No Compression
09-10-2009 | 02:33 PM
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From: EXETER, UNITED KINGDOM
No Compression
I'm not new to this game, in fact I've been playing with diesels for best part of 50 years, but I've never had a problem like this before.
I've just acquired a lovely Taifun Hurricane, boxed and perfect - looks like new. Beautiful green anodising, not a mark on it, BUT ... it's got no compression!
I thought at first maybe it was just dry, but a coule of drops of oil in the cylinder made no difference. The piston (yes it has one of those ..) goes smoothly up and down the bore like a worn out bicycle pump - the bearings feel like new, the reed valve makes all the right sucking noises - but no compression. I even thought that perhaps the contra piston was missing or damaged but it's there, where it should be, and a proper fit in the cylinder. In any case it's the piston seal that's letting the compression escape. I carefully unscrewed the cylinder from the crank case, and found little sign of the engine being run and the piston was like new - i.e. no staining, and no signs of wear on the sides. I have carefully re-assembled it and made sure that it has gone back together exactly as it should. The problem remains - you can turn it over 'compression' by just twisting the crank between your fingers, and it just blows bubbles out of the exhaust ports.
Now I've abused countless engines in my time and found that in fact, they are very hard to wear out. It takes a great deal of use and indeed abuse to get even halfway to the point where they are becoming difficult to start due to bore wear. Yet here is what appears to be a new, or very little used, high quality engine, in perfect external condition, that on the face of it appears to have totally a worn out bore. Doesn't make sense to me - anyone have any thoughts on this? Regards, Al.
I've just acquired a lovely Taifun Hurricane, boxed and perfect - looks like new. Beautiful green anodising, not a mark on it, BUT ... it's got no compression!
I thought at first maybe it was just dry, but a coule of drops of oil in the cylinder made no difference. The piston (yes it has one of those ..) goes smoothly up and down the bore like a worn out bicycle pump - the bearings feel like new, the reed valve makes all the right sucking noises - but no compression. I even thought that perhaps the contra piston was missing or damaged but it's there, where it should be, and a proper fit in the cylinder. In any case it's the piston seal that's letting the compression escape. I carefully unscrewed the cylinder from the crank case, and found little sign of the engine being run and the piston was like new - i.e. no staining, and no signs of wear on the sides. I have carefully re-assembled it and made sure that it has gone back together exactly as it should. The problem remains - you can turn it over 'compression' by just twisting the crank between your fingers, and it just blows bubbles out of the exhaust ports.
Now I've abused countless engines in my time and found that in fact, they are very hard to wear out. It takes a great deal of use and indeed abuse to get even halfway to the point where they are becoming difficult to start due to bore wear. Yet here is what appears to be a new, or very little used, high quality engine, in perfect external condition, that on the face of it appears to have totally a worn out bore. Doesn't make sense to me - anyone have any thoughts on this? Regards, Al.
09-10-2009 | 02:58 PM
#2
Senior Member
RE: No Compression
The engine probably is a result of someone combining two engines, and taking the biggest piston with the smallest cylinder. This leaves you with the smallest piston in the biggest cylinder. A bargain indeed! A very good showcase engine at best, if it is free of blemishes.
09-10-2009 | 03:50 PM
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From: EXETER, UNITED KINGDOM
RE: No Compression
You may be right PE - I really hadn't thought of that, but it seems like a lot of trouble to go to - and to achieve what? Surely all new engines from such a manufacturer would have fairly consistent good fits - or am I being naive? Anyhow, I'm stuck with the problem. The engine is 52 years old and in this condition, with box and docs, is worth repairing. I just need to find somebody who has the facilities to machine a new piston, I guess ...
09-10-2009 | 03:54 PM
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From: Montezuma
RE: No Compression
If that engine had a cast iron piston, you may be able to get the piston to grow a couple of tenths by heat treating it. I used to do Super Tigre .15 pistons by heating them in the oven at 400 degrees then letting them cool naturally and could get enough growth to restore compression. Sometimes even had to break in the p&l fit again. I'm sure that some metalurgist might have a different idea but you might not be out totally yet. Good luck.
09-10-2009 | 05:00 PM
#5
Senior Member
RE: No Compression
ORIGINAL: juxy2
You may be right PE - I really hadn't thought of that, but it seems like a lot of trouble to go to - and to achieve what? Surely all new engines from such a manufacturer would have fairly consistent good fits - or am I being naive? Anyhow, I'm stuck with the problem. The engine is 52 years old and in this condition, with box and docs, is worth repairing. I just need to find somebody who has the facilities to machine a new piston, I guess ...
You may be right PE - I really hadn't thought of that, but it seems like a lot of trouble to go to - and to achieve what? Surely all new engines from such a manufacturer would have fairly consistent good fits - or am I being naive? Anyhow, I'm stuck with the problem. The engine is 52 years old and in this condition, with box and docs, is worth repairing. I just need to find somebody who has the facilities to machine a new piston, I guess ...
The hurrican normally has very tight fits when sold, and this trick is normally not needed.
The cast iron piston is made of meehanite, which is sort of malleable cast iron. You can take the piston out, and make a punch that fits theinside closely. place thepiston bottom on a flat steel surface, and use the punch to hammer (expand)the piston bottom. A few microns (0.001mm) can be gained that way, enough fora re-lap fit. Do not use diamond grit on a cast iron piston though. It is hardly impossible to get the grit out of the iron pores later. So better use grit that dulls quickly if you lap the piston together with the cylinder.
The heat cycle growth of the iron is dearly needed during the running in process, so I would prefer to not use it to get thepiston to fit in the first place.
09-10-2009 | 11:24 PM
#6
My Feedback: (1)
RE: No Compression
ORIGINAL: juxy2
I'm not new to this game, in fact I've been playing with diesels for best part of 50 years, but I've never had a problem like this before.
I've just acquired a lovely Taifun Hurricane, boxed and perfect - looks like new. Beautiful green anodising, not a mark on it, BUT ... it's got no compression!
I thought at first maybe it was just dry, but a coule of drops of oil in the cylinder made no difference. The piston (yes it has one of those ..) goes smoothly up and down the bore like a worn out bicycle pump - the bearings feel like new, the reed valve makes all the right sucking noises - but no compression. I even thought that perhaps the contra piston was missing or damaged but it's there, where it should be, and a proper fit in the cylinder. In any case it's the piston seal that's letting the compression escape. I carefully unscrewed the cylinder from the crank case, and found little sign of the engine being run and the piston was like new - i.e. no staining, and no signs of wear on the sides. I have carefully re-assembled it and made sure that it has gone back together exactly as it should. The problem remains - you can turn it over 'compression' by just twisting the crank between your fingers, and it just blows bubbles out of the exhaust ports.
Now I've abused countless engines in my time and found that in fact, they are very hard to wear out. It takes a great deal of use and indeed abuse to get even halfway to the point where they are becoming difficult to start due to bore wear. Yet here is what appears to be a new, or very little used, high quality engine, in perfect external condition, that on the face of it appears to have totally a worn out bore. Doesn't make sense to me - anyone have any thoughts on this? Regards, Al.
I'm not new to this game, in fact I've been playing with diesels for best part of 50 years, but I've never had a problem like this before.
I've just acquired a lovely Taifun Hurricane, boxed and perfect - looks like new. Beautiful green anodising, not a mark on it, BUT ... it's got no compression!
I thought at first maybe it was just dry, but a coule of drops of oil in the cylinder made no difference. The piston (yes it has one of those ..) goes smoothly up and down the bore like a worn out bicycle pump - the bearings feel like new, the reed valve makes all the right sucking noises - but no compression. I even thought that perhaps the contra piston was missing or damaged but it's there, where it should be, and a proper fit in the cylinder. In any case it's the piston seal that's letting the compression escape. I carefully unscrewed the cylinder from the crank case, and found little sign of the engine being run and the piston was like new - i.e. no staining, and no signs of wear on the sides. I have carefully re-assembled it and made sure that it has gone back together exactly as it should. The problem remains - you can turn it over 'compression' by just twisting the crank between your fingers, and it just blows bubbles out of the exhaust ports.
Now I've abused countless engines in my time and found that in fact, they are very hard to wear out. It takes a great deal of use and indeed abuse to get even halfway to the point where they are becoming difficult to start due to bore wear. Yet here is what appears to be a new, or very little used, high quality engine, in perfect external condition, that on the face of it appears to have totally a worn out bore. Doesn't make sense to me - anyone have any thoughts on this? Regards, Al.
Al,
I'd heard of cases similar to your own, and then it happened to me. I got a well cared for Oliver Tiger Cub off a friend who had stored it away in the mid 60's when he gave up 1/2 A team racing. Compression was way down compared to it's previous state. We put it down to acids from the fuel residue eating away at the 1/10000 of an inch seal at the top of the piston. It came good with a new piston. There arn't a lot of preservative liquids that you can put into an engine that will be effective for decades, and it raises questions about the best method of long time storage for valuable engines. Perhaps in pieces with the piston assembly and the liner in seperate air tight containers?
Ray
09-10-2009 | 11:38 PM
#7
RE: No Compression
ORIGINAL: pe reivers
Do not use diamond grit on a cast iron piston though. It is hardly impossible to get the grit out of the iron pores later.
Do not use diamond grit on a cast iron piston though. It is hardly impossible to get the grit out of the iron pores later.
To test the fit are correct: The piston will go tight into the sleeve when the parts are without oil and with oil the piston will go easy into the sleeve.
The sleeve must be tapered then the piston will go tight in near TDC, it will keep compression while the engine are cold and make engine starting easier. Under working temperature, the sleeve will be parallel.
09-11-2009 | 12:04 AM
#8
RE: No Compression
ORIGINAL: juxy2
...The problem remains - you can turn it over 'compression' by just twisting the crank between your fingers, and it just blows bubbles out of the exhaust ports.
Regards, Al.
...The problem remains - you can turn it over 'compression' by just twisting the crank between your fingers, and it just blows bubbles out of the exhaust ports.
Regards, Al.
Try to start it by flicking it hard. If necessary even resort to a starter (prime only, no tank yet). If it fires a prime, add a tank and go from there.
I have a MARZ that had no compression from start. The compression grew as the engine ran (probably part castor seal, part stress relief).
George
09-11-2009 | 01:57 PM
#10
Senior Member
RE: No Compression
A friend thought the contrapiston was too tight in one of my ST G50-15's and decreased its diameter to where it leaked like a sieve. We heated it up with a torch, nowhere near starting to glow. I am still working on it with 400 sandpaper to get it to fit in the cylinder again. I'd definately try heating your piston to see if it will grow.
