Good afternoon Gents,
A few weeks ago I completed a top end rebuild on my M20, +40 piston new rings, valve guides, springs, rebuilt magneto & dynamo, its now a joy to start with just the weight of your gaze on the kick start enough to get her running. Because the weather is so mild today, I thought I'd have an hour this afternoon to get a few more miles on it. I noticed oil at the back of the cylinder obviously running from top to bottom.
On start up i observed fresh oil bubbling away below the head steady bolt at the new copper head gasket. I torqued the head down following Ian Wright's instructions to the letter, I've ridden about 25 miles in total and all at 25-30 mph. do you think I've cracked a ring because oil shouldn't be that high anyway should it?
Any help would be appreciated
Alwyn
email (option): Alwyndart@gmail.com
Did you use a solid copper head gasket or one of the modern crap composite things? Ron
email (option): ronpier@talk21.com
HI Ron,
And thanks for the quick reply.
A solid copper one from TT John,
email (option): Alwyndart@gmail.com
Well then something is not right Alwyn. Did you make sure all the bolts tighten down on the head before bottoming out? Usually with a solid gasket the bolts don't move much if at all on the second check. And if a ring is broken you will get white smoke from the exhaust. In any event if the gasket is sealing, any excess oil should go out the exhaust anyway. Ron
email (option): ronpier@talk21.com
HI Ron,
There is no smoke out of the exhaust, I'm not convincing myself that i checked it for depth properly, can i just remove that bolt and check it for depth clearance and then retorque (just that one), because there's oil there now, do you it may not seal again properly. or is it best to nip it off and start again! It's only an hour or so.
Thanks
Alwyn
email (option): Alwyndart@gmail.com
For the amount of effort and time involved, I'd pull the head off, check for any foreign body or anything else obvious, Screw all the bolts down into their respective holes and check that the part left is less than the thickness of the head. As belt and braces, I use "Welseal" according to their instructions. Some people fit them dry, some use grease and I use Welseal on the grounds that even if it doesn't do any good, it can't do any harm. Ron
email (option): ronpier@talk21.com
Is it oil or unburnt fuel combined with the carbon from combustion ? The gasket leak needs fixing, but pottering at running-in speeds can mean that carbon is not being burned on as it otherwise might. Flooding to start etc. will then wash the top of the piston and it can blow out, quite often at the exhaust joint.
Rightio
The heads off, both valves are bone dry, the piston head is covered in oil, is that looking like ring failure? I'm struggling to upload the photos.
Alwyn.
email (option): Alwyndart@gmail.com
The heads off, both valves are bone dry, the piston head is covered in oil, is that looking like ring failure? I'm struggling to upload the photos.
Alwyn.
Alwyn
email (option): Alwyndart@gmail.com
Well before you pull the barrel off, I'd say it's worth mopping the oil up and popping the head back for a few more miles to bed the rings in a bit....I presume the breather is working ok. Push a piece of rubber hose on the end of the pipe. You should be able to suck but not blow.
Ron
email (option): ronpier@talk21.com
HI Ron,
The breather isn't doing anything, I can blow and suck either way, not good, the reason for embarking on this top end rebuild was lack of power and unreasonable oil consumption.
On inspection you could drive a bus through the gap in all three rings, There was an oiley coked up residue on the piston top. Obviously becase of the increased compression its causing problems. So it's a strip down of the breather valve tomorrow, I assume it can be repaired?
Thanks again to everyone who's replied
Alwyn
email (option): Alwyndart@gmail.com
Starting to sound like a rebore and new piston :(
email (option): pes.sales@btconnect.com
It can often take quite a few miles to bed the rings in...If your breather was working, you might get a common symptom...For around 100-200 miles oil will 'spit' from the breather...If you were to place a clean sheet of paper under the bike with the engine ticking over, a few small spots of 'blown' oil from the breather would be apparent...Generally, this stops when the engine has run for a good 100 miles...I've noted this more than once...
If I were you I'd sort out the breather function and the head gasket to ensure it's correct and then do the 'paper test'... Then do some more miles before you start to worry over much......Ian
email (option): ian@wright52.plus.com
HI Ian,
The breather wasn't working at all but it is now, what is the disc inside the breather made from? When I blow there is some air getting past, I thought I'd make a new disc.
email (option): Alwyndart@gmail.com
rings installed with staggered gaps ?
email (option): richardpurkiss@hotmail.com
Saw you breify last week in Brecon military fair, I went over to say hello and you disappeared,
Yes they were staggered 👍
email (option): Alwyndart@gmail.com
Ok I've just made a new disc from a piece of commercial vehicle mudflap I purloined from a previous life, would the breather not working force oil past the rings and on to the piston top? One more thing how many miles do I need to do before I could consider in run in,
Thanks for everyone's responses
Alwyn
email (option): Alwyndart@gmail.com
Ron
email (option): ronpier@talk21.com
Yes, you are correct Ron it has had a rebore less than 25 miles ago, I'll double check the head bolt lengths again in the morning before I aneal the gasket and.......start again 😂
Alwyn
email (option): Alwyndart@gmail.com
As Ian suggested, you can often get some oiling till the rings bed in. Ron
email (option): ronpier@talk21.com
Did you anneal the head gasket before fitting it ?
As supplied most gaskets are some where between 1/2 to full hard because soft copper does not cut on a punch cleanly
If full soft you can leave a cresent indentation by rolling your thumb nail across it
The breather is a standard flap valve and needs to be hard, fairly sure it is bakealite
It does not move when you blow or suck through it because you can not do it fast enough or strong enough
Best test is to remove the pipe then hold some tissue near the outlet
You should see it blow quite hard but suck just a little
The flap valve material was 'Tufnol'...The same material that carb heat insulation washers and some electrical components are made from...I test the flap valve operation before fitting it to the crank case...It's easy to operate by 'blowing and sucking' when off the engine...Interestingly there are three versions of the fitting that holds the flap valve in place. BSA made changes both to the air capacity and material of the fitting at various times...OHV engines also use a larger diameter breather pipe than the side valves...Ian
email (option): ian@wright52.plus.com
Hello,
I didn't aneal the gasket because when I bought it from someone on this forum he stated it didn't need anealing as the copper was soft enough from new. I will aneal it when I refit it now for sure. As for the flap material I assumed it was made from a hard rubber and that mine had gone hard...DOH it's meant to be like that.
I've only anealed copper washers in the past and they turn dark when quenched, do you do anything to clean the gasket after anealing?
Thanks Alwyn
email (option): Alwyndart@gmail.com
Some people say you have to get the whole gasket cherry red, But I hang them on a hook and chase the red round with a gas torch. I never bother to quench, it works just the same if you quench or cool slowly. Once cool I clean them with wire wool on a flat surface.
Jan V. Who works with copper, told me that my method is quite acceptable and that's how he does it too. Ron
email (option): ronpier@talk21.com
Thanks for that Ron 👍
email (option): Alwyndart@gmail.com
Hello Chaps,
Just a quick update on the problem I reported just before Christmas, I anealed the copper gasket that had failed and refited it with welseal and it still leaked. I took it back off again but this time there was substantially less oil on the top of the piston than the first time, (suggesting Mr Wright knows what he's talking about)😂😂
I had a spare new copper gasket and this time I anealed it before fitting even though it felt soft at the start, afterwards it was very pliable indeed, Again I used a very thin coating of welseal on all surfaces as recommended by Ron, I torqued everything a couple of times and it looks like the Jobs a good-un. What did we recommend on running in miles 400-500?
A big thank you to all for your help and Happy New year to Everyone.
Best Regards Alwyn.
email (option): Alwyndart@gmail.com