Lucky Phil Posted April 15, 2017 Share Posted April 15, 2017 Please tell me more about getting the squish band right. The squish area is basically the area around the piston circumpherence where it comes close to the head at TDC. The width and shape can vary depending on the engine. The purpose is to take that fuel air mixture around this area and force it towards the centre of the combustion chamber as the piston approaches TDC on the comp stroke and therefore create turbulence to promote better burning and concentrate the mixture in the smallest area for a fast burn and more effective ignition. To achieve good squish you are aiming at a slight wedge cross section with the tight area around the periphery to squeeze the mixture into the centre. To achieve this you need the clearance to be around 1mm or 0.040". You need to account for piston expansion and rod stretch at max rpm. Any more than around 1.2mm is ineffective and any less than around 0.8mm a bit risky. Most older road engines will have more than 1.5mm and/or no real squish shape so basically ineffective. On a Ducati or Guzzi you can adjust the squish by varying the base gasket thickness and you may need to machine the chamber and piston to improve the shape. Sorry, a quick and dirty overview. Ciao 2 Link to comment Share on other sites More sharing options...
68C Posted April 16, 2017 Share Posted April 16, 2017 Good reply, I knew what the squish band was but never thought of checking or adjusting it. How do you know how much the head gasket compresses by, feeler gauges in between the head and barrel after it is torqued down? Edit: Just found this on a GasGas forum. http://www.gasgasrider.org/html/measuring_squish.html, I should have researched this first I sppose. Link to comment Share on other sites More sharing options...
Tinus89 Posted April 16, 2017 Author Share Posted April 16, 2017 Interesting reads about squish band! So, I'm going to steal my topic back: she is running! But.... It seems like the rattle is still somewhat there, but less. I will need to re-adjust the valves after a short run and then probably after some 1000km again. Should I also replace the oil after a bit? She does need a full tune-up though... The idle before the little drive around the block was steady as a rock, but as soon as I went driving, the idle was too low and rough, stalling each time I came off the trottle. After the drive she was sneezing and backfireing sometimes... Also, she has developed a fuel leak at the T-junction on the back of the injector... Not sure how I should deal with that. Are there seals in the plastic parts that are kept together with circlips? Link to comment Share on other sites More sharing options...
footgoose Posted April 16, 2017 Share Posted April 16, 2017 On mine, the 2 pieces held together with the large circlip are aluminum. There are no seals there. They just clip onto a flange to hold the fuel line t-junction in place. I haven't been any deeper, but it feels like if you pop that off the seal is under there. Link to comment Share on other sites More sharing options...
czakky Posted April 16, 2017 Share Posted April 16, 2017 Yes, two seals. One o-ring should be easily sourced, the other might be a bit more difficult. I personally never replaced them. Link to comment Share on other sites More sharing options...
GuzziMoto Posted April 17, 2017 Share Posted April 17, 2017 Good reply, I knew what the squish band was but never thought of checking or adjusting it. How do you know how much the head gasket compresses by, feeler gauges in between the head and barrel after it is torqued down? Edit: Just found this on a GasGas forum. http://www.gasgasrider.org/html/measuring_squish.html, I should have researched this first I sppose. From the factory the V11 motor has crap for squish. There is a large bevel in the head that give most of the available squish away. There are pistons from Mike rich that match this bevel, bringing back the squish. But they are hard to get as availability is limited. The stock piston does not match the bevel so there is little squish. I had a machine shop mill the heads to gain most of it back, i.e., remove most of the bevel. Then I had the cylinders machined to where the pistons were near flush with the deck height. This set the squish at just over the thickness of the head gasket, tight by most peoples standards but more than we would run on a race motor. Squish and compression are your friend, but they won;t pick you up at the airport. Link to comment Share on other sites More sharing options...
Chuck Posted April 17, 2017 Share Posted April 17, 2017 Squish and compression are your friend, but they won;t pick you up at the airport. Dang! That's always been an issue.. Link to comment Share on other sites More sharing options...
swooshdave Posted April 17, 2017 Share Posted April 17, 2017 Squish and compression are your friend, but they won;t pick you up at the airport. Dang! That's always been an issue.. Maybe not at the airport but I think I met those two at the airport bar... Link to comment Share on other sites More sharing options...
Tinus89 Posted June 20, 2017 Author Share Posted June 20, 2017 So, after discussing a different (electrical) issue on this great forum! here: http://www.v11lemans.com/forums/index.php?showtopic=19943&page=9&do=findComment&comment=222199, I would like to re-start this discussion again. I've noticed the metallic sound is still increasing. Here is a video where you can hear it, but I will try to make a better one soon: https://www.youtube.com/watch?v=LnTi_vtetIM The sound changes/goes up with rpm. Also, it sounds like it is originating more from the right cylinder, so I want to focus on that. I have checked (and let a specialist visually inspect) every moving part in that cylinder, which are all OK. Now my focus is on the head, which is the only thing I have not disassembled. Some points for discussion: - Can a loose valve seat be observed from the bottom with the valve closed? - Could a loose valve guide (or anything else there) create a sound like this? - Could something cause the valve to close "late", which then causes the cam follower to loose contact from the cam momentarily, be pushed back with speed, causing the sound to be coming from right centre of the engine (cam follower hitting camshaft hard), contrary to the head? Link to comment Share on other sites More sharing options...
luhbo Posted June 20, 2017 Share Posted June 20, 2017 Check the exhaust manifold gasket. Ed.: ...although the VIMEO video from last year sounds different. Anyway, mine sounds best when I have my ears plugged, means I could hear all I want in such videos. It's a rattly lump this engine The RM Candy Red is quite nice by the way Link to comment Share on other sites More sharing options...
Tinus89 Posted June 21, 2017 Author Share Posted June 21, 2017 Check the exhaust manifold gasket. Ed.: ...although the VIMEO video from last year sounds different. Anyway, mine sounds best when I have my ears plugged, means I could hear all I want in such videos. It's a rattly lump this engine The RM Candy Red is quite nice by the way How do I check it? Just feel for leaks? Re-tighten it after it has been hot once? Change the gaskets preventively? The exhausts have been off about 6 or 7 times... Thanks! The Candy Red is why I fell in love with this bike:) Link to comment Share on other sites More sharing options...
luhbo Posted June 21, 2017 Share Posted June 21, 2017 You could listen carefully, now that you think it might be the gasket. That would be check enough. And then replace them anyway. They're cheap and easy to get by. Blowby at this point is a very strange, irregular and high pitched twitter. Link to comment Share on other sites More sharing options...
footgoose Posted June 21, 2017 Share Posted June 21, 2017 Check the exhaust manifold gasket. Ed.: ...although the VIMEO video from last year sounds different. Anyway, mine sounds best when I have my ears plugged, means I could hear all I want in such videos. It's a rattly lump this engine The RM Candy Red is quite nice by the way How do I check it? Just feel for leaks? Re-tighten it after it has been hot once? Change the gaskets preventively? The exhausts have been off about 6 or 7 times... Thanks! The Candy Red is why I fell in love with this bike:) I use a short length of garden hose. One end to my ear and the other used to probe for leaks. When you get near the leak you'll hear a distinctive tapping, it'll be obvious. You can do the same thing with a screwdriver to check location of internal rattles. Put the handle end to your ear and touch the other end to the "area" of concern. The noise will amplify. Link to comment Share on other sites More sharing options...
Tinus89 Posted June 21, 2017 Author Share Posted June 21, 2017 In thinking about replacing the gasket anyway, which parts should I actually order? The gasket of course, but if you look at the below picture, I don't think in the current setup, the spacer - circled in red - is installed at all? What's it's function? Link to comment Share on other sites More sharing options...
Chuck Posted June 21, 2017 Share Posted June 21, 2017 If it's not, you have nothing to seal the gasket.. Link to comment Share on other sites More sharing options...
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