Help Geoff

[ducatilover]

As anyone following my other threads has noticed, I have little tappy hammer gnomes in the GN top end.
The tap: A metallic tap, louder than you'd expect from wide valve clearances
Tap seems less prominent under load, get off the gas and it tapitytatiptgzzzzzzzzzztaptap (you know...)
The engine GN250, new .5mm piston/gaskt
New oil pump
New can
New cam chain
New tensioner
New tensioner/chain guides
Valves set to Suzuki spec
Ported GN250 head
GN250 rockers in great condition
As above for the rocker arms
Valve springs measure within spec
Don't seem to be bent :innocent:
200psi compression warm
No leaks at the headers
Valves lapped in.
Cam chain isn't loose, it only rattles if you back the tensioner out



My only theory is I have valve on seat noise, lots of it.
The seats aren't dropping and they look to be in great condition, no signs of erosion.
I am stumped, I offer beverages, hugs, scones to whomever can help out

[SS90]

As anyone following my other threads has noticed, I have little tappy hammer gnomes in the GN top end.
The tap: A metallic tap, louder than you'd expect from wide valve clearances
Tap seems less prominent under load, get off the gas and it tapitytatiptgzzzzzzzzzztaptap (you know...)
The engine GN250, new .5mm piston/gaskt
New oil pump
New can
New cam chain
New tensioner
New tensioner/chain guides
Valves set to Suzuki spec
Ported GN250 head
GN250 rockers in great condition
As above for the rocker arms
Valve springs measure within spec
Don't seem to be bent :innocent:
200psi compression warm
No leaks at the headers
Valves lapped in.
Cam chain isn't loose, it only rattles if you back the tensioner out



My only theory is I have valve on seat noise, lots of it.
The seats aren't dropping and they look to be in great condition, no signs of erosion.
I am stumped, I offer beverages, hugs, scones to whomever can help out

Hmm, neigh on impossible to diagnose from here, but as an apprentice I have rebuilt my fair share of Gmobiles.

Normally, (don't take offence) many people overlook the cam and rocker wear in Gns as source of rattles, and, more often than not, this is the cause, they only hold a liter of oil, and the top end is usually the first to suffer when the oil level gets low., I have seen cams that look to the inexperienced eye "as good as", but in actual fact they are worn to a point.

Comparing yours to a new one (if at all possible) is a quick reference.

Another one that springs to mind is , have the rockers been removed from the cam cover? They are held in place with 2 pins, that are simply pulled out (with some effort), and the rockers held central with 2 wave washers.

I saw one engine that has been rebuilt that these wave washers where omitted, leading to a rattling on overrun.

I would suspect cam and or rocker wear to be the culprit, as, like I said, sometimes they "look" OK.

New cams for Gmobiles are cheap as (although suzuki are known for less than sexy prices).

Look around the internerd, they are made in China, so parts are 72 hours away.

That said, support you local dealer, or they will find something else to do!

[ducatilover]

Hmm, neigh on impossible to diagnose from here, but as an apprentice I have rebuilt my fair share of Gmobiles.

Normally, (don't take offence) many people overlook the cam and rocker wear in Gns as source of rattles, and, more often than not, this is the cause, they only hold a liter of oil, and the top end is usually the first to suffer when the oil level gets low., I have seen cams that look to the inexperienced eye "as good as", but in actual fact they are worn to a point.

Comparing yours to a new one (if at all possible) is a quick reference.

Another one that springs to mind is , have the rockers been removed from the cam cover? They are held in place with 2 pins, that are simply pulled out (with some effort), and the rockers held central with 2 wave washers.

I saw one engine that has been rebuilt that these wave washers where omitted, leading to a rattling on overrun.

I would suspect cam and or rocker wear to be the culprit, as, like I said, sometimes they "look" OK.

New cams for Gmobiles are cheap as (although suzuki are known for less than sexy prices).

Look around the internerd, they are made in China, so parts are 72 hours away.

That said, support you local dealer, or they will find something else to do!

Brand new cam, journals are fine. (FWIW, they're $17USD from the bunch who make them for Suzuki)
Also have a re-ground DR250 cam
Rockers are new, those wave washers are in as-per owners manual
It is entirely possible that those washers are on the wrong side of the shaft (I've done the rockers twice, both times with the washers on the same side)


Got the shits after riding it today and got ready to split it and re-bearing it, but found that the cam locating bearing/thing (you know the wee half circle thing) was cruising around between the RHS rear head bolt and tensioner arm.
I must have done a whoopsie putting the head on yesterday, because there's no way it can come out with the valve cover on
But, bad noise was present before that...

I'll update again tomorrow
Just found that the very end of the thread on the crank (pulling flywheel to check starter clutch) is poo-poo, so I have to clean that up before I lose the plot and strip the cunt on there. :facepalm:


No wonder I was at a psychologist appointment today, I'm losing my engine building skills!

[ducatilover]

Seeing as the noise was there prior to the last head off job, I'll split the cases today and give the whole lot a good going over
Still trying to find a DR350 crank, LT500 crank would be the bizz (411cc on my 78mm piston) if it'd fit...
Otherwise I could look in to having an offset pin machined up? :innocent:

[Fast Eddie]

good luck, in these situations i thrash it til it blows up and then start with a...err...clean slate..sort of

[Subike]

all new, ok, and using all sorts of parts, so....
silly thought but
is one of the rocker adjusting bolts, just touching the rocker box after you assemble it?
or a similar item just touching somewhere in the crankcase, but only does so once fired up?
When assembling all the clearances are OK I presume, but under load that final .000mm of movement is enough to make the sound?

have you tried using a long screw driver as a stethoscope to listen to where the tapping is coming from if you can hear it at idle?

Been enjoying reading this voyage of discovery, experimentation and modification for the enjoyment of doing it.

[Madness]

Is it insured? Do you live near the ocean?

[ducatilover]

good luck, in these situations i thrash it til it blows up and then start with a...err...clean slate..sort of
Done bro :D blew a bearing and punched a valve

all new, ok, and using all sorts of parts, so....
silly thought but
is one of the rocker adjusting bolts, just touching the rocker box after you assemble it?
or a similar item just touching somewhere in the crankcase, but only does so once fired up?
When assembling all the clearances are OK I presume, but under load that final .000mm of movement is enough to make the sound?

have you tried using a long screw driver as a stethoscope to listen to where the tapping is coming from if you can hear it at idle?

Been enjoying reading this voyage of discovery, experimentation and modification for the enjoyment of doing it.
Found it, it was running the crank bearings, one of which randomly seized, and because the .5mm o/s piston had a higher compression height, crank float = goodbye valve.
I'm bloody chuffed I found the problem though :yes:


Is it insured? Do you live near the ocean?

No to both, but, I live right next to a river and very large bank. Might insure it today and throw it down there tomorrow, but please don't tell

[Madness]

Might insure it today and throw it down there tomorrow, but please don't tell

I promise bro. We're tight :niceone:

[ducatilover]

I promise bro. We're tight :niceone:

Thanks, I'll post it to you on bookface, that way it'll be legitimate and I would have definitely done it