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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: Jules on March 22, 2015, 04:54:40 PM
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I had always planned to do a compression test on my 'new' (to me) bike to see what sort of condition it's in. The bike has done about 92,000 miles. The first owner was a BMW mechanic, the second owner was not so fastidious (had the bike a couple of years) and then I'm the third owner. It's only going to be used for enjoyment, not main transport.
When I bought the bike the previous owner rode it ~80 miles to my house (as I don't have a license yet), so I'm not too concerned about the condition, as it can't be that bad.
I warmed the bike up, then shut it down and pulled off the cover plate, and the HT leads, marking them for each cylinder as I went. I extracted the plugs and got my new compression tester out of it's box. Which is when I realised there was no 12mm fitting. Only 14mm.
I've ordered a 12mm to 14mm adapter for a compression tester off ebay, so hopefully I will get a chance during the week to retry.
As I had the cover off the coils to mark both ends of the HT leads, I did notice that the number three HT lead was way longer than it needed to be. So much so that it had to be doubled back on itself to take up the slack. I'm guessing this is a number 1 cylinder HT lead that someone must have used as a replacement for a number 3 cylinder lead? A bit odd, but all seams to run ok.
I put it all back and ran the engine to make sure I hadn't messed up the HT lead order, and all worked as expected.
I did notice something else a little odd, that leads me to think my crankcase breather is blocked. With the engine running, if I open the engine oil filler the engine speed drops slightly. Not by much, but you can hear it. Holding my hand over the filler I can't feel any pressure there, but putting the cap back on, the engine speed rises.
Anyway, what sort of figures should I be expecting for the compression on the cylinders? I guess as the engine is on its side, there's no point doing a wet compression test?
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The #3 ignition wire is the longest. I think there's a UK ignition lead manufacturer that makes a #3 cable without the slop, but everybody else uses the OEM lengths AFAIK.
Spark plug/cylinder order is the same as coil order: #1 - #2 - #3 : front-to-rear.