Scooterotica

My Monza 225 engine has done around 3000 miles and for quite a while there has been a rattle coming from the top end that increases with revs. So today I have stripped the top end down to see if it was piston slap or small end failure and these are the results.

Piston rings – measured gap around 0.7mm, so looks like these need replacing.

Piston/cylinder clearance
When measured at cylinder head end, clearance was 0.008 inch, but I think that this is the wrong place to measure.


So measured at the spigot end and was 0.003 inch. Is this the correct place to measure and at 0.003, seems OK when checking with published data?


Piston score – This was done in the first 100 miles when the carb kept dropping off with that stupid solid rubber hose that came with the kit. But should I be concerned with these marks. Not much to be seen in the clean barrel.


Small end and gudgeon pin look OK, with no sign of sloppiness before I removed piston. So looks like small end bearing is OK. However, both the conrod and bearing is 20mm wide, but the slot for the piston is 25mm and therefore, the piston can slide left to right on the gudgeon pin by up to 5mm. Is this kind of gap normal? Note, the crank is a race crank that came with the CamLam kit
Does anyone recognise these reed petals. I think they are the originals ones that came with the kit, but Chiselspeed, at a later date, did fit a LTH 102215 30mm CNC Inlet manifold to give more panel clearance. I say this as I would like to replace the petals to see if it cures sudden rich four stroking up to half revs.


It would be great if anyone could comment on any of the above to see if I have missed anything or to confirm that I am on the right track. If so, I’ll contact CamLam for the replacement parts, which just looks like, petals, rings and gaskets.


And then get Dan to re-dyno

the last picture of the gudgeon pin- looks like its worn at either end and possibly other places. Got to admit that all the used pins I've seen over the years in a variety of engines have appeared perfectly smooth with no marks whatsoever.

Also, the small end bearing appears "blue" in places- is this a trick of the camera or overheating?

Just a couple of thoughts

Chris

I wouldn't worry about the marks on the piston, especially if they happened 2900 miles ago.

On alloy kits Ive always replaced the rings at 3 - 5000 mile intervals as the chrome on them does wear about then and its worth that to save the nicasil, it's all down to the type of riding though and the kit. yours being a reed valve I'd say that they're about due.

I personally think the gudgoen pins fine but I would be replacing the small end bearing and circlips as routine for the sake of a few quid.

As for the gap 'twixt piston and gudgeon pin side to side? You do know the barrel wont allow it to do that dont you?

PS can't comment on the reeds as I've never owned one or had enough experience Im afraid but there's loadsa lads here that'll know.

13 roller small end bearing?

I ran a monza for 3 or 4 years. Piston is ok. Get new rings, you can get harder wearing rings from cam lam.
That looks like a super monza piston (supplied with later versions of the kit) so get a 22mm wide small end to take up the slop. Available from same place.
Also 2 stage reeds are available that fit straight on. Also from Cam lam.
It will always run a little rich in mid range until you hit the power band as they need a large atomiser/needle combo for cruising at half throttle when you roll off from full. A correctly set up power jet can help with this.
Could rattle be head cowling? The heads that are used on newer muggys and monzas are quite beefy and fins can vibrate on the cowling sometimes.

p.s they are original reeds by the look of it and where is your timing set?

I ran the 20mm small end bearing that came with the mec crank on my monza with the same piston, when I striped mine down there was major wear and pitting on the pin like it got way too hot..I have since changed to a Yamaha 110 con rod and now use 22mm small end bearing YAMAHA part no. 93310-216E1

14 is a nice number

Hi Donnie

As for the gap 'twixt piston and gudgeon pin side to side? You do know the barrel wont allow it to do that dont you?

. Yes, I know what you mean. I know the barrel would not allow this, but I did wonder if the bearing, being 5mm less in width, could slide out of the conrod!!!!!.

Nelson
Thanks for the input and I have noted your comments. I will replace the rings, clips, gaskets and bearings, but from what I have discovered, it may well be a rattling cowl on the fins. Anyway, at least i have eliminated all other possible scary causes.

As for timing, I did set TDC and strobe to 18 degrees static, right from the very start and no real issues, in fact a great engine. But then it suddenely began to run boggy/rich upto half throttle, which was exhausted on an earlier thread. But although I have just replaced a failing stator and CDI unit, it is still massively boggy up to half throttle. So I am left wondering if the reed petals are slightly defective, although they look OK.

Just for completeness, it is a 30PHBH carb with powerjet and now that the stator and CDI are running correct, I have put back in the AV266 and X2 needle, as originally supplied by CamLam and dynoed by Dan back in 2010. So will probably replace reeds and mess around with the X2 needle.


As for Muppet, 42 was a good number, used to constantly doodle that number, but as I approached 42, I thought it might have some ominous meaning, like death, but clearly i survived that, but its hot down here.

paulnobodyimportant wrote: But then it suddenely began to run boggy/rich upto half throttle ...... it is a 30PHBH carb with powerjet .....

I'm sure you've already checked and this has been covered, but if not, check the powerjet adjuster isn't/hasn't moved through vibration? This was happening to another member on here, who ended up using a small piece of hose to keep it in place.

I believe the powerjet kicks in between half and full throttle, but still worth checking.

Cheers