Oil consumption on my 92 Mk1 was getting silly, an 1100 mile long weekend to Ireland got through 1.8 litres, and people were starting to comment on the amount of smoke it was producing under acceleration.
Prime suspect was the piston rings, and £35 to M&P for a compression tester (needed to unbolt the radiator and drop it foreward a bit to get enough access for the tester) showed over 1.5 bar increase in pressure when I bunged some oil down the barrels, a sure sign of ring problems I'm told.
Apart from the cam chain tensioner being behind a engine mounting bracket it's pretty easy to get the head off a Mk1. Exhaust, fuel tank, airbox, carbs, radiator and thermostat housing all need to come off first, then you can get the valve cover off. Turn the engine to TDC (the Mk1 is a 360 degree crank unlike the Mk2 which is 270), take out the cam chain tensioner and front guide, take off the cam sprockets and oil banjo bolt and the head unbolts and lifts off. After struggling to get the block off for 10 minutes, undo the coolant union on the front of the block and the head pops off easily. 2 circlips on the ends of the piston pins and the pistons pop off.
My pistons were filthy, but cleaned up nicely with some Mr Muscle oven cleaner and a toothbrush. The head and barrels I took down to a local bike shop who sent the barrels off to be honed, cleaned up the head, and leak tested all the valves. I also ordered all the new gaskets and o-rings from him. Took him a couple of weeks to get everything and the total cost was about £270 I think.
New piston rings went on easily enough but getting the head on (with 2 new o-rings and a new gasket) took a while with a mate helping, the bottom of the barrels is chamfered to make it easier but it's still a struggle, and the only piston ring compressors I could find didn't open fully so are only any use if you've disconnected the con rod from the crank rather than from the piston (I'm told this is the usual method in cars). Once the barrels were on, the head went on pretty easily with a new head gasket. Getting the cam sprockets on and lined up properly is a bit fiddly but not too bad. I got a new seal for the valve cover, but probably didn't need it, and found that you need to stick the seal to the cover with a few dabs of sealant or otherwise it falls off when you're getting the cover in to position. From there it's a fairly simple matter of refitting all the ancillary bits (getting the throttle cables on the carb is far from simple though)...then taking the valve cover back off when you find the cam chain front guide still sitting in a crate in your garage. I damaged an o-ring putting the coolant union back on the front of the block, so had to wait a week to get another one from Yam at the rather high price of £1.75 (nowhere near me seemed to stock sensible sized o-rings). New oil and filter, plus the o-rings in the filter housing (get the filter from Halfords, it comes with the large o-ring), and some coolant and it was pretty much done. My exhaust is a bit knackered and I needed some sealant on some of the joints, so I actually used a high temperature sealant instead of exhaust gaskets, mainly because I'd completely forgotten to order them and couldn't be bothered to wait another week.
So far I've only done about 50 miles, using cheap Halford own brand oil and keeping it to about 5000 rpm without too much hard acceleration. I intend to do an oil change before doing many more miles and then gradually start working the engine a bit harder for the next few hundred miles, but I'm moving house this week so it might be a while before I do this or use the bike much. It's worth checking the oil very regularly to begin with, it dropped very quickly in the first few miles, presumably a bit gets past the rings before they bed in and there's a lot of places in the engine for oil to go that it probably doesn't get to until the engine's running.
Total cost was probably around £350, something like £120 of that was the gaskets, and I could have saved some cash if I'd done the work on the head myself and found someone to hone the barrels rather than having the bike shop take a cut for sending them to someone else. Plus that included a few tools like the compression tester and a rubber mallet. In terms of the amount of time taken I reckon if I'd pulled my finger out I could have probably got it apart in a day and got it back together in another day, but because it's the first time I've done anything like that and I'm lazy and don't do weekend mornings in the garage in the middle of winter, it took more or a less a weekend to strip and another weekend to rebuild. Getting the head on and off is defintaly a 2 man job. I would class myself as reasonably technical but I'd never attempted any work like thisbefore. I learned loads, enjoyed doing it, and was suprised how easy it actually was.
Didn't intend this to be quite such a long essay, but hope it's of interest to someone. If you made it this far I've even included some pictures.
Pistons when they came out
And after cleaning
Head when it came off
Head after cleaning
Bike stripped down
