blown base gasket nsr150sp

[ace222]

Hi guys-new to the forum / forums of any kind.

purchased my NSR 150 about 6 weeks ago. had 14900 k on it at the time and just had a full top end rebuild by the dealer i bought it from. today, about 2800km later i took it in for a service at a local workshop. being cautious i took the odomoter reading and know they did about 35km on it during the service -is this normal? up till now bike has been perfect and love it to death. get it back from service and report is that it has blown the base gasket (this seems strange to me as i would of thought this would have been new from the rebuild) however their explanation is that the previous owner has replaced the original air box with a performance part and as such the 2 air hoses out of the engine have been blocked with bolts causing air to go down and blowing the base gasket. it also has a fuel and oil leak which is clear on start up as you can really smell it - again previously no smell. i'm pretty level headed and understand shit happens but i get the distinct feeling im being screwed. my riding style has been very gentle as i am new to motorcycling, was cautious to run the bike in after the rebuild and also i only use it as a commuter to uni and haven't been over 80km'h letalone near redline. any advice, comments thoughts etc would be much appreciated as i'm not that mechanically savvy but have a basic grasp and certainly am not a fool.

at this stage i'm planning on getting a second opinion on it from another mechanic.

again thanks and sorry for the longwinded post

[BlackCatPhotography]

Hmmm wouldcertainly be asking why they needed to do 35kms on your bike, that's nit normal at all.

[SP1RITED]

Sounds dodgy, best to get that second opinion methinks . . .

[BlackCatPhotography]

Oh and tell the first shop you will be seeking a second opinion on it too, but that is a very good idea to have a second mechanic look it over, as what you have posted is certainly not normal.

[darkfibre]

Take what you just posted to the dealer who rebuilt it 2,800klms ago and get their opinion (take the fault reports with you)

[Halo_2]

Sadly you know which dealership to take it to, the hard way

[Loud]

Had to check that you didn't live near O'Connor in WA with a story like that.

1. What did they do for the service? I'm thinking a plug and maybe a gearbox oil change. Neither would create the issues you described - if it's gearbox oil that's leaking then that would indicate two separate issues, unlikely to occur after a 35km ride.
2. Why did they need to travel 35km? It shouldn't have needed to leave their workshop at all - a quick lap around the block if they were looking for something wrong at best.
3. Do they even know what a "Base Gasket" does? Or the 2 pipes that run to the airbox? Pipes to the airbox are either vacuum lines or emissions related (recirculated gas vapour). If they think blocking these 2 pipes created overwhelming pressure on the downstroke they should perhaps look up the function of a "Transfer Port" and look at the ones in your barrel to understand why they're wrong. If they think it affects the upstroke you should perhaps ask them why the damage was to a gasket that isn't between the piston rings and cylinder head, where combustion occurs.

In summary - Bolony. As recommended above, take it to the shop that rebuilt it initially.

On the plus side, it shouldn't be too expensive to fix. Except if you're on a shoestring budget as a Uni Student. But if you mention that you noted they rode it 35km you'd hope they'd contribute to the repairs.

Best of Luck, I know how you feel.

[ace222]

cheers for the timely and thorough responses. appreciate it. nah i'm not in WA at all - in Seacliff of SA - but i couldnt find any local sa forums for some reason and this forum seemed to have the most credibile responses when i was searching around so i crashed the WA party

dont much plan on going back to this shop - talked to a few local riders today and they've had similar experiences with services turning into sceptical blow out repairs

- yes they changed gear box oil and topped up the coolant levels. aside from that they did a few things at my request - tightened up my step kit and i asked them to give the bike a quick once over as i'd just purchased it and wanted to know what kind of shape she was in independently from the original dealer - we know how that turned out...

also out of interest- i have sort of noticed since i switched to motsul 710 ester from the shell fully synthetic they used in the original dealer i've been filling up the 2stroke resevoir a little less? would this support a blown base gasket?

will be putting the bike in the back of the ute sometime next week rather than riding it in to the original dealer - just in case there is something substantially wrong and i do any more damage.

after that i'll see what they say and see if i need to get another mechanics opinion.

i'll let you know how it all goes once i've taken it in!

[g0zer]

report is that it has blown the base gasket (this seems strange to me as i would of thought this would have been new from the rebuild) however their explanation is that the previous owner has replaced the original air box with a performance part and as such the 2 air hoses out of the engine have been blocked with bolts causing air to go down and blowing the base gasket. it also has a fuel and oil leak which is clear on start up as you can really smell it - again previously no smell.

is the fuel/oil leak from the base gasket? its a two stroke, that base gasket is sealing the crank case which is full of air fuel oil mixture under a positive pressure.

after the engine was rebuilt, was the barrel ever re-torqued? gaskets can compact the first time a motor is spun up, and things can come loose. most manufactures have got their shit tight these days tho, and things dont tend to come loose provided they are assembled exactly to the manufactures specification.

riding a bike 35km doesnt blow the base gasket.

incorrect/inadequate torquing of the barrel nuts, recycling old base gaskets, failing to use correct sealant (if specified) during assembly, scratches or damage to the interface between the base of the barrel and engine case, overheating the motor due to incorrect tune caused by modifications to air intake system- these things cause base gasket failure.

maybe cos you dont ride the bike hard the problem never manifested, i wouldnt expect a mechanic to thrash the shit out of their customers bikes during test rides but at the same time if you give an experienced motorcycle rider used to 150bhp your 20hp bike there is a good chance its going to get spun as hard as it will spin.

anyway so the base gasket is leaking, big woop. just retorque that fucking barrel and have a think about their comment re: modified airbox. maybe thats why there is so much extra km on the bike, cos they tried to retorque and took the bike back out and the retorque failed to correct the gasket leak. so they let it cool down, retorqued again and again failed. so they sat down and had a think about why its not sealing and have come up with a theory. maybe they are right, or maybe not. the base gasket is leaking for a reason, and it sounds easier to unblock those holes than to remove the barrel and fit a new gasket. try the 5 minute solution first and if that doesnt work then try the 2 hour one. except they can't try the 5 minute solution cos the OEM airbox and plumbing is no longer there. i dont know if that would cause the base gasket to blow, i dont see how it could but im not familiar with the nsr150.

also you have only paid them to service the bike, so now the time you have paid for is up and they have given the bike back to you which some comments. look at it from their point of view, they have been paid to change the fluids, tighten and adjust anything thats loose, safety check brake pads and whatever else is listed in the 15000km service interval and take it for a shakedown ride and its failed the shakedown ride. they havent built that motor or modified it so how is it their fault the base gasket is leaking?

if it was my bike i would want that carb opened up and check the jetting and needle clip position against stock. if the air filter/intake system has been modified to breath easier then the result is both more air going into the motor and less vacuum available to draw fuel up from the carb float bowls- this makes a motor run lean and it must be re-tuned to supply extra fuel to go with the extra air.

if a motor runs too lean it can run too hot and even suffer catastrophic damage such as seizures, pre-detonation and pistons melted through.

[NMBRPL8]

riding a bike 35km doesnt blow the base gasket.


if it was my bike i would want that carb opened up and check the jetting and needle clip position against stock. if the air filter/intake system has been modified to breath easier then the result is both more air going into the motor and less vacuum available to draw fuel up from the carb float bowls- this makes a motor run lean and it must be re-tuned to supply extra fuel to go with the extra air.

Riding the bike 35km doesnt blow a base gasket, but performing a minor maintainence service doesnt require riding the bike 35km either, there is no reason at all that they needed to ride that distance. If your theory on retighthening the barrle each time was even right, they should have called the owner to explain the issue they found and get permission to go ahead, not go for a 35km joyride. As for the fuel/jetting issue, if the airbox were removed and jetting left as standard, the bike would be unrideable, you would be very hard pressed to do any engine damage because it would be so so hard to get any useable power out of it, you would turn it off in disgust and walk away.
Fuel is not drawn into the engine via 'engine vacuum' as you suggest. It is drawn in by venturi, a type of localised vacuum effect but it works by the velocity of the air travelling through the carby, not from engine vacuum. If you needed engine vacuum, how would you supply fuel to an engine that isnt running to start it?? No vacuum, no fuel, no start, no start means no vacuum, means no fuel..... a cruel cycle.

Removed airbox does mean more air into the motor, which does make it run lean (more air in proportion to same amount of fuel the ratio is thrown off) but if the bike had previously been running well, whoever removed the airbox has almost certainly rejetted to suit. You said the bike was perfect before and you put nearly 3000kms on it, i think you can rule out dangerously lean running, it would have happened by now. If your still in doubt take a look at your spark plug to confirm.

Blown base gasket is pretty easy to check anyhow, there are a few methods. Have you ridden the bike at all yourself since then, is it difficult to start or run any worse, lacking power etc?
You described your riding style as gentle - this isnt really the best way to ride a two smoker! Not saying to thrash it, but they love to rev, and riding too softly may cause you more dramas than you think you are preventing...

[filbert]

Fuel is not drawn into the engine via 'engine vacuum' as you suggest. It is drawn in by venturi, a type of localised vacuum effect but it works by the velocity of the air travelling through the carby, not from engine vacuum. If you needed engine vacuum, how would you supply fuel to an engine that isnt running to start it?? No vacuum, no fuel, no start, no start means no vacuum, means no fuel..... a cruel cycle.

and how is that air velocity supplied to cause the venturi effect at the carb? could it possibly be the piston moving down sucking air through the carb? hence the term engine vacuum kind of a vicious (cruel?) cycle wouldn't you say? the system needs engine vacuum to work as previously stated.

don't bring a spoon to a gun fight g0zer has it right.


yes i see the irony in getting the knife to a gunfight saying wrong but it was deliberate

[g0zer]

If your theory on retighthening the barrle each time was even right, they should have called the owner to explain the issue they found and get permission to go ahead, not go for a 35km joyride.

what?

so you expect a mechanic to ask permission to retorque engine barrel bolts? checking torques is probably only the single most important thing to do during the first service on a fresh engine build.

no comment on your understanding of how a carb works or how fuel gets into a motor thats not running lmao- thanks filbert.

[NMBRPL8]

Not to ask permission to do so, but your hypothesis of doing it several times over and totalling 35km on test rides? Yeah, by that time, call and ask permission to carry on doing the work and charging the labour time, yes most definitely.

The way you phrased your previous comment made it sound like you were on about manifold vacuum sucking fuel out of the float bowl. Now your talking about the piston which is correct of course, but your comment about removing the factory airbox reducing vacuum to the carby float bowl? Sure, please elaborate on that for us, me and my spoon are waiting. How does removing the factory airbox reduce the vacuum then of the piston going up and down? Spoon feed me if you must.


*edit* Sigh now i will be torn a new one for referring to manifold vacuum. force of habit from working on cars so long. any chance of letting it slide? hell i still sometimes call fairings panels :p

[smeghead]

HowStuffWorks "How Two-stroke Engines Work"

[NMBRPL8]

Hmm OK i sounded like a right twat didnt i? lol SORRY ALL!!! Yes yes yes. Anyhow. Still wanting to know your theory on removing the stock airbox making less draw on fuel from the carby float bowl, i phrased my reply terrible in the first place but it was in reference to that part of your reply. Anyway, yes i can see how i looked like, without using the foul language, a right... spoon :p But seriously would like to know what your on about with the airbox comment.

I'll just be over here with my spoon digging a hole....

[NMBRPL8]

Howstuffworks, great site... good tv series now too. Suck sueeze bang blow, lovely.

[filbert]

Hmm OK i sounded like a right twat didnt i? lol SORRY ALL!!! Yes yes yes. Anyhow. Still wanting to know your theory on removing the stock airbox making less draw on fuel from the carby float bowl, i phrased my reply terrible in the first place but it was in reference to that part of your reply. Anyway, yes i can see how i looked like, without using the foul language, a right... spoon :p But seriously would like to know what your on about with the airbox comment.

I'll just be over here with my spoon digging a hole....

i thought it was a simple theory? it doesn't actually draw less fuel from the fuel bowl and vacuum doesn't decrease as a measurable factor but the ratios do change, otherwise you wouldn't need to rejet to solve a lean condition after changing your intake. The key wording was

if it was my bike i would want that carb opened up and check the jetting and needle clip position against stock. if the air filter/intake system has been modified to breath easier then the result is both more air going into the motor and less vacuum available to draw fuel up from the carb float bowls- this makes a motor run lean and it must be re-tuned to supply extra fuel to go with the extra air.

the way this works is that if the air velocity through the venturi draws fuel from the fuel bowl via mixture jet or emulsion tube at its maximum flow but the fuel to air ratio is still low then you need to change the jet.
More air is passing into the motor as he said, yes it still passes through the venturi but less vacuum as a percentage is available to draw fuel from the float bowls, if you increase the jet size to allow more fuel then all vacuum is available to draw fuel from the bowls.
I guess it could be poorly worded if you didn't work with 2 strokes all the time, or knew it as a theory rather than a practical application.

So anyway i was actually attempting to be polite/humorous rather than assume it to be anything more than a misunderstanding of terms but all engine vacuum manifold or otherwise comes from the downward travel of a piston with the exhaust path closed, be it by a poppet valve or a piston covering a port.
As for starting an engine not having vacuum, every downward stroke of the piston creates enough vacuum to draw enough fuel for combustion to sustain the next cycle, even on a kickstart the engine will generally cycle more than once so even if the vacuum of the first cycle wasn't enough to fire the next stroke should catch, this is also where the choke comes in by closing the air intake down it increases the vacuum available to supply fuel and why an engine can flood after only a couple of kicks.

[darkfibre]

theory on removing the stock airbox making less draw on fuel from the carby float bowl, i phrased my reply terrible in the first place but it was in reference to that part of your reply. Anyway, yes i can see how i looked like, without using the foul language, a right... spoon :p But seriously would like to know what your on about with the airbox comment.

Fuel is drawn into the intake air flow because of the pressure drop across the venturi. Any additional restrictions adding to the pressure drop (air cleaner/box) can and does change the mixture (same as a choke). This can be much more pronounced on Constant Velocity (CV) carbs.
If you are interested there are quite a few documented cases of consecutive dyno runs documented on the net.

[NMBRPL8]

Exactly. Think i even said that the ratios do change, in those words. But i simultaneously had a go at some bad phrasing, with more even worse phrasing of my own... lol

As far as carby airflow, is it really that more air flow passing through is reducing vacuum (across the emulsion tube) as a percentage or otherwise? I didnt think it was governed by quantity but by velocity, which is varied by the throttle slide or butterfly... To be honest i never got right into carby operational theory and maths, just the basics but stopped short of studying Bernoulli's principle.
Anyways i would have thought more air, same velocity (carby opening staying the same size and all, not getting bigger than it was) same size jet, hence too much air with not enough fuel. Wouldnt have thought that it was flowing less fuel, just the same amount but now getting more air than before, hence go up on the jet and or raise the needle.
Does this percentage thing work differently for fixed and variable venturi carbs?
Interested in this percentage of vacuum thing your talking about, never heard nor read anything like that before.

"poppet valve or a piston covering a port. " dont forget disc valves! mmm rotary disc valve. Even bettery yet rotating cylinder valve(RCV), i got to work on one in the flesh, quite an oddball but cool for the sake of it design.

[filbert]

Welcome to Coates International Ltd. yes we should totally get into a discussion of valve types look at my hand look at my hand!! no not that hand the one i'm trying to distract you with.

maybe i didn't simplify enough? or complicated it by trying to define the ratio or percentage? simplest form i can think of, if a choke closes the intake path and increases vacuum available to draw fuel then opening the intake path would decrease the vacuum available like g0zer said in the first place right?