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Discussion Starter #21
Bring it here and I can help you adjust your valve clearances ;)
I'd almost put money on it your hard start problem is valve clearance being wrong. I don't even try to check them any more, I just go straight to adjusting the clearances if they have screw type adjusters and not shims.
Thanks Trials Rider, very generous of you! :LOL:(y)(y)(y)
(P.S - I'd love to come riding in Canada, winter and summer! That's on my bucket list!)

Yep, you might be right, valve clearances may still be well out. They are the screw type adjusters and I've tried setting them to 0.002 (Exhaust) and 0.003 (Compression) but I'm guessing I'm not the first person who finds getting them perfect or at least within tolerance is kinda tricky.

I've taken the centre and top caps out of the engine cover, turned the crank CCW to find TDC, but find that it does "Flop" past that a lot? If that happens, my understanding is that you can't "go back"? You have to repeat the 2 rotations CCW and get it to sit just on TDC on the compressions stroke? (I've read about leaving a heavy ratchet on the crank to hold it in place and not "flop forward"?)

REALLY subtle movement on the valve tappet on Compression. Hard to notice the difference at the first couple of attempts....and if they TIGHTEN up over time, how the hell are you supposed to know which is which, if they're both tight! :) Yep, I've put a pencil in the spark plug hole to see what the piston is doing, but that doesn't help does it? (because the piston goes up to the same height/point on both exhaust and compression strokes, right?)

I'm also wondering, if it's NOT a Piston/rings/cylinder issue, if it could be the decompressor. Either the Lever or Kickstart one?

(My 92 Manual shows a cable connecting the two, from the decomp lever at the top of the engine to the kickstart decomp and the bottom, but it's been removed from my bike. Don't think it ever had one when I bought it in.......1998! Whoa, long time ago huh :) I'm not sure if that cable missing is a problem or not.)

Anyway, compression tester coming today, so I'll test over the weekend and update........

Thanks again for your comments TrialsRider :)
 

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Just a guess because I haven't looked at the service manual for your bike but I would suspect valve clearance would be closer to 12 thou on the exhaust and 4 thou on the intake. Exhaust is subjected to far more heat so that valve stem grows ~3 times faster then the intake ever will.
... make sure you are setting the valve clearance on ignition TDC and not exhaust stroke TDC, I've done that before. The TDC mark you want to see is right after the intake valve has just completed closing and you are on the upstroke.

You can make a little wrench to hold the square head screw adjuster by just cutting a piece of wood stick about 3 inches long by 1/2" diameter, then thread a #2 Robertson socket screw into one end ;) poor man's square socket driver.



I don't suppose you know Jake Stapleton do you? He moved to Canada and rides at my place sometimes now.
 

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Discussion Starter #23
Just a guess because I haven't looked at the service manual for your bike but I would suspect valve clearance would be closer to 12 thou on the exhaust and 4 thou on the intake. Exhaust is subjected to far more heat so that valve stem grows ~3 times faster then the intake ever will.
... make sure you are setting the valve clearance on ignition TDC and not exhaust stroke TDC, I've done that before. The TDC mark you want to see is right after the intake valve has just completed closing and you are on the upstroke.

You can make a little wrench to hold the square head screw adjuster by just cutting a piece of wood stick about 3 inches long by 1/2" diameter, then thread a #2 Robertson socket screw into one end ;) poor man's square socket driver.
Thanks TrialsRider....... the Haynes Manual def says .002 and .003..........but arse about from my previous post typo.

So it's .002 Intake & .003 Exhaust. (I'll have to make sure it wasn't just a typo in the post and didn't set them arse about on the bike! haha :rolleyes:)

Are you suggesting .012 for exhaust and .004 intake?

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I'm pretty sure I had it on Compression stroke. I've read you should "Feel" a little (TINY) bit of play in all of the tappets on that stroke (cause the valves are all closed, right?)

And so if you're saying the other way I know is it's the "T" I see just AFTER "the intake valve has just completed closing" or in other words "rising UP"..........?

I'll have another crack at it today and make sure (as best I can) that valves look to be in spec, then check the compression.......

I don't suppose you know Jake Stapleton do you? He moved to Canada and rides at my place sometimes now.
Ha! I don't "know" Jake. We're not mates or anything......but anyone who reads ADB (Aus Dirt Bike) mag will know Jake Stapleton. He was their Enduro Editor for years up until a couple of years ago I think. Very Fast on a dirt bike. Say g'day to him for me, from all of us in Aus. ;)🍺(y)
 

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The .012 exhaust and .004 intake is for my 4 valve Honda motors, yours could very well be as per the Haynes manual, just seems a little strange.
I just watch for the intake valve to finish closing, then I know I am on the start of the compression up stroke and 180 degrees from TDC


Jake is riding a trials bike now as well as his extreme enduro (y) great fun to watch.
 

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Discussion Starter #25
The .012 exhaust and .004 intake is for my 4 valve Honda motors, yours could very well be as per the Haynes manual, just seems a little strange.
I just watch for the intake valve to finish closing, then I know I am on the start of the compression up stroke and 180 degrees from TDC
Can you elaborate on why you think it's strange? Where did you get the .012 and .004 from?

Yep, so by "intake valve to finish closing" you mean tappet rising UP, correct? Down on the tappet is open, up on the tappet is closed.

Jake is riding a trials bike now as well as his extreme enduro (y) great fun to watch.
I just got into trials late last year as well! Really enjoying it! And it's a lot harder than it looks! But great fun!
My enduro riding is a LONG way off extreme and I'm pretty shit to watch (haha) but I love riding single trail and can't wait to get back out there! I think my 18 exc-f 350 was one of the last enduro reviews Jake did with ADB after moving to Canada? Great bike, love it. :love:

103110
 

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Discussion Starter #26
COMPRESSION TEST RESULTS......

So, unless there's something else going on that i'm not aware of....the ol' girl is way down on compression.

About 100 psi on compression (should be 185 to 213 as per Haynes manual above)

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Just a tad over 40 with the decomp lever pulled in (should be 92 to 107 as per Haynes manual above - the only concern with the manual is that it shows Decomp pressure for the 1996 onwards only???)

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Either there's something else going on that I'm not aware of, or the valve seats / rings / piston / cylinder are kaput. (in that order?)

I did note some oil on the compression tester thread when I pulled it out, so it's apparent there's some leakage, somewhere in there.

The last work done on that engine was a fair while ago by a mechanic (obviously while i was far less adventurous)....... Top end rebuild and from memory, and they said it was at capacity for big bore Piston and rings for the block.....

So, my options are.....
  1. Pull the engine out and take it to a pro again for a rebuild OR
  2. Pull the top off myself and start to look at what's going on inside before I make a call on that, one way or the other.......
Let me put this out to the community. WHAT WOULD YOU DO? :D:rolleyes:
 

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give it a leakdown test. that will tell you if it's leaking anywhere.

adjusting valve clearances - adjust the inlet when you see the exhaust valve start to open. adjust the exhaust just as the inlet fully closes. if you want to see if the clearances are an issue with the starting, add a couple of thou and see if it makes any difference.
 

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What Brad said. Get yourself a good leakdown tester. If I had to choose between a compression guage and a leakdown (a/k/a cylinder leakage) tester, there is no question that it would be the leakdown tester. It is a very valuable diagnostic tool. I prefer the large, single-guage type, but they are not as common as the dual-gauge variety.

Try putting a few squirts of motor oil in the spark plug hole and kicking it a few times. Put the compression guage back on and check it again. This is called a “wet” compression test. Be sure to hold the throttle wide open when you are testing. If the numbers go up appreciably, it’s a ring sealing issue. Maybe because they are worn. Maybe because the bike has been sitting so long that they are dry or stuck. If you have enough compression to get it to run (which may require a sniff of starting fluid) you can retest compression and reevaluate the engine’s condition
 

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Discussion Starter #29
give it a leakdown test. that will tell you if it's leaking anywhere.

adjusting valve clearances - adjust the inlet when you see the exhaust valve start to open. adjust the exhaust just as the inlet fully closes. if you want to see if the clearances are an issue with the starting, add a couple of thou and see if it makes any difference.
Thanks Brad, I'll look into the leak down.....

Just so I understand what you're suggesting re "Adding a couple thou"...... so that means the "Gap" between tappet and valve head will be larger, which means the distance the valve actually Open, will be smaller, right? I'm interested to understand how that helps with starting?

Thanks again for your comment.......

What Brad said. Get yourself a good leakdown tester. If I had to choose between a compression guage and a leakdown (a/k/a cylinder leakage) tester, there is no question that it would be the leakdown tester. It is a very valuable diagnostic tool. I prefer the large, single-guage type, but they are not as common as the dual-gauge variety.

Try putting a few squirts of motor oil in the spark plug hole and kicking it a few times. Put the compression guage back on and check it again. This is called a “wet” compression test. Be sure to hold the throttle wide open when you are testing. If the numbers go up appreciably, it’s a ring sealing issue. Maybe because they are worn. Maybe because the bike has been sitting so long that they are dry or stuck. If you have enough compression to get it to run (which may require a sniff of starting fluid) you can retest compression and reevaluate the engine’s condition
Thanks TrialsRider, really appreciate the Troubleshooting steps! Especially the suggestion of the "Wet Compression Test" - I'll give that a crack. (y)

That was part of my concern with the Leakdown test, not being able to get it to start and therefore not being able to do the leakdown with the engine at operating temp.

That, and the fact that I don't have a leak down tester. haha. :) They range anywhere from $30 to $300 here in Aus so buying one is certainly an option, but I suspect the accuracy of the cheaper versions might be dubious, which kind of defeats the purpose?

So, a question for both you and Brad, "Is it completely dodgy to just stick your compressor on the spark plug hole at say, 80-100psi (or less to begin with, to be on the safe side) and then just listen/feel for where the air comes out?
 

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Looks like you found a problem.

I would recommend you tear that motor down to the bottom end gasket, it's not rocket science but you will want a 1/4 inch drive torque wrench. I think the problem might become obvious once you get inside there, it usually does.

What you are doing when you set the valve clearance is, setting it up so that once the motor is at normal operating temperatures, there is virtually no clearance between the cam and the cam follower because the parts have all expanded to where it is designed to operate.

Rode a lot today and more again tomorrow omg my muscles hurt. I need to ride a lot more and eat a lot more to get in shape fast, I'm having to really bend the knees and get low this year.

 

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You could put a fitting in the spark plug hole and pressurize the cylinder. You probably will hear some amount of air bleeding past the rings and into the crankcase. However, you won’t be able to measure the percentage of leakage. If a valve is not sealing, you may hear it. Whether you hear it over the air bleeding into the crankcase (and, unless the engine is in top shape, there will be some) is hard to say. It will probably run on 100 PSI. Make sure that the carb is clean and has fresh fuel in it. Give it a shot of starting fluid. If it has fuel, compression and spark (at the right time), it should make some noise.
 

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Discussion Starter #32
I would recommend you tear that motor down to the bottom end gasket, it's not rocket science but you will want a 1/4 inch drive torque wrench. I think the problem might become obvious once you get inside there, it usually does.

What you are doing when you set the valve clearance is, setting it up so that once the motor is at normal operating temperatures, there is virtually no clearance between the cam and the cam follower because the parts have all expanded to where it is designed to operate.

Rode a lot today and more again tomorrow omg my muscles hurt. I need to ride a lot more and eat a lot more to get in shape fast, I'm having to really bend the knees and get low this year.
Thanks TrialsRider, looks like you're doing just fine in that photo! (y)

Yep, I have a 1/4 torque wrench and, based on the below, I agree, a top end tear down is next cab off the rank.

Wet compression test produced nearly 150psi, (50% increase on previous 'dry' test) so hopefully it's just rings but we'll see......

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Thanks again and enjoy your riding! (Very jealous, I'm Sydney based and it's pretty hard finding places to ride at the moment, but soon, very soon (please!!!!) :)

You could put a fitting in the spark plug hole and pressurize the cylinder. You probably will hear some amount of air bleeding past the rings and into the crankcase. However, you won’t be able to measure the percentage of leakage. If a valve is not sealing, you may hear it. Whether you hear it over the air bleeding into the crankcase (and, unless the engine is in top shape, there will be some) is hard to say. It will probably run on 100 PSI. Make sure that the carb is clean and has fresh fuel in it. Give it a shot of starting fluid. If it has fuel, compression and spark (at the right time), it should make some noise.
Thanks upperb, Based on the above wet test, maybe the poor mans leakdown is not necessary?

And yeah, I'm not 100% sure that the carb is doing it's job correctly and may well be contributing to the problem. I've pulled it apart and cleaned it, made sure the jets were clear, etc, but it's certainly possibly that I haven't done that properly. Either way, that will get another strip down and possibly a rebuild kit.....

OR the other option i've been considering is replacing the stock Keihin PD carb with some upgraded/updated Carb tech (Like this Mikuni job) which kills two birds with one stone as the throttle cables on the old girl are not in the best shape (some fraying and dried out spots in there for sure) and this kit comes complete......

It DID fire twice when I tried starting it a few weeks ago, but only for a couple of seconds, and would not stay running.

So.......the plan is;

1. Remove the engine (may as well, makes everything easier to access and gives me an opportunity to fully clean and then spray the frame black, dissemble clean and re-grease suspension linkages, polish up alloy parts, paint forks black, clean up rims and spokes - holy shit, there's a bit to do isn't there!)

2. Take her top off and see what's underneath (hmmmm :0)

3. Based on what we see, have another look at the carb and make a call on New Fresh Mikuni or full rebuild kit on the stock Keihin.

First step though is to set up my workspace so it's cleaner and better organised for when the above happens.......no doubt there's MANY weekends of fun ahead with strip down and rebuild.....Will keep you posted and thanks again for your comments!
 

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I’m glad to see that you are making progress. If I were you, I would get it running with the carb, etc. that you already have. Ride it for a few miles. Put some load on the engine. Put it through its paces.
The fact that the wet compression test yielded a higher cylinder pressure tells you that ring seal was improved by adding the oil. However, that doesn’t mean that the rings are definitely shot. The cylinder walls could have been dry or the rings stuck. By getting the engine running and placing it under load, then doing a compression or leakdown test, you will be able to better assess it’s condition, before you start tearing it apart and spending money. Just my opinion.
 

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Discussion Starter #34
I’m glad to see that you are making progress. If I were you, I would get it running with the carb, etc. that you already have. Ride it for a few miles. Put some load on the engine. Put it through its paces.
The fact that the wet compression test yielded a higher cylinder pressure tells you that ring seal was improved by adding the oil. However, that doesn’t mean that the rings are definitely shot. The cylinder walls could have been dry or the rings stuck. By getting the engine running and placing it under load, then doing a compression or leakdown test, you will be able to better assess it’s condition, before you start tearing it apart and spending money. Just my opinion.
Thanks upperb, I appreciate the comment. I'd really love to do what you suggest, get it started and test while she's warm but my challenge is......... I can't get it running! (My right leg is starting to get 50% larger than my left, due to all that bloody kickstarter work! haha. It was hard to start the last time I rode it years ago, which is a total PITA)

The end goal of this project is to have a bike that starts easily, one or two kicks. So I might take the top end off and have a look....... can't hurt right? (Famous Last Words!) ;)

Thanks again.....(y)
 

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It shouldn’t hurt, but remember that the further you tear your bike apart, the more time, money and motivation it’s going take to get it back together and rideable. Think about this before you dive in deeper. I truly wish you the best.
 

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Discussion Starter #36
It shouldn’t hurt, but remember that the further you tear your bike apart, the more time, money and motivation it’s going take to get it back together and rideable. Think about this before you dive in deeper. I truly wish you the best.
Haha, yeah I fully agree that I could be getting myself into a hole that I'll need professional help digging my way out of.......hahaha.

But, nothing ventured, nothing gained right?

Part of this project's context was the benefit of learning, which is why I'm initially deciding NOT to send the bike to a mechanic and say, "...Here you go, here's AUD$1000+, do it for me....". I know I might end up spending more time and money if I bugger it up trying to do it myself, but at least I'll learn some stuff.

Maybe I should take the fact that I can't get it started right now as a bad omen and reflection of my shitty mechanical skills......BUT f&$k it, I'm gonna have a go and see where we end up.

Thanks for your wishes mate, keep your fingers crossed! :p:)
 

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Valve seats can be a source of compression leak same as piston rings, difference is where the pressure leaks to, rings leak and the pressure goes into the crankcase, valves leak and pressure goes out the exhaust port or back out through the intake. Your carburetor can not function if the intake vacuum pressure is not perfect (and in the right direction) so you really can't get the motor to work good and tune that carb until you fix the compression issues.
 

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Discussion Starter #38
Valve seats can be a source of compression leak same as piston rings, difference is where the pressure leaks to, rings leak and the pressure goes into the crankcase, valves leak and pressure goes out the exhaust port or back out through the intake. Your carburetor can not function if the intake vacuum pressure is not perfect (and in the right direction) so you really can't get the motor to work good and tune that carb until you fix the compression issues.
Thanks TrialsRider.....Just so I'm clear (and talking this out loud in my head)......you're saying that low compression generally can impact intake vacuum pressure? ie the leaky valves may be impacting the air fuel mixture entering the cylinder or worse causing Positive pressure when there should be a vacuum?

And therefore a top end strip and inspection is in fact the logical next step to a) sort out the compression loss and b) allow the carby to operate as intended?
 

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Correct, odds are against the intake valve or seat being a problem only because the exhaust valve and piston rings are more prone to extreme heat and wear but low compression is often accompanied by lowered intake pressures for the same reasons, poor sealing and leak by.

Internal combustion engine is very much like an air compressor or water pump, if it leaks performance suffers.
 

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Discussion Starter #40
Correct, odds are against the intake valve or seat being a problem only because the exhaust valve and piston rings are more prone to extreme heat and wear but low compression is often accompanied by lowered intake pressures for the same reasons, poor sealing and leak by.

Internal combustion engine is very much like an air compressor or water pump, if it leaks performance suffers.
Got it! Thanks TrialsRider! (y)

2 x New Pistons for Front brakes just arrived today, so I'll rebuild them & the master cylinder while I set up the workspace (and work up the courage) to take the engine apart. haha! ;)
 
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