MkI Square Four - my problems continue

[Gui.dorey]

Hello chaps,

Picking up on my troubles from last year, I need some input again from the experts here. As you know, my MkI has two major problems:
1. The head gasket keeps blowing - always on Nr. 3 at 6 O'clock, and even though I have tried every thing, from Ottos to copper gaskets, following strict assembling, torquing and running in procedures, and lighting a candle to the motorcycling gods, nothing has helped. As a last resort I think I shall be trying a spare barrel which I was able to find during the winter.

2. My bike keeps blowing an incredible amount of oil out of the timing case breather. At the end of the season last year we speculated if the spring on the front crankshaft pressure relief valve could be too strong , thus causing too much pressure inside the timing case. An unlikely scenario, but I did replace the spring with a weaker one to try it out.

Yesterday I finally was able to go for the first ride this year. She started brilliantly on the first kick, and the first 20 km or so were pure bliss. Very smooth, pulling strong, just marvelous. Then the ominous chirping when under power telling me the gasket was about to go, and 15km later it was pumping hot air out of Nr.3. I arrived home after 42Km, having to pull out the choke a bit, as it was sucking air in through nr3's head, weakening the mixture and the Sq4 was very unhappy - but it got me home.

Because of the oil pumpimg out of the timing breather, I plumbed a hose to a small container to catch the oil, and indeed after the 42Km I found I had about two fingers of oil in the 250ml coke bottle I used as a container. That is an abnormal amount of oil, as you will agree. Obviously, the weaker spring on the crankshaft's pressure relief had no effect. And to recap, pressure cannot build up on the Sq4 as two cylinders go up as two go down, and all my rings are intact - I checked.

So we come back to the same question - what can be causing this? One thought that occured to me was if the Morgo pump is not pumping enough oil back into the tank?

Anyway, this morning I decided to open up the timing case and run the engine to see if I can spot anything. I put my finger over the hole into the crankcase (it's the hole between the crankcase and timing case about half way up the wall and towards the back) and I don't feel any pressure coming from there, not even a slight pumping, so that seems to rule out a pressure build up inside the cases. What one does see is an lot of oil coming through the rear crankshaft plain bearing. It seems that at that rate the timing case would very soon fill up with oil, eventually reaching the entrance of the breather and just flowing out. Looking at the return into the oil tank, there was a very steady flow, so it seems the morgo is scavenging like it should. If it's enough, I don't know. My question is if the amount of oil flowing into the timing case through the plain bearing seems normal to you, or if it is too much and is an indication that something is wrong somewhere?

I've attached a picture. I do have a video, but I am not quite sure how to attach it here. On the picture one can see a stream of oil just below the rear crankshaft - this is a steady flow while the engine is idling) I'll be very interested to hear your opinions.

Cheers
Gui

[Gui.dorey]

trying to post the video. Let me know if it works.

[simon.holyfield]

That works Gui

[roger.fellows]

Hello Gui, I've never tried running without the cover on, but that looks like a heavy flow. Others will comment I expect.

I can't remember exactly where your timing case breather is positioned. Maybe you need to make sure that anything dripping/thrown off the chain falls clear of the breather?

It's probably difficult to assess any crankcase pressure as the camshaft bearing acts as a breather too, and there are drain holes by the lower edge of the main bearing.

I suspect that the morgo will be pumping much more out than in. One problem which can occur, though, is that the end of the pipe from the sump bears on the lower part of the mesh strainer. This can mean that bits of debris are picked up from below the strainer and block or restrict flow from the sump.

I've not seen the pattern of the stop you have under your tensioner before. It is much longer than what I am familiar with for a simplex chain, but looks shorter than the type which is used with a duplex chain. If you're using a duplex chain, I believe it should run directly on the stop. I'll try to find some for comparison. If it's the duplex type, somebody probably wants it!!

[Gui.dorey]

Hi Roger,
I‘m running a simplex chain and the tensioner is the correct one for a MkI. Sort of. My tensioner was missing and I couldn‘t find a replacement so I fabricated one myself based on pictures. But it works fine.

Regarding the breather: you‘ll see a copper pipe running along the top of the Morgo and disappearing just under the tensioner - that‘s where the breather hole is. You might even make out a small wire holding it to the top bolt of the Morgo. On the Mk1 the breather is just a hole on the back wall of the timing case where that pipe is attached to. The pipe is a mod, basically bringing the entrance to the breather to about where the cam wheel is, on the upper right corner of the timing case. This is to reduce the amount of oil going out the breather. The theory is most of the oil gets picked up by the timing chain and accumulates around the dynamo sprocket and runs down the back wall straight past that breather hole. The least amount of oil is around the cam sprocket where the inlet for the breather now is.

[roger.fellows]

Hi again, Gui, how much blow-by do you think there might be, either into the rocker box or past the pistons - that is where any crankcase pressure will come from I presume.

The breather hole is common to Mk1 and Mk11. There are various mods fitted by people now.

Bruce Longman's instructions for fitting a cam spray bar include the suggestion of an extra hole between crankcase and timing chest. Have you seen that possibility?

[Gui.dorey]

Hi Roger,

I actually don‘t believe I have any blow by. At least I haven‘t seen any evidence of it.

The only thing I know is that I have large amounts of oil coming out of the timing breather. Why? That is the question.

I haven‘t considered further mods like an extra hole, because I believe that if everything is assembled and working properly, there shouldn‘t be any need for further mods. There are many Sq4 running perfectly fine without extra holes and without spewing half a litre of oil/100Kms out the breather. In other words I need to find the cause first before starting experimenting with modifications. Something is clearly wrong, but I‘m missing it...

[simon.holyfield]

Gui, did you record the finished dimensions of the rear offside main bearing? I've never run the engine with the timing cover off, but I have run it with the front offside main bearing cap off and mine doesn't lose oil out of the bearing like that.

[roger.fellows]

Please forgive me for a stupid question, Gui.

You do have the 'oil seal washer' fitted behind the crankshaft sprocket, don't you?

[Gui.dorey]

Simes, I didn‘t... but I seem to remember both front and rear were a good sliding fit, but it‘s 2 years back now. On mine, the front one also doesn‘t let out so much oil out. Could be a normal difference though, as the rear one gets the oil first which then has to find its way to the front one, and there‘s the pressure valve as well. Don‘t know if all those factors would make a difference?