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Post by leon on Jul 21, 2016 13:01:23 GMT
Also, not sure why engine wouldn't stop when ignition was turned off? Only way to stop it was starve it of petrol. Sorry just realised H has already answered this. Cheers Clueless, have calmed down a bit now and will get in the shed later to start investigating.
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Post by triffid on Jul 21, 2016 14:04:17 GMT
RAC man sound like he doesn't know what he's talking about, that's an air leak all day I reckon. Stalling it usually works better than letting fuel die off, much quicker. So sorry for you after all that hard work.
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Post by leon on Jul 21, 2016 14:31:05 GMT
Yeah he was fixated on the fact the air filter had come loose, tried to point him to the oil leak/air leak but he wasn;t having it, and he lost interest in the cylinder when i explained how much needs doing to get access to it. Felt like he was looking down his nose at me cos I'm sure he sighed when I said I'd rebuilt it myself, but that might just be my lairy nature haha.
Wish I'd known I could've stalled it, assuming brakes would have held it! I know now anyway, thanks Triffid.
Is there any reason why it screamed when clutch was in or was in neutral, but when in gear I could control the revs with the throttle no problem?
I noticed the air filter had vibrated off completely, I'm hoping that was the clanking noise I heard just before the scoot jumped away from me.
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Post by dazzz on Jul 21, 2016 14:40:04 GMT
Omg , what a day. if I was you I'd whip the engine out and have a good look over it , and get it running and behaving right on the bench before you take it on the road again.
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Post by leon on Jul 21, 2016 14:58:00 GMT
You might be right Dazzz, better safe than sorry (sigh).
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Post by leon on Jul 21, 2016 18:08:16 GMT
Right I've part dropped the engine and taken the head off and this is what I've found: Piston: Cylinder head: Thats not good is it? This was a brand new piston, I've only ridden round the block for five minutes or so three times before today. Todays trip was a 14 mile round trip. First sign of trouble (screaming engine that wouldn't shut off) was after about 5 miles. I can't tell if I had oil/fuel leaking from the head AND the base of the cylinder, or just the head. But there was quite a lot of oil down the flyside of the engine (The flyside seal seems ok though so its not coming from there). Guess I fucked up eh? Also has the RAC guy made things worse or could the damage have been done? I'd had to try kill the engine for the third time when I stopped and called them.
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Post by tzsteve on Jul 21, 2016 20:44:21 GMT
heads blowing so lap it in wrap some paper aorund the barrel and tape it in place, so that you have a coller a couple of inches taller than the barrle. put a small amount of FINE grinding paste on the gasket face of the head, lower the head into the paper coller on the barrel twist the head back and forth a few times to get the gasket face naice and flat and clean, clean all the abrasive off that will stop the head blowing as long as you torque it down evenly
looks like the mixture is just a tad rich but that will not do any harm.
re the engine running on; with the barrel and piston in position check to see if you still get a spark when the engine stop button is pressed.
it could also be worth taking the flywheel off to see if you have signs of an oil leak / air leak from the fly side oilseal
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Post by leon on Jul 21, 2016 20:54:53 GMT
Thanks Tzsteve. I did try to lap the head and barrel after you suggested that method a few months ago. Probably didn't do it well enough.
There was more oil dripping down the casing than the head suggests, so I'm guessing the barrel wasn't sealed properly either - I didn't use any sealant, just the Ali gasket.
I've had the flywheel off and there's no sign of a leak from the seal.
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Post by kev on Jul 21, 2016 21:00:06 GMT
When I read ' passed mot '. I was chuffed for you , then I read further on and things got worse , feel for you mate as these scooters don't half try your patients , it'll come good in the end
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Post by Juan on Jul 21, 2016 21:00:48 GMT
Yeah, the old Polini 'heads are known to warp and blow. Reliable until it happens the first time and then just a nightmare. You can lap it etc. but it's only a matter of time before it happens again and it will be at the least needed window. I know you've already spent loads but I'd suggest you'd look at the new style replacement item for longer time results.
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Post by leon on Jul 21, 2016 22:02:12 GMT
Thanks Juan thats good to know. Will see what I can do. Having ridden the scooter a decent distance today I also realised I should have replaced the gear shift dog. Spoke to a guy my missus works with tonight who restores bikes. He said you always rush your first project cos you're desperate to ride it. Better to take your time and do it right with the right parts first time. A lesson learned. He also said that you should always have a scooter/bike to ride and at least one to work on, so I made sure my missus heard that bit.
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Post by henri on Jul 22, 2016 5:38:21 GMT
sounds like a sensible guy .also sounds like you had a "bad day at the office" too. dont be in a rush to replace the cruciform ,a first run with new cables settling in an stretching can give you gear selection problems,false neutrals etc .it might just of been adjustment needed . ignore the AA guy ,unless personally into scoots he wouldnt have a clue what a air leaks about , surprised he didnt ask were the socket for his fault-code reader/laptop to plug in was on the vehicle.thats actually happened to a friend of mine ,but was RAC. there not really mechanics anymore ,more mobile fitters .last weekend a mate had to get delivered by AA after a unscheduled stop coming to get some work done .AA guy was a scooterist with modded up px , the look on his face when after putting away his fancy trailer an coming over to get a signature .to find we'd already dropped the engine out,sussed the problem ,an were discussing a plan of action .priceless . H
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Post by leon on Jul 22, 2016 8:10:47 GMT
Cheers H.
So does that piston look normal then?
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Post by tzsteve on Jul 22, 2016 14:37:31 GMT
yep the off center burn and soot patern looks like a mismatch on the transfers very common on cheaper engines like scooters
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Post by GeorgeS on Jul 22, 2016 14:39:47 GMT
The piston crown looks ok to me. Have you clean the barrel or head up? If there was a head air leak I would have expected to see a tar-like oil deposit in that area and probably you'd see a lighter grey colour on the piston crown where it was running lean.
Like the others have said, it sounds like the RAC wouldn't know his arse from a hole in the ground when it comes to 2-strokes. A racing engine like that is certainly an air leak somewhere and the momentum and heat in the engine will cause it to keep running even with the ignition off, you have to stall it.
Check for oily deposits around the exhaust manifold where it joins the barrel and at the barrel base. Keep in mind how the air flows around from the fan inside the cowling and see if you can trace evidence of leaks. Also check your inlet manifold, if it's the standard steel type one with two fixings they can be a pain to seal up. Finally, if a standard carb is attached to this make sure it's on well, sealed and has the felt ring in the right place.
I've not read the whole thread in details, so forgive me if I'm repeating what others have said. It's well worth getting a leak tester if you can, or make one out of an inner tube (make one cut, connect one end to the exhaust outlet and the other to the carb manifold, secure with jubilee clips - quite difficult to seal fully) and use a foot pump with a pressure gauge.
Good luck, personally I think airleaks are the biggest problem you face & a frequent reason for breakdowns.
George.
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Post by leon on Jul 22, 2016 20:15:59 GMT
Thanks both, thats reassuring about the piston. Haven't cleaned anything yet, but had a peep at the barrel this aft without fully taking it off and it looks good, no scoring etc. I had a bad feeling about the RAC guy as soon as he arrived but hopefully no harm done.
Can't see any sign of oil near the exhaust manifold, can't be so sure about the inlet because of its proximity to the base of the barrel. Theres signs of a small leak at the head but my money is on the main problem being the barrel to casing join based on where the oil seems to have come from.
Felt ring - I've been putting it on the manifold after the bushing intake manifold goes on, so it acts as a seal between the bush, manifold and carb. I assume thats right.
Will clean it all up, and lap the head and barrel again. In fact I think you can see on the photos above where I did it before, and its clear I didn't manage to mate it properly.
I didnt use any gasket sealant before cos I was just following the stuff on Scooterhelp. Whats the best stuff to use you all reckon? And should I just use on base of barrel or on head/barrel joint too?
Thanks for all the input, commiserations(!) and advice, its much appreciated.
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Post by tzsteve on Jul 22, 2016 20:28:49 GMT
loctie copper silicon is pretty damd good, it does not claim to be petrol resistant but has a good reputation many use it on the head aswell, it`s great for exhaust gaskets.
threebond also has a very good reputation on general gaskets faces and seems to be petrol resistant.
for the head i have used loctite 270 (just a small smear keep it off the threads) that has worked well for me (recomended by dj webster)
for the head i`m now using loctite 510 as recomended by quatrinni cos thats what my kit is
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Post by leon on Jul 22, 2016 20:56:31 GMT
Thanks mate.
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Post by henri on Jul 22, 2016 21:30:25 GMT
permatex copper gasket goop for me on head joints , its stated as not for use were petrol is but good for turbo's ,so reckon they mean high petrol areas like carbs n such like . an wellseal for base gaskets nowadays ,use to just use grease n paper ,but 3 out of 5 tuners asked in scootering mag reccond it , an ive been using it for years on classic cars /water cooled head gaskets . H
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Post by leon on Jul 22, 2016 21:48:44 GMT
Cheers H. Will look for something from those suggestions.
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