MD1 pistonrings 2nd oversize

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lazytom

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can anybody direct me to a supplier of md1 pistonrings 2nd oversize (80,39 mm bore). sofar : asap negative, prior diesel ltd negative.
had a runaway situation on my mirror offshore, after 6 min being able to stall it. lower oil-ring cracked, otherwise no obvious damage.
so will reassemble the lump, got the cylinder honed and don't want to use the old rings.
any views on the possible cause of the runaway situation?
thanks
 
It might be possible to use a piston ring intended for another engine.
googling 80.4mm piston ring gives some possibilities.
You would obviously need the grooves to be the right size, although machining them bigger on a lathe is possible.

Some vintage vehicle buffs are very good at cross referencing part numbers.
You might find the piston was originally made by someone like Mahle and uses the same rings as a car or truck.

Good Luck.
 
RichardS said:
Possibly worn rings and bores leading to crankcase over-pressurisation and excess oil fumes being vented into the intake through the crankcase breather?

Richard
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Probably, but also look at the fuel filters. Blocked filters below the fuel tank were the cause of over running on the first Golf Diesel models. The owner of the boat next to mine had his “blow up” on the M6 and I learned that he had previously had the same symptoms that my Golf was showing (erratic idling). With difficulty I removed said filter and it was almost completely saturated with contaminants, not sludge. Apparently this encourages the pump just to keep asking for more fuel and so the revs.build until disaster.
 
lw395 said:
It might be possible to use a piston ring intended for another engine.
googling 80.4mm piston ring gives some possibilities.
You would obviously need the grooves to be the right size, although machining them bigger on a lathe is possible.

Some vintage vehicle buffs are very good at cross referencing part numbers.
You might find the piston was originally made by someone like Mahle and uses the same rings as a car or truck.

Good Luck.
Click to expand...


I have successfuly used oversize rings with the gaps adjusted to suit-4 thou per inch of bore for aircooled engines IIRC-to help get over worn bores. Many antique motorcycles had long strokes and conrods which applied great pressure and therefore wear to the upper front portion of the bore. Gapping the oversize rings in the worn bit was normally a great improvement on low powered engines


Try Thorntons for rings. I would be surprised if they cant help.

You will need to tell them bore size, ring thickness and radial depth. If you choose O/S rings, insert into the bore and square up with the piston skirt. The gap-or not-can be measured or the end of the ring filed untill the required gap is achieved. If the rings are cast iron, they will soon bed in to the bore. Steel or chromed top rings will take some time to bed in. Dont overdo the gap-as the rings bed in, the gap will increase .

If you are unfamiliar with handling piston rings, by an extra set.....................

Google is your friend here-lots of info there.
 
One thing you might want to do is change the breathing arrangement if you have a mucky exhaust and leaky rings. The original system had internal breathing where this comprised of crankcase gases passing from the pushrod space direct into the inlet port via a crude filter arrangement and this could have been the cause of the runaway as you may have had diesel dilution due to an extended period between oil changes. On a friend's engine we blocked off the internal breather with a metric threaded plug (actually used a Tecalamit grease nipple) and made an external breather to the inlet air filter and this ensured that it was relatively oil free air that was passed through to the cylinder. A connection was made by installing a swan neck pipe on a circular plate on the rear of the engine. The air passing through the pushrod space tended to pick up oil draining down from the tappets. With just a hone the engine started easily and ran cleanly for many years with less idk of running away.
The internal breather was probably used to get the engines through MCA etc regs for use in life boats.

The sump oil on these and many other small diesels becomes contaminated by diesel oil leakage from the crankcase mounted fuel pumps. This leakage is deliberate and allows lubrication of the pump plunger and is the reason for regular oil changes. Some folk can detect this by rubbing thumb and forefinger on he oily engine dipstick and sniffing it. Beware of there is a smell of diesel . It is this diesel contamination that causes runaway. If the spill leakage is large then you will not only notice that there appears to be zero oil consumption but that the oil level actually rises over time.
Hope you find scraper rings.
 
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thanks for all responses, certainly will check in future the oil and oil level more often (btw do you read the level with the dipstick fully screwed in and then out again or screwed out and then just dipped as far as possible?) and also consider rerouting the crankcase vapors.
what i forgot to mention in the original post, was that there was water in the oil (grey), how it got in is a mistery to me, head gasket ok, seals on the impellerdrive ok and no crack in head or cylinder noticable. is it possible that some cooling water got sucked in by the extreme high revs?
thanks
 
The oil in the crankcase might be due to water in the exhaust running back every time you stop the engine or excessive cranking with the sea water inlet left open and the water pumped through to the exhaust elbow back flowing as you appear to have ruled out the usual blown gasket cause. Is a water lock fitted in the exhaust and it is sized to deal with the volume of water that could run back in the exhaust when the engine stops.
 
richard,head gasket is perfect, was tempted to use it again, but still got a new one,, will see if i can check if the head is warped, but can't really imagine since it is only a single cylinder.
bilgediver, water backflow near impossible with a new vetus waterlock and a rise of aprox. 30cm behind it before going down to the waterline exit. excessive cranking is not on since i have only the handstart option and quickly out of breath.....
thanks again
 
lazytom said:
richard,head gasket is perfect, was tempted to use it again, but still got a new one,, will see if i can check if the head is warped, but can't really imagine since it is only a single cylinder.
bilgediver, water backflow near impossible with a new vetus waterlock and a rise of aprox. 30cm behind it before going down to the waterline exit. excessive cranking is not on since i have only the handstart option and quickly out of breath.....
thanks again
Click to expand...

One other possibility for the water is the water pump. If the water seal leaks then water should drip from a weep hole on the underside of the body midway between the pump bulge and flange. If this weep hole is blocked then this water can and sometimes does find its way to the crankcase. Check you seals and weep hole.
The seals are a standard seal for seawater duty and available from bearing suppliers for a few pounds. You can get seals with a double lip and I have used these when the shaft was slightly grooved and awaiting a new one. The annular groove in the water pump faces the pump and the annular groove in the oil seal faces the engine. The seals must be installed correctly and neither sitting above the weep hole. I put a spacer between them to ensure the weep hole can't be blocked.
 
When I had a Mirror Offshore, I bought a secondhand MD1 to use for spares and had great fun taking it apart and removing the bits. When I got down to the cylinder I found a small crack which because of its position could not be repaired at reasonable cost so rebuilding was not an option. After selling the boat I got quite a good return by selling bits on eBay and made a small profit as well as learning a great deal about small diesels.
 
Bilgediver said:
One other possibility for the water is the water pump. If the water seal leaks then water should drip from a weep hole on the underside of the body midway between the pump bulge and flange. If this weep hole is blocked then this water can and sometimes does find its way to the crankcase. Check you seals and weep hole.
The seals are a standard seal for seawater duty and available from bearing suppliers for a few pounds. You can get seals with a double lip and I have used these when the shaft was slightly grooved and awaiting a new one. The annular groove in the water pump faces the pump and the annular groove in the oil seal faces the engine. The seals must be installed correctly and neither sitting above the weep hole. I put a spacer between them to ensure the weep hole can't be blocked.
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+1. Happened to me with a MD2B. Common occurrence.
 
the puzzle continues: got in touch with thorntons on the advice of rotrax. they were requesting groove dimensions, the strange thing is that the three top rings are all 2mm
wide, but the 3 grooves are 2.55 / 2.1 / 2.5 mm . would that indicate that previous "marine-engineers" modified the width of the grooves but in the end couldnt get the right rings and settled for 2mm for all?? or is it standard that - especially _ the top ring has so much play(.55mm) ??
thanks again for all your interest and advice, will try codsduaflex.com tomorrow
lazytom
 
The 3 compression ring groves should be the same size and the clearance should be 0.06 to 0.09 mm. The clearances you have found are just going to allow excessive gas leakage. Maybe some one here has the right non butchered piston that they could pass on.

It could be that someone has previously turned the grooves to fit available rings and later some one purchased the correct rings and ignored the excessive clearance .
 
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