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Is this normal? with Photos.

I waited long enough to get my head sealed. Yesterday I pulled the head. I blued the head surface (You might call it something else in the UK, its a blue dye you use for lots of things in a machine shop. Sometimes its red) and put it on a surface plate with some fine sand paper. Not a low spot or high spot to be found. It removed all the blue evenly. I then re-annealed the gasket to be sure (I didn't install it originally so I need to rule that out). I will get back to this later.

First off. Someone with more experience with M20's can look at these photos and respond. The reason I pulled the head was because once hot, the bike seemed to bubble oily goo. It also would start to run a bit lean and idle up when hot.

Before I install the head I want to be sure everything looks normal. The valves look good to me. The seats look nice and shiny. My concern is that there seems to be alot of oil sitting on top of the piston. It has never smoked. It doesn't wet sump. So obviously the rings are the culprit. But is a little oil on the piston normal? Also, I have never ridden the bike longer than about 20 minutes.













I also have one head bolt that wont torque. In your experience would you run a die over this and tap the threads? Or should I skip that and helicoil?




Hope all the photos dont bother anyone. Im a very thorough person

Many Thanks,
Michael

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos.

My 2 cents, way too much oil in there. But then, I don't ride my bikes for hours on end. Would hate to fool with the threads. Screwed up one crankpin yesterday. Never found helicoils to be strong enough for heavy torquing.

Shade tree mechanic here.

email (option): unpob@yahoo.com

Re: Is this normal? with Photos.

I think a certain amount of carbon up top is okay - is necessary even to insulate the combustion chamber. But that looks a little TOO oily to me. The honing looks a bit iffy too. But keep in mind that if ever you see an M20 expert, I'll probably be a standing a long way from him. Looks like compression test time.

email (option): dannydefazio@sumpmagazine.com

Re: Is this normal? with Photos.

I wont comment on the hone. Sometimes people will do a light hone with a item we in the states call a "berrybush". A bunch of round stones on the ends of wires. I personally dont find the hone to be that bad. Its very crisp and smooth to my fingers. Even when a new liner is installed you usually hone it lightly to give the oil a place to stick to the walls. I could very well be off here. Im open to all opinions.

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos.

I had more or less that same problem after fitting a new piston. After replacing the (new) old piston rings the problem was solved. For some reason the rings that came with the piston didn't run in properly and gave the same problem.

Carbon build up on the inside of the cylinder bore can be tough and even stronger then the aluminium of the piston. Once it has grown bigger and bigger it can start damaging the piston.

Henk.

email (option): ahum@quicknet.nl

Re: Is this normal? with Photos.

Hi Michael..I would say you have far too much oil present on top of the piston. Often bores are honed to provide a better surface on a cylinder that really needs a rebore. Don't forget that honing may have increased the piston to bore clearance beyond serviceable limits if both bore and piston were already worn.
I would have the cylinder off the bike and measure both the bore..at various points along its length..and the piston to determine exactly where you are.
It may also be the case that the rings have been incorrectly gapped in the past or the bore is worn such that the ring gap is too large.
Valves should also be checked..particularly the exhaust.. to make sure the valve face is 100% true to the stem (it is surprising how often refacing the valve on a refacing grinder shows up this problem), as well as looking at the condition of the seats in the barrel.
The head bolt looks quite badly deformed...probably due to carbon or dirt that has been forced into the thread in the past...I would helicoil the barrel and fit a new bolt. Torque up to 28-30 ft. lbs when refitting the head and follow the tightening sequence in the manual...Ian

email (option): julie@wright52.plus.com

Re: Is this normal? with Photos.

Thats what I was expecting. Just didn't want to admit it.

I will take it down and check everything out.

Report to follow.

Many thanks!

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos.

Its been scientificly proven, at least the articles i have read, that the heli coil fix makes stripped holes stronger then when it was new!!!!

email (option): rcassin@aol.com

Re: Is this normal? with Photos.

Thanks Robin, the ones I referred to, were used in Aluminium and perhaps for that reason, they did not hold. Cast iron sounds better as I see Ian does not shy away from it.

email (option): unpob@yahoo.com

Re: Is this normal? with Photos.

When I took my head off, one bolt was already helicoiled and given good service for some time and one sheared off and I had to helicoil it, I will know how good a job I did when I finish the rebuild.

email (option): stinkypete80@hotmail.com

Re: Is this normal? with Photos. UPDATE

I pulled the cylinder and took some measurements.

Bore (measured at top of cylinder)= 82.3mm

Bore (measured at bottom edge)= 82.4 mm

Piston (measured at top edge above rings)= 82 mm

Piston (skirt)= 82.1mm and 82.2mm kept getting these two measurements.
Uppermost ring end gap = 10 thou.

Middle ring = 12 thou.

Broke bottom ring trying to remove it

On the bottom 1/3 of the cylinder I can see all of the nice crosshatch/basket weave hone. On the top half its visible but more worn.

Whats the trick to removing the gudgeon pin? I dont wanna beat on it too much. Removed circlips. It wont tap out easily.

What do the experts think?

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos. UPDATE

I'm not an expert but on Nortons I wrap a rag soaked in boiling water around the piston for a minute or two. It usually allows a light push out if nothing has picked up.

Re: Is this normal? with Photos. UPDATE

There is a tool, essentially a band of steel with a hole for the gudgeon pin to exit. On the opposite side is a bolt that acts as a press and pushes the pin through without any damage to the con rod or big end.....

Try Frost Auto Repairs website for specialist old style tools.

email (option): stinkypete80@hotmail.com

Re: Is this normal? with Photos. UPDATE

Hi Michael..Riks recommendation is the way to remove the pin. With the application of a little heat it will come out easily..As a matter of interest, all the headbolts are helicoiled on my M20..you won't have any problem with them...Ian

Re: Is this normal? with Photos. UPDATE

Do those measurements mean anything to you? I'm leaning towards having it bored to +60 and a new piston. I really dont know what Im doing though.

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos. UPDATE

Hi Michael, 82mm is a standard bore for the M20. In determining piston to bore clearance the piston should be measured across the thrust faces of the piston skirt..ie below the rings across the front and back of the piston. Piston to cylinder clearance should be .004"-.006" for a freshly bored cylinder.
Piston ring gap should be .008"-.012" for all three rings.
Niether the Army standards book or BSA manuals are totally clear about the total amount of combined piston and cylinder wear that is acceptable.
I take the mid limit figure for the piston to bore clearance in a new engine(.005") as the optimum. If the piton to bore clearance is at or exceeds .015" in a worn engine I will rebore it.
Your engine is on a standard bore so the next rebore would be to +020" assuming your bore is currently under that size...Ian

Re: Is this normal? with Photos. UPDATE

Thanks Ian,

That really helped clarify what Im working with. With this in mind, the greatest number for piston to bore clearance is .012". I get between .010" and .012". I will add a thou. for the sake of argument. Thats .013". Which seems pretty close to requiring a bore and piston.

Now with that said, do you think .013" clearance would account for the blow-by? I also measured no more than .012" ring end gap. Im just curious... maybe a fresh set of rings might get me back on the road through the summer?

As usual an attempt to solve one thing (head gasket leak) is leading to far more than I bargained for. Would love to think I could get by with a set of rings...

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos. UPDATE

Hi Michael, I won't go into all the figures for bore and piston wear detailed in the Standards book and BSA manuals as it can get a bit confusing. Suffice to say that one possible interpretation of the figures allows for a higher degree of wear than I outlined in the last posting. Taking the total possible bore clearance based on minimum possible piston size and maximum possible bore size as outlined in the standards book results, in my opinion, in an excessive running clearance.
The books state a maximium bore size and a minimum piston size but do not specifically state whether it is acceptable to run the two extremes together.
If for instance you had the max. bore size but with a new piston fitted that would be completely a different clearance to the same bore with the minimum size piston fitted to it.
Wear limits as indicated in my last posting are therefore what I have concluded are acceptable maximums over the years.
Based on that you may get away with a new set of correctly gapped rings.
Before fitting new rings carefully remove any carbon deposits that have built up at the top of the bore and remove any wear ridge (if present.)
Bear in mind as well that it can take up to a couple of hundred miles for the new rings to bed in fully and seal correctly.
I noted in your previous posting you mentioned you broke a ring removing it...was that the oil scraper ring?..and was it tight in the piston?...if it was this may have been at least a partial cause of the excessive oiling....Ian

Re: Is this normal? with Photos. UPDATE

If a correct ring size for the bore has a too large a gap, I always get rings for the next size up and gap them down to the min gap for the bore. This way you can get a tight ring on a worn bore saving you a rebore. On a bore this size the difference in the radius is negligible.

email (option): horror@blueyonder.co.uk

Re: Is this normal? with Photos. UPDATE

I agree, that was a useful 'dodge' I learnt many years ago as a teenager from an 'old boy' who lived near me.
BSA pistons go up in increments of .020" (std, +.020", +.040") In Michaels case he is on a standard bore so if an 'aftermarket' ring set from the likes of Hepolite can be sourced in a +.010" size all the better. Many of the aftermarket manufactures of the day produced pistons and rings in these 'in between' sizes (+.010"/+.030")and also went beyond the BSA maximum of +.040" to +.060"...Ian

Re: Is this normal? with Photos. UPDATE

While you have the barrel off, it is worthwile checking for play in the big ends. I started with a broken head steady, took off the head and sheared a bolt. Helicoiled the bolt, rebored to +40" and recut the valve seats etc. The big end does not so much float as flop. There is so much play, it may as well be made of rubber!
I am now in the process of a complete rebuild. Hope yours is OK.

email (option): stinkypete80@hotmail.com

Re: Is this normal? with Photos. UPDATE

i would try just a new set of ring as they say next size up and gap them to size and see what happens as it not difficult to get the barrel off if it doesnt work just the cost of the rings

email (option): roger.beck@node6.com

Re: Is this normal? with Photos. UPDATE

Where is the best place to get rings? And having only .013" bore to piston clearance should I buy +.020" rings?

I have almost no vertical play in the beg end. I do have about a half inch titling play measured from the little end. The side to side play is also very little. Only when I tilt the little end side to side do I have play.

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos. UPDATE

Hi Michael..Some directly side to side play is required...about .010"-.012"...but they will run ok with more. You should not be able to detect ANY up and down play..but getting the 'feel' for this can take some practice if you are not familiar with it.
The amount of 'tilt' is fairly minimal when a big end is newly fitted but is always apparent when the engine has covered some miles and is quite normal. I would go with a standard set of rings initially...Ian

email (option): ian@wright52.plus.com

Re: Is this normal? with Photos. UPDATE

Are the ring sets from dragonfly as good as any?

email (option): micran1234@yahoo.com

Re: Is this normal? with Photos. UPDATE

Personally, I have never had any problems with parts from there.

email (option): stinkypete80@hotmail.com

Re: Is this normal? with Photos. UPDATE

Hi Michael..I sent you an e mail regarding ring sets...Ian

email (option): ian@wright52.plus.com

Re: Is this normal? with Photos. UPDATE

OK, this is late in the game, and may sound silly, but is your crankcase breather clear? I had that problem on my MGA... Always check the cheap fix first is now my motto.

email (option): britool51@hotmail.com

Re: Is this normal? with Photos. UPDATE

Michael.
Sorry I am a bit late on this thread. On my WM20 the thread that is number 7 on the tightening order would not tighten, and the bolt looked just yours. This is the one right near the exaust valve, which made me think that the problem was caused by this being the hotest part of the engine.
I orderd a new bolt from Dragonfly. These are plated, which seems to add a bit to the size of the thread. It went in perfectly and torqued down to 28lb without any problem, without a helicoil.
Just thought you could try this before you buy a helicoil set and drill the barrel

Re: Is this normal? with Photos. UPDATE

I will try this. Im planning to buy new bolts anyways and a bottom tap. Can anyone comment on the best place to buy a set of head bolts?

email (option): micran1234@yahoo.com

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