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I think I killed it! Help!

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lonie
Trackday Trickster



Joined: 13 Aug 2009
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PostPosted: 09:44 - 20 Feb 2018    Post subject: I think I killed it! Help! Reply with quote

Hi all, having some trouble with my bike, so I was riding along and pulled out of a junction rather agressively when changing from 2nd to third the gearbox slipped back down to second (this is a existing problem I already knew about) causing the engine to potentially over rev.
The problem is now the bike won't rev past 4-5k and sounds very boggy it also sounds very "tappy" from the cylinder head. I'm fairly handy with a spanner and am willing to do the work bitno unsure as to what needs doing to fix the issue. A friend of mine told me it could have blowblown the valve Clearances out of whack does this sound about right?

Bike is a Chinese thing (I know they suck but it's all I can afford atm) the engine is a k157fmi ohc.

Could any of you point me in the right direction? I hope this is fixable as it is my only mode of transport. Engine seems to idle fine and run fine up to 4-5k rpm other than sounding like a bag of bolts so to me that indicates that it's not done any major damage but I'm no mechanic.

Thanks for the help[/code]
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MCN
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PostPosted: 09:54 - 20 Feb 2018    Post subject: Reply with quote

No idea what the engine is like.
Overspeeding a push rod engine can bend a push rod.
It can have a catastrophic effect and the rod drops out of position and gets mashed into places it should not be.
Or if fortunate, it stays in position but just cannot open the valve properly. The bend shortens the length.
The shorter length means a bigger clearance too which will make the engine sound more rattle and clatter.

Possibly only needs a new push rod.
If you cannot find a new rod you can 'sometimes' get away with bending the rod straight again. But that is a very risky repair as push rods are super-straight so the do not bend.

You can access the push rods by removing the valve cover and then the rocker arm shaft.
And FFS do not drop any bits inside the engine.
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lonie
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Joined: 13 Aug 2009
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PostPosted: 10:05 - 20 Feb 2018    Post subject: Reply with quote

MCN wrote:
No idea what the engine is like.
Overspeeding a push rod engine can bend a push rod.
It can have a catastrophic effect and the rod drops out of position and gets mashed into places it should not be.
Or if fortunate, it stays in position but just cannot open the valve properly. The bend shortens the length.
The shorter length means a bigger clearance too which will make the engine sound more rattle and clatter.

Possibly only needs a new push rod.
If you cannot find a new rod you can 'sometimes' get away with bending the rod straight again. But that is a very risky repair as push rods are super-straight so the do not bend.

You can access the push rods by removing the valve cover and then the rocker arm shaft.
And FFS do not drop any bits inside the engine.


Hmm okay thanks I will remove the valve cover and rocker arm and see if I can get them out hopefully it's just a bend and is fixable can't really afford a new bike Laughing
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Rogerborg
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PostPosted: 11:21 - 20 Feb 2018    Post subject: Reply with quote

MCN wrote:
Overspeeding a push rod engine can bend a push rod

Where are the pushrods in an OHC engine, you fvcking piece of Tef? They do these "156/157FMI" lumps in both OHV and OHC variants.

Although you are going to have to fire in there and see what's what. I'd suggest checking for a vent valve, or a failed cam chain tensioner.

Or a bent pushrod if it's actually an OHV, but don't tell us the bike, that would take the fun out of it.
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lonie
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PostPosted: 11:35 - 20 Feb 2018    Post subject: Reply with quote

Rogerborg wrote:
MCN wrote:
Overspeeding a push rod engine can bend a push rod

Where are the pushrods in an OHC engine, you fvcking piece of Tef? They do these "156/157FMI" lumps in both OHV and OHC variants.

Although you are going to have to fire in there and see what's what. I'd suggest checking for a vent valve, or a failed cam chain tensioner.

Or a bent pushrod if it's actually an OHV, but don't tell us the bike, that would take the fun out of it.


Engine is deffinatly ohc. So that means no push rods? Okay so I need to be checking valves and cam chain then?

Thanks
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stinkwheel
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PostPosted: 11:46 - 20 Feb 2018    Post subject: Reply with quote

I've seen tappet adjusters undo themselves too, if it has screw type adjusters.

I've also seen over-revved small CC bikes spin up their flywheel which would make the ignition timing out.
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Polarbear
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PostPosted: 12:25 - 20 Feb 2018    Post subject: Reply with quote

Rogerborg wrote:
MCN wrote:
Overspeeding a push rod engine can bend a push rod

Where are the pushrods in an OHC engine, you fvcking piece of Tef? They do these "156/157FMI" lumps in both OHV and OHC variants.

Although you are going to have to fire in there and see what's what. I'd suggest checking for a vent valve, or a failed cam chain tensioner.

Or a bent pushrod if it's actually an OHV, but don't tell us the bike, that would take the fun out of it.


but don't tell us the bike, that would take the fun out of it

Just incase you missed Rogers subtle hint. Wink
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lonie
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PostPosted: 13:13 - 20 Feb 2018    Post subject: Reply with quote

Bike is a sinnis vista 125cc.
Sorry didn't think that was relevant as I had posted the engine model my bad haha

Thanks
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MCN
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PostPosted: 13:25 - 20 Feb 2018    Post subject: Reply with quote

Rogerborg wrote:
MCN wrote:
Overspeeding a push rod engine can bend a push rod

Where are the pushrods in an OHC engine, you fvcking piece of Tef? They do these "156/157FMI" lumps in both OHV and OHC variants.

Although you are going to have to fire in there and see what's what. I'd suggest checking for a vent valve, or a failed cam chain tensioner.

Or a bent pushrod if it's actually an OHV, but don't tell us the bike, that would take the fun out of it.


I said, 'I have no idea what the engine is like".

You fucking piece of Bodyform (formerly Bodytard (soon to be Body of Evidence.)).
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weasley
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PostPosted: 13:55 - 20 Feb 2018    Post subject: Reply with quote

Rogerborg wrote:
They do these "156/157FMI" lumps in both OHV and OHC variants.


You Teffing piece of fuck. OHV and OHC are not mutually exclusive. OHV is a description of an engine that is not side-valved (flathead). Pretty much any and every bike engine out there since forever has been OHV. Some have also been OHC, whilst others used an in-block cam and pushrods. Yes, people have been using OHV ≠ OHC for a long time, but people are often wrong - sadly if enough people say the wrong thing, it becomes de facto right (evidence: "the proof is in the pudding", "money is the root of all evil" and so on).

I'd be amazed if a bent valve in a 2-valve, single-cylinder engine would allow it to keep running up to 4-5,000 rpm. Pulling the valve cover off may reveal the answer, or may not. A compression check will tell you if the engine is huffing and puffing as it should. This procedure is essentially non-invasive, unlikely to introduce further issues and could rule out the need to pull the head off (which, being a OHC type, means a bit of faff).
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Rogerborg
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PostPosted: 13:56 - 20 Feb 2018    Post subject: Reply with quote

lonie wrote:
Sorry didn't think that was relevant as I had posted the engine model my bad haha

It's a generic code that just means:

1 - cylinder
57 - bore (although it's likely to be 56.5mm so 56 and 57 engines are indistinguishable)
F natural air-cooled
M - motorcycle
I - displacement (125cc)

The k at the front has no well defined meaning.
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WD Forte
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PostPosted: 04:19 - 24 Feb 2018    Post subject: Reply with quote

hopefully you have an easy fix problem but
we had a Kymco Pulsar ( 125 OHC)of low miles which had a slipped cam chain and bent exhaust valve and wouldn't run.
Easy and cheap to check and fix if it is that
BTW
I found the cam chain adjuster to be rather flimsy so
would recommend care is take to see it's functioning properly and The timing marks line up
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bikenut
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PostPosted: 13:05 - 24 Feb 2018    Post subject: bike Reply with quote

Hi all, having some trouble with my bike, so I was riding along and pulled out of a junction rather agressively when changing from 2nd to third the gearbox slipped back down to second (this is a existing problem I already knew about) causing the engine to potentially over rev. :D

So either fix this engine gear problem and the "over rev" damage, or get an other engine, a good one.

When you have the good engine fitted, ( I suspect a gaggle of new threads to come from this like "How do I fix sheared off exhaust studs etc etc etc " ) take the buggered engine apart and assess, is it viable to repair as a spare engine ?

You have a manual and know of cmsnl, which could help.

You know of the special tools you could do with to take this engine apart and re assemble well. A good learning curve that will stand you in good stead.

You have said that you know how to use a spanner and are willing.

Have you had this bike from new or did it come "pre buggered " ?
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lonie
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PostPosted: 13:41 - 24 Feb 2018    Post subject: Reply with quote

Hi all, issues are now solved. I whipped of the valve cover and low and behold sat inside was one of the valve adjusters is had managed to vibrate loose and must have popped out when the engine over reved.

Put it back in place and adjusted the gap correctly and she is back to her usual if not slightly quirky self

Thanks for all then help
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stinkwheel
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PostPosted: 14:03 - 24 Feb 2018    Post subject: Reply with quote

stinkwheel wrote:
I've seen tappet adjusters undo themselves too, if it has screw type adjusters.


lonie wrote:
I whipped of the valve cover and low and behold sat inside was one of the valve adjusters is had managed to vibrate loose and must have popped out when the engine over reved.

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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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