fosdyke

Thanks guys but I think I have tracked down the culprit, though I am not sure why....... before reassembling engine as per Yoda's instructions I carefully checked all the valve clearances - sure enough 0 clearance on 1 & 4 inlet valves - infact the valves weren't even closing when they should - hence the low compression and blowback! I have now ordered 'undersized' shims from the dealer (the valves close with the shims removed) - the mechanic there seemed to think the valves might have stretched, and said he had come across it once before. What I am bemused by is why ALL of the valve clearances are less than I would have expected from an engine with nearly 50k on it - any ideas? The bike was a 'basket case' when I got it so I assuming all of the various bits came from the same engine - could be that the guy who abandoned it as a 'project' got 'new' cams which might explain the clearances issue. Will report back at the end of the week when I expect the shims to come in............in the meantime back to the w&d on the tank prior to spraying!!!

Welcome aboard......

Hi Looks like an early YB100 from what I can see - in which case you may well not find a negative connection for the battery as it would go straight to earth on the frame. Not sure about the bike in general but if it like the YB then it will run a magneto system for starting and charging - the battery is only a 'backup' for keeping the electrics (lights) running at low speed, so maybe it didn't have a battery? Sorry can't help more than that. Good luck.

Thanks for the reply.......................too late the things in bits now! Not too bothered this is about the third time I've had the head off during the rebuild - do want to get it right - that being said however I am on a reasonably tight budget, and on the basis that the bike only cost me £50 in the first place replacing all the rings @ £30 a set would have more than doubled the value (lol) ! The bike is a 92 Kwak GT550 straight 4 - so reasonably bullet proof (the other reason I only did half the rings). As to testing other things - you could have something about valve timing, it is a bit of a b***ger to set up 'exactly' and when you check the marks the degree or so it seems to be out could make all the difference - although why only on 1 & 4? I would have thought if the timing was out enough to cause a blowback in 1 & 4 it would do the same in 2&3?? It is the fact that I get a distinct blowback 'apparantly' on the compression stroke that seems to suggest valves or valve timing - I intend to fully check the clearances and shims on reassembly - maybe the valves aren't closing completely on these two cylinders for some reason - I did have them all out to replace the valve stem oil seals and examine the faces. Bit intrigued about your comments about the exhaust - certainly isn't (wasn't) leaking but not sure how it could affect blowback - by putting the heel of my hand over the inlet manifold you get a good vacuum - but on 1 & 4 it is followed by a little backward pressure that I don't get on 2 & 3. Ahhh well back to the spanners.....

It is possible as the petcock is a bit rubbish - but there is no smell of petrol with the leak. Didn't get a chance to change the oil pump yesterday as was fully engaged in disembowling the Kwak! Maybe will get on to it in the next couple of days. Will keep you all posted - in the meantime keep the ideas coming!!

Hi Ebay is a possibility - or a bike breaker though you will pay top dollar for it. How rotten is the tank?

OK - update time..... Engine now in rather more bits than when I started - valves are all OK - NO LEAKS WHATSOEVER!! so just a little annoyed shall we say - back to more head-scratching, and a v careful reassembly tomorrow, can only think that blowback has something to do with the valves or valve timing....... :huh: :huh:

Another problem to test the 'grey cells' ........... The old faithful YB100 has been losing 2 stroke oil at a considerable rate when standing in the garage, the oil 'appears' to be coming from the rhs of the engine where the carb and oil pump are. There are no obvious leaks from any hoses or the 2 stroke oil tank - it just seems to 'weep' out via the carb. I am going to change the oil pump tomorrow to see if this makes a difference, but in the meantime anyone else got any ideas??

Thanks Yoda - I rather thought I would have to get the spanners out again just to make sure - I was concerned about a possible overlap. Off to the factors to get some carborundum paste tomorrow! And yes I roughed up the bores prior to reassembly.

Re-used old in same place - the valve seats looked good so I didn't feel the need to lap them in.

Only 7!!!!!!

Thanks for the reply - this is a rebuild so I don't mind taking apart to get it right - I checked the ring gaps and replaced 1 & 4 rings so I don't think it is a ring problem which is why I think it is more likely to be leaky valves. That and the fact (confession time here), that first time I put the engine back together I got the inlet and exhaust cams the wrong way around and there could be valve damage although I would have thought the valves would have worked in reverse order thus avoideing this? Just looking for a way of checking without resorting to the spanner!

Ahhh GOFF now you are getting into the whole philosophical debate on Women as people or objects and possessions! Personally I don't disagree with anything you say - My OH REFUSED to ride pillion with me - and went in posse with us on the trusty YB100 until she passed her test. I much prefer to rock up to a bike meet with OH on her own bike - and I know she does - she says it makes her more of a 'proper biker' not just a dolly!

Hi Just want to float this around the workshop - sorry not a Yamaha - but the principles should be the same. I suspect leaking inlet valves as compression on 1 & 4 are lower than 2 & 3 on a compression test. The engine runs reasonably smoothly but their is a slight amount of 'blowback' particularly through no1 carb intake. I have checked valve and ignition timing and these are OK, so I am looking for a way of testing for leaking valves without: 1. doing a leak-down test - i don't have the tools 2. tearing the engine apart - will do if I have to, but will be gutted if after, this is not the problem!! any ideas???

Live to ride is quite correct - same size wheel (and tyre) on SAME axle - what a numpty - should have got his number and posted him a copy of the regulations for 'homework'!!!

What test are you doing A2 or Big Bike? All examiners have their own peculiarities about what they consider to be important - with some it's observation, others road position etc etc you won't know unless you get to speak to a riding school who work in that area. In my experience with my friends examiners seem to be tougher if you are taking the Big Bike test than the A2, and harder on women! If you get on to the DSA site you can download PDF's of the test routes for your centre, but be warned there are a few, AND the examiners mix & match. BUT if you can definitely go there and familiarize yourself with the area, and particularly where the test centre is!! Apart from that try and ride as textbook as you can lots of observation, good road position - think ahead, and be positive - otherwise yes its a lottery! Good luck - let us know how you get on.

"Dress for the fall.............not for the ride" - and if you want a reminder (not for the faint hearted) visit the 'ride to die' website - preferably before eating! What is worse GOFF, is the Pillion Pollys are probably wearing helmets at least a size too big as well so they don't get 'helmet hair'! Don't know about compulsory gear, in my opinion there is far too much nanny legislation in this country - to me this is just COMMON SENSE - if you don't want to get a bad case of Road Rash - dress appropriately!!!!

Hi Where did you get these from - and do they do them for other bikes?

Welcome, welcome Great bargain.................grrrrr Now my latest project is nearly finished I am looking for another!

Hi Welcome aboard.........................mmmmmm we like Melissa!

Hi you could try a dealer if you can give them a frame and engine number, but your best bet is a new ignition lock and key from a parts supplier or ebay - I picked up one for £10 (around $20) from ebay for my Kwak. Good luck

Hi Check the wiring diagram thoroughly (if you have one) for an additional relay in the starter circuit - my Kwak had one which had suffered from water ingress - a quick clean up with some w&d solved the problem. Good luck

Hi can't disagree with any of the above - connecting to the 'earth' wire for the rear lights sounds like a good idea as long as they don't use a 'return via the frame' as your indicators did. Black is usual for earth but being ordinary lights it doesn't matter which wire you use.

Hi Unlikely to be oil - more like petrol/air problem. check the oil level either with the dipstick or the sightglass though just to make sure there is enough, if the bike has been standing you could be low, and running it for a short while will distribute what there is around the engine. No throttle response would indicate carburettor problem, or air leak at the inlet. certainly that couple with the slow fall to a stall I would strip the carbs again and throughly clean and blow out jets and airways. hope this helps.

Hahahahahahahahahahahahahahahahahahahahahahahahahahahahaha! Reminds me of trying to get the rear engine mount out of an XJ600 - even the biggest sledgehammer couldn't 'withdraw the rear engine mount bolt' - but we got the b***tard with an angle grinder!!!!!