South West Bikers | Motorcycle Forum

.....Every time I consider selling my 7 something goes wrong!

Last time i considered it my forks decided nope and spat the oil out so out they came and in to peak perf' for an overhaul.

This time took it for a ride yesterday, on my way back from a mates place in callington i hit false neutral (i missed a gear) then shortly after i noticed a missfire, limped it home pulled the tank off etc got the plugs out all ok, check the leads and trimmed the coil ends that were corroded.
Whilst there a stuck one of me digits in the spark plug holes and I thought number 3 seemed a bit low on compression anyway plugs back in fired it up with the tank raised up and still a miss there, pulled the leads one by one and number 3 is the problem hhhmmm, so swapped the plugs tonight but no difference. Then lifted the rocker cover to check my valve clearence and yes its way too low but not a case of no gap at all so its not a valve being held open.

Gotta wait now till i get the adaptor to do a compression test but so far its not looking good.

Anyone ever had or heard a prob due to missing a gear?

Mike

Can't say I'v heard of it causing that sort of problem, happens on mine all the time ( missed gear 1st to 2nd is a git for it) but never lost compression after?

I call it 'curse of the R6'

how come you want to sell it mike? you always give me shit if i say about selling mine haha!

thought about something different and more wet weather friendly, quite like a triumph speed triple but looks like i gotta fix the poxy 7 seven first.

If your valve clearances are too low you could end up burning the valve seats, which would lead to low compression... When you say you missed a gear, how high did it rev? Normally the rev-limiter would prevent any valve damage resulting from contact with the piston... Were you getting a good clean spark from #3 plug and lead?

It sounds like you're not afraid to get stuck in, how come you've left your valve clearances so long?

Yeah good spark on them all.

Swapped number 3 and 4 plugs over and no change.
Today the compression tester adapter turned up and did a comp test, before hand thou i did do a clearence check and as low as 0.08 on some so i know they really are way too low.
Anyway comp test revealed 1: 150 psi 2: 70psi 3: 40psi 4: 110psi that was dry did a wet test after and 1 and 4 improved yet 2 marginal improvement and 3 no improvement

Think its safe to say summit is wrong lol! possible head gasket between 2 and 3 but till i get the head off i dont know. Tried to take the engine out but the 2 rear mount bolts are seized solid, soaked em in WD40 and will leave them for a bit i think.

p.s to any mod's it might be an idea to move this thread to technical - sorry

Right managed to get one of the bolts out but the lower rear is being a pig, due to bleeding road works at the moment i cant get my van backed up to my garage to get the the oxy acetlyene on the job so for the mean time i've dropped the engine down at the front and pulled the head off.

I couldn't see any sign of the gasket gone but what i did find was an inlet valve has broken above the collet allowing it to contact and bend the valve in number 3 as for number 2 well pulled the valves out and its clear to see the seat has been blowing by.

Now to try and work out what to do i.e replace the whole lump or rebuild.

Gutted - should have done my clearances!

damn, sounds expensive

its looking that way.
Got to decide now do i repair mine - unlikely, do i fit a s/h head or engine? either way it'll have to go on the dyno for another set up so thats gonna be another £180 on top of what ever i do.
All cos i didn't do the valves, thing is it went extremely well before so what's it gonna be like when it running right!?

A couple of valves, a bit of lapping, and away you go - cheaper and better than another engine

Of course, that assumes you haven't hurt the pistons or anything else ...... but at least you know the condition of the engine you've got

agree with moose (for once) at least you know your engine and you never know what the hell you might buy off ebay or a breakers

Don't know what the chances are of finding a decent head at a breaker, whether they'd actually want to split one from an engine. At least you know a fair bit of the history of yours, and all the TLC it's had (sorry, couldn't resist...) A 2nd hand engine is an unknown - my mate Jon's CBR6 track bike threw a rod on its first dyno run after he bought it (and caught fire, did a proper job... ), but he found an engine on fleabay that has been as good as gold, and he got it for about £35! Yet there was always a chance thet it's be as bad as the one that blew up - best bet is to have a look round, on-line, in the comic, ring the breakers - good thing is that the 750 class isn't big in racing any more so there isn't a high demand for these engines....

I know what ya saying but...Inlet valve £20.66, Ex valve £40.50, head gasket £29.06, rocker gasket £26.16, piston rings £33.59 each piston!, cylinder gasket £22.68, valve shims approx £5 each and will need all 16!and thats not inc the cost of any guides and valve seals

As you can see it soon adds up to way more then the bike will soon be worth. sat and number crunched and well to rebuild my motor inc rings and de-gaze will be in the region of £450 plus guides if needed, whereas fit a good s/h head £200 or s/h engine £350 PLUS getting the dynojets set up again £180

I've decided i'm going to try to get a head ound a couple on e bag, get it skimmed, sort the clearances and get it back up and running will be fitting a minus 1 tooth front sprocket to go with the already fitted plus 2 rear.

Get your Dynojets set up again? If you're using the same carbs and exhaust as before, no problem, just bolt them on, stick petrol in and off you go... A lot of people probably neglect valve clearances, especially if changing them requires camshaft removal, and unfortunately you've learnt the hard way what the cost can be There's an old saying "A noisy tappet is a happy tappet" - got that from my dad who's into classic cars, but the theory's the same. Best of luck with your bids - don't have too much skimmed off a head if you win it, or you'll have to start messing around with cam timing (which, tbh, I'm not sure you'd be able to do with standard cams, the sprockets probably only bolt onto them in a single location, unlike race cams that you can dial in - if you reduce the cams' distance from the crank, the valve timing retards - probably not critically on a road bike, but remember that you'd be taking the valves closer to the pistons this way as well...)