belt drive I bought last year. I managed to pick it up quite cheaply as it was in a bit of a state and a few bits were missing.

Although I had spent quite a lot of time fixing it up, replacing the oil seals and sourcing the missing nuts and bolts, I decided not to use it during the initial engine build as I couldn't get hold of a new belt as they were like hen's teeth at the time.

The other issue is that some believe that a belt is just not as reliable as a chain. The number of times I've heard people say 'You never hear of a chain snapping' and the problem is, this is a very compelling argument, I don't want to risk knackering up my engine if the belt snaps do I?

The main problem with a snapped timing belt is the valves hitting the pistons and getting all bent and battered. In fact this very problem has happened to me in the past with an old Vauxhall Astra I once owned and as I remember it was a total disaster!

However after doing a bit of tinkering, I've come realise that the valves in this engine never come down far enough hit the pistons, ie; I don't have an interference engine. So what's the worst that can happen if the belt snaps;  well the camshaft would stop turning, which means that the oil pump would stop pumping resulting in a sudden drop in oil pressure, which is bad. However, almost simultaneously, the engine would stall anyway!! I'm talking myself into using the belt aren't I!!

Also the belts are now available again from Mini Spares, albeit at the rather extravagant price of £41.40. Also did I mention that the belt kit is adjustable and never stretches!! You can guess where I'm going with this, I'm getting a new belt and giving the kit a go!!

Which is exactly what I did! It may seem a bit mad putting a timing belt conversion on such a small spec engine, but I'm afraid the Have a go Hooligan got the better of me on this one and just took over.

Belt Drive Conversion
Even though I managed to track down the instructions on the internet, there's quite a bit of fetteling needed in order to make the housing fit properly.

The camshaft housing plate bolts need a little trim, so they had to be taken out again, filed down and re-torqued back into position.

The next issue I came up against was that the replacement bolts that I had managed to source were too long and were bottoming out against the side of engine block, which was a bit of a pain.

Not to worry though as they were soon cut down to size with a junior hacksaw to fit perfectly.

Once the housing was on it was starting to look good...

The next and I hope last problem to conquer is that the standard crank pulley does not fit with the new housing because of the extra bit of metal it has riveted to it's backside!!

What is that for? Although I searched and searched and couldn't find a definitive answer, but I did come across a forum where they had drilled out the rivets and removed it and there was no ill effects. Luckily I had a spare pulley, so it got drilled out!!

And it fits!! Not just that, it even lines up with the pulley above!!

Timing it in
As a means of increasing accuracy, I found it helpful to use my old smartphone in a tripod with the light on, zoomed in on the protractor pointer. This has two main advantages in that it magnifies the protractor so you're good to about a quarter of a degree, but it also ensures that you always take a reading from the exact same perspective each and every time removing the possibility of any parallax errors.

After a few attempts at getting the peg in the correct hole, the timing was back to the magic 110° after TDC.

Now the cam nut needs torquing upto 61 - 64 bl ft, the problem is though there's nothing to lock the camshaft while you do it. I can of course lock the crank by jamming the flywheel and rely on the strength of the belt to pull against, but I don't want to risk stretching the belt.

After a little head scratching I came up the a rather crude but effective way; jam the flywheel to lock the crank, which locks the smaller timing gear and then wedge in a bit of wood between the two timing gears to lock the top one.

Lock the crank

Lovely bit of wedgewood

and done!!

Last job is to put the cover on and it's all done.

Well almost, I will be giving the pulley a lick of paint before it's finally bolted into place.

I feel like I should apologise for the length of this blog post, but it kind of reflects the long drawn out process I went through to get here. I really went from one solution to the other and got tied myself up with different ideas over the last week on this problem.

Did I go with the right idea in the end? I'm still not sure really as there is an element of a risk fitting the belt as it's very much an unknown quantity. It could be good, it could be bad, but I really wanted to give it a go so I just hope it turns out well.

As always, I'll I'll keep you posted.

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