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A very good point ~ you say you're running it at 5,000 ~ 6,000 RPM's, this is a lightweight bike and that's pretty fast for open highway speeds unless the sprockets have been changed to allow it to accelerate quicker .

This bike's comfortable cruising speed it 60 MPH +/- and it should do that at less than 4,000 RPM .
 

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Discussion Starter · #42 ·
today we opened the engine and found the main problem, exhaust valve broken, luckily the old owner gave me the same bike (as spare parts) and i have a head with the valves that seem alright, friday my friend brings the tool to remove the springs and the one to flare the valve seats and check.
The cylinder is not in a bad way, the piston rings have drawn some oil but there are no deep grooves, I would like to redo the whole new cylinder but before spending a lot of money I go to a mechanical workshop and see how it is with the right tools. put at the level of measurements and at best I only change the piston rings this time
 

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Discussion Starter · #43 ·
Here's a link to dynamic timing lights, I don't live in Ireland (altho I AM Scots/Irish) so I don't know how your local partshaus works.
Nate, today I understood what you meant, the flag is small on the forum page but I'm not Irish but Italian:giggle:
 

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Italian, shmalian ~ I'm in the U.S.A. but am of Scots/Irish extraction .....

I hope you got an inductive typ timing light, I see they now sell battery powered ones .

I buy tools used often, from pawn shops or wherever I can find them .

I'm amazed that thing started and ran with a valve like that .

This is most often caused by failure to check and adjust the valves .

You can and should hand lap the new valves before you install that used cylinder head .

Look closely at both cylinders, run your fingernails around the bore, if there's any tiny grooves like an old record, try the other cylinder .

At te very least, new piston rings, I'd replace the piston too as factory HONDA new ones are not terribly expensive .

Remember : there are a fe rubber O-Rings, do not attempt to re use them

VESRA makes very good low cost engine gasket kits that come with all the O-Rings and the copper sealing rings too .
 

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Discussion Starter · #45 ·
Italian, shmalian ~ I'm in the U.S.A. but am of Scots/Irish extraction .....

I hope you got an inductive typ timing light, I see they now sell battery powered ones .

I buy tools used often, from pawn shops or wherever I can find them .

I'm amazed that thing started and ran with a valve like that .

This is most often caused by failure to check and adjust the valves .

You can and should hand lap the new valves before you install that used cylinder head .

Look closely at both cylinders, run your fingernails around the bore, if there's any tiny grooves like an old record, try the other cylinder .

At te very least, new piston rings, I'd replace the piston too as factory HONDA new ones are not terribly expensive .

Remember : there are a fe rubber O-Rings, do not attempt to re use them

VESRA makes very good low cost engine gasket kits that come with all the O-Rings and the copper sealing rings too .
I will get one shortly to get things done right, think that in addition to starting and being regular the engine has never made strange noises ... that's why these engines have the reputation of being indestructible, certainly I will lapper the new valves and possibly I will redo the seat if it should be in bad shape. The hand cylinder liner does not feel any obvious sign, already perfectly cleaned to carry out the verification.
I try to find a complete original piston at this point, thanks for the advice

Luckily I live not far from ATHENA, a company famous all over the world for engine components and gaskets and I have already bought them
 

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O.K., well and good .

Don't touch the valve seat until you've tried to lap the new valve in, it's very easy to take too much off the seat .

Yes these are sturdy little engines capable of serious punishment .
 

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That little engine did pretty well to produce 75psi of compression with a chunk out of the intake valve.
 

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Discussion Starter · #48 ·
O.K., well and good .

Don't touch the valve seat until you've tried to lap the new valve in, it's very easy to take too much off the seat .

Yes these are sturdy little engines capable of serious punishment .
Thank you, I will be careful in touching the valve seat, tomorrow I will let you know, I am considering taking a piston increased by 0.25mm and polishing the barrel of the same size in the grinding workshop, since I have everything disassembled better do it
That little engine did pretty well to produce 75psi of compression with a chunk out of the intake valve.
and to run well at low speeds without making strange noises 😂
 

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Unless the cylinder bore shows wear I'd leave it alone ~ over size piston doesn't give much more power but does make the engine run hotter, not a good thing .

I'd replace the cam chain too, they're delicate and tend to stretch, this causes cam timing to be retarded, loosing that crisp throttle response .


Look closely at the rubber cam chain idler wheel too ~ they get stiff and hard with age, unless it's perfect you'll be way ahead replacing it too .
 

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Discussion Starter · #50 ·
Unless the cylinder bore shows wear I'd leave it alone ~ over size piston doesn't give much more power but does make the engine run hotter, not a good thing .

I'd replace the cam chain too, they're delicate and tend to stretch, this causes cam timing to be retarded, loosing that crisp throttle response .


Look closely at the rubber cam chain idler wheel too ~ they get stiff and hard with age, unless it's perfect you'll be way ahead replacing it too .
Thank you very much for the advice, obviously it was understood if the measurement is ok the cylinder bore, in addition to any signs (which does not have deep) I would like to check it is not ovalized, in case it is ok I take only the piston ring or complete new standard piston.
There are no reference measurements for the chain to see if it is stretched? I can't find anything in the manual ...

However, later the tools arrive and we see the valve seat situation
 

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Discussion Starter · #51 ·
We disassembled the valves and cleaned the seats with two different types of valve seat sand, without removing any material.
Before removing them and then we did a test that my friend said it did at work, that it was a mechanical car, the test consisted of simply inserting the compressor gun and seeing if the valves had leaks (by spraying water over the valves) , he told me that there should be no leaks, in both tests there was a minimum leak, however, surely the pressure of a compressor is more than what the suction motor creates, in your opinion it is normal for this type of engines or is it better to have the valve seat checked by a specialized mechanical workshop?
And always in your opinion, the base of the cylinder and the head should be rectified in all cases to remove the remaining gaskets and make the surfaces shiny or can it be done with very fine sandpaper or other similar methods?

thank you very much
 

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It's not the motor suction you need to worry about holding back it's the compression and the big explosion inside the cylinder that will test the valve and seat.
There is a test for contact between the valve and seat. It involves some blue powder stuff and basically you are leaving a stain on the valve and seat where they contact. Should be covered in a decent service manual, it is in mine.
 

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Prussian Blue

... I looked it up.

" Clean the intake and exhaust valves thoroughly to remove carbon deposits.
Apply a light coating of Prussian Blue to the valve seat.
Tap the valves and seats using a rubber hose or other hand lapping tool.
Remove the valve and inspect the valve seat face.
The valve seat contact should be within the specified width and even all around the circumference. "


and they show diagrams and specs of how it should look.
 

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Best way to see if a chain is stretched is to lay it along side a new length of chain.
... & I think he's right about the idler wheel and guides likely being plastic and getting trashed first.
 

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Discussion Starter · #55 ·
Prussian Blue

... I looked it up.

" Clean the intake and exhaust valves thoroughly to remove carbon deposits.
Apply a light coating of Prussian Blue to the valve seat.
Tap the valves and seats using a rubber hose or other hand lapping tool.
Remove the valve and inspect the valve seat face.
The valve seat contact should be within the specified width and even all around the circumference. "


and they show diagrams and specs of how it should look.
ok, now i understand and i found in the manual, i hadn't seen it before, thanks a lot for the explanation,
Font Rectangle Number Document Circle

Best way to see if a chain is stretched is to lay it along side a new length of chain.
... & I think he's right about the idler wheel and guides likely being plastic and getting trashed first.
Thanks for the advice, the guides don't seem to have become plastic but hard rubber, are they made of soft rubber when new?
 

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Discussion Starter · #56 ·
I can't find Prussian blue powder easily, I read about who used the oil one(diluted with motor oil) for this type of checks, do you think we can do the same?
 

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Discussion Starter · #59 ·
Thanks to all, I got an oil one on amazon italy that many mechanics in the reviews said that diluted with oil and use it for conical checks as in our case and arrives tomorrow, from other stores it was to wait too long for shipping
 

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Okay, to answer your questions :

The cam chain is easily checked by placing the alternator rotor on the "T" mark then looking to see if the cam alignment marks are to - gether ~ they won't be .

The cam chain idler wheel is made of hard rubber, as long as NO VISIBLE WEAR , no bumps / cracks/etc. you can re use it .

The valve testing is also simple : assemble the valves, springs and so on then pour some gasoline in the ports, there may not be a drop of fuel leaking past the closed valve into the combustion chanber .

Typically in D.I.Y. jobs you'll see the edge where the valve meets the seat, begin to get damp after a few moments .

Test each valve separately then dry well with a clean cloth or paper towel before testing the other one .

When I said "hand lap the valves" I meant ONLY use the fine lapping compound .

You don't need Machinist's Blue for the home job, gasoline (NOT WATER !) will instantly show if you're good to go or need more lapping .

The pistons will almost certainly have worn ring grooves (called lands) so even if there's no longitudinal scratches / grooves they should be replaced to ensure the job is done to make it last ~ no fun doing all this only to discover next July it smokes again and you can feel the lack of compression in the kick starter .

How you approach the job often depends on your financial situation ~ I'm a Journeyman Mechanic so I can do as much as I want, others have to con$ider the financial outlay .

One last thing : your engine , like all Gasoline engines, burns the fuel, it does not ever "explode" it ~ exploding fuel inside the engine is called detonation or ping and is ruinous to the engine .
 
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