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Laverda Forum => Ride and Race reports => Topic started by: gareth99 on September 08, 2019, 20:26

Title: Another Montjuic race engine in pieces
Post by: gareth99 on September 08, 2019, 20:26
At the Festival of 1000 bikes I managed half of the first session before the engine made bad noises and left me at the side of the track near Edwinas.

This might be the cause.


Thanks to Mark and Becky Hastings and Andy Jessop for providing sympathy and tutting noises in equal measure.
Title: Re: Another Montjuic race engine in pieces
Post by: Paul Marx on September 08, 2019, 21:28
That Edwina is one heck of a woman.

Paul
Title: Re: Another Montjuic race engine in pieces
Post by: chrisk on September 08, 2019, 21:56
 ;D If it was an Indian Royal Enfield, the big end would be within tolerance.
Title: Re: Another Montjuic race engine in pieces
Post by: Andy J on September 08, 2019, 22:40
It's just a mere scratch! If it was built like Michael Dunlop it will be racing again in a couple of days......and winning!
Title: Re: Another Montjuic race engine in pieces
Post by: Laverdalothar on September 09, 2019, 10:37
and someone claims the Zane bikes would be letting go the big ends to early...   :o

Sympathy to you, hope you can repair it and have fun again soon!!
Title: Re: Another Montjuic race engine in pieces
Post by: maurice turner on September 09, 2019, 11:16
Oh my  :( :( :( :( :(
Title: Re: Another Montjuic race engine in pieces
Post by: Dellortoman on September 10, 2019, 02:08
At least the rod stayed in one piece so it wouldn't have bashed holes in the crankcase. The cylinder bore might have a few dings in it though, and I don't reckon the valves would be looking too healthy either.
Title: Re: Another Montjuic race engine in pieces
Post by: motoddrob on September 10, 2019, 04:21
Positive side is that you can now fit Carrillos ;D
Title: Re: Another Montjuic race engine in pieces
Post by: Tippie on September 10, 2019, 07:40
Thatís a right bastard. Lucky it didnít let go, would have been brutal. What caused it?
A nice winter job for you now.
Title: Re: Another Montjuic race engine in pieces
Post by: Dellortoman on September 11, 2019, 02:14
What caused it?

Interesting question. I find it rather intriguing to analyse failures such as this. It's a bit like air crash investigation. Once the cause is identified, we may be able to figure out a way to stop it happening again.

I don't reckon a piston breakage would also lunch the big end, so I reckon the series of events went something like this:

1. Big end bearing cage broke up - possibly as a result of a roller seizing or breaking up, or just a fracture of the cage itself. Cages do fail by themselves occasionally.

2. With the bearing cage gone, the rollers can move out of place and all squish over to one side of the big end pin. As soon as that happens, the eye in the big end of the rod loses concentricity with the pin, which may allow the rollers to escape. In Gareth's vid it appears that there are no rollers at all between rod and pin. There must be sufficient space for them to get past the crank webs.

2. With the rollers missing, the rod and piston can travel a few mm (one roller diameter) further down the bore than they're supposed to, most likely bringing the piston skirt within clobbering range of the crank webs. 

3. The shock load of the piston hitting the crank musta been what tore the gudgeon out of the piston.

4. Then on the up-stroke. The flailing rod and gudgeon pin (now out of the gudgeon hole in the piston) could have been shoving up on some other part of the piston skirt, pushing the piston further up the bore than it's supposed to go and mashing the piston crown into the cylinder head. Once the piston can't go any further, then the rod would have been subjected to a massive compression load, which caused it to buckle - the 'S' bend it ended up with.

5. Even if Gareth has the quickest reflexes in the world, it would have done a few revolutions before he could react and shut the engine down. Then the inertia of the crank would keep it spinning for a few more revs after he's hit the kill switch. So even if the piston stayed at the top of the bore, the rod would have been bashing up and down the cylinder maybe a couple of dozen times before the whole sorry mess came top a stop, further munching the piston skirt.

So, in my estimation, it was all down to a failure of the big end bearing. To determine whether it started with a roller failure or cage failure, gather up all the rollers from the sump (they should all be there) and inspect them. If there's a busted one, that's probably the culprit.

The ultimate cause could have been simple wear on the big end, or possibly poor lubrication. Perhaps a re-think of engine oil choice would be a good idea. May also be worth checking that the oil pump is operating properly and all oil galleries are un-blocked.
Title: Re: Another Montjuic race engine in pieces
Post by: sfcpiet on September 11, 2019, 09:11
That certainly did not happen over the course of only one weekend, the root cause must have been lurking for quite some time.

piet
Title: Re: Another Montjuic race engine in pieces
Post by: gareth99 on September 30, 2019, 18:32
Yea, lots to go at over the winter.

I was really curious how the bearing could let go so badly yet the con rod stay intact. At the time of the "event" it was revving about 8500-9000 in top gear and pulling well - no unusual vibes or noises until the big bang which was like a chain letting go.

I've been on holiday for most of September so now we will start the forensic investigation. I'll keep you informed !!
Title: Re: Another Montjuic race engine in pieces
Post by: Andy J on October 12, 2019, 18:46
I now offer further commiserations as I have just experienced a similar Ďincident Ď with my Zane 750 race bike. It didnít get much beyond start up for the first qualifying session this morning at Anglesey International race circuit. R/h rod let go, looks like the main baring failed. Hopefully most of the rest of the engine has survived, but still a shit end to the season.  :(
However I suppose it could have been worse and gone out on the circuit.
Roll on next year and hopefully all the bad luck from this year will mean a cracking good 2020.
Title: Re: Another Montjuic race engine in pieces
Post by: KERMIT1200 on October 12, 2019, 18:51
'Looks like it'    IT IS!!!!!!!!!!!!!!!!!!!!!! Its DEAD If the hole was slightly bigger I could have pulled the conrod out.

From the amount of white smoke that came up from the bottom of the engine and filled the gazebo I thought the 'Pope' was sending a message!!!!!!!!!!!!!!!!

Andy
Title: Re: Another Montjuic race engine in pieces
Post by: Rob on October 12, 2019, 23:13
Sheesh - sorry to hear that news, Andy. Bummer  :(
Title: Re: Another Montjuic race engine in pieces
Post by: Andy J on October 13, 2019, 13:05
And it's not as though I need extra work this winter.....
Title: Re: Another Montjuic race engine in pieces
Post by: Piranha Brother 2 on October 14, 2019, 00:05
Shaeza! That's a serious piece of misadventure there Andy. What a bummer.