Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
I have seen identical hairline cracks ( exactly same position) on a Yamaha YZF750 that belonged to Steve Parish.
Rod eyes had gone oval, was there any small end wear on your SFC?
Conrod failures
- Thread starter sfcpiet
- Start date
Rod eyes had gone oval, was there any small end wear on your SFC?
CLEMTOG
Hero member
"contacted the edges of the piston pockets. I put this down to a machining error,"
Piet that error should have been detected at the build stage, by the use of plasticine to check clearances of the engine by turning it by hand and then dismantling, something I have done a lot of in the past (1960's/70's) and am currently re-learning again with a triple engine, the pistons touching the valves must send shock waves elswhere which is never good, never mind valve sealing (causing weak running and hotter pistons) stem bending (creating high friction) etc
as Colin Chapman once said, "if it breaks on the slowing down lap then it was as light as possible"
Piet that error should have been detected at the build stage, by the use of plasticine to check clearances of the engine by turning it by hand and then dismantling, something I have done a lot of in the past (1960's/70's) and am currently re-learning again with a triple engine, the pistons touching the valves must send shock waves elswhere which is never good, never mind valve sealing (causing weak running and hotter pistons) stem bending (creating high friction) etc
as Colin Chapman once said, "if it breaks on the slowing down lap then it was as light as possible"
With you there, Clem.
But, as I don't know by whom and under what premise this engine was originally built, all I could do was to remedy as best I could. Twisting conrods never occurred to me. As stated, I didn't have enough time to thoroughly investigate the root cause, I created enough clearance to avoid contact. I will inspect the intact piston closely when I find a spare second...
piet
But, as I don't know by whom and under what premise this engine was originally built, all I could do was to remedy as best I could. Twisting conrods never occurred to me. As stated, I didn't have enough time to thoroughly investigate the root cause, I created enough clearance to avoid contact. I will inspect the intact piston closely when I find a spare second...
piet
piranha-bro2
Hero member
- Location
- Melbourne
Std rods, Red?
yes standard rods, not on the rebuild though
not keen on using standard conrods anymore
Thomas aus LAU
Hero member
At that time we had opened the engine because of atypical noises.
The right piston pin lag had apparently seized briefly and turned in the connecting rod eye. The other connecting rod bearing was also too worn. Both connecting rods seemed to have become very warm at the head. The pistons themselves didn't look bad and the piston clearance was still ok.
Thomas aus LAU
piranha-bro2
Hero member
- Location
- Melbourne
IIRC my SFC rods (4 of them) all have bluish tinge on the small end. It's noticeable because of the highly polished surface. I thought it might have been heat treatment.
More likely temper colouring from the heat of the piston. Good indicator of how good or bad your combustion is/was.
piet
helicopterjim
Hero member
- Location
- near Lone Butte, BC, Canada
Andy J
Hero member
- Location
- Isle of Man
I get the hydraulic lock issue contributing to a potential rod failure, but as most Laverdas I have ridden have a tendency to miss gears, how much does the resulting over revving contribute to the chances of failure in the future?
I’ve only had two broken rods, one on a SFC1000, which was a road bike and didn’t have high mileage when I bought it. I did a few miles on the road, and one race meeting at Snetterton before it threw the r/h rod on the second lap of practice at the TT in 1989. This failure would have been in the over 6000 rev range and probably in top.
The other failure was my ex Alto Performance 750 Formula race bike and that blew on start up in the paddock So less than 4000 in neutral. Bearing failure was almost certainly a contributing factor so not necessarily a good example.
I also await lots of comments about incorrect gear linkage etc set-up/user error….
I’ve only had two broken rods, one on a SFC1000, which was a road bike and didn’t have high mileage when I bought it. I did a few miles on the road, and one race meeting at Snetterton before it threw the r/h rod on the second lap of practice at the TT in 1989. This failure would have been in the over 6000 rev range and probably in top.
The other failure was my ex Alto Performance 750 Formula race bike and that blew on start up in the paddock So less than 4000 in neutral. Bearing failure was almost certainly a contributing factor so not necessarily a good example.
I also await lots of comments about incorrect gear linkage etc set-up/user error….
There are so many potential reasons. Some very simple - maybe Giuseppi and Luigi didn't care too much about handling of the raw forgings (pre machining) and just threw them into boxes. If the design of the rod was a bit bordline, then a nick could create a stress raiser, leading to eventual failure years down the line.
Jo
Hero member
- Location
- Cologne, NRW Germany
A very interesting article - never heard of this phenomenon before.
However, it also creates kind of inner cinema in my head. As you know, I've been running my overhauled engine for a good year now (and I'm very happy with it). In hindsight, I occasionally thought about if it wouldn't have been better to spring for some alternative rods too.
Anyways, it's water under the bridge now, time will tell...
Cheers,
Jo
However, it also creates kind of inner cinema in my head. As you know, I've been running my overhauled engine for a good year now (and I'm very happy with it). In hindsight, I occasionally thought about if it wouldn't have been better to spring for some alternative rods too.
Anyways, it's water under the bridge now, time will tell...
Cheers,
Jo
Missed gear = likely bent valve, and rod?I get the hydraulic lock issue contributing to a potential rod failure, but as most Laverdas I have ridden have a tendency to miss gears, how much does the resulting over revving contribute to the chances of failure in the future?
I’ve only had two broken rods, one on a SFC1000, which was a road bike and didn’t have high mileage when I bought it. I did a few miles on the road, and one race meeting at Snetterton before it threw the r/h rod on the second lap of practice at the TT in 1989. This failure would have been in the over 6000 rev range and probably in top.
The other failure was my ex Alto Performance 750 Formula race bike and that blew on start up in the paddock So less than 4000 in neutral. Bearing failure was almost certainly a contributing factor so not necessarily a good example.
I also await lots of comments about incorrect gear linkage etc set-up/user error….
Paul
Zanes don't count Andy, completely different design and far removed from the original 500 rods. The 500 rods occasionally have their moments, but usually only after the big end has gone AWOL. Haven't yet seen a snapped Zane rod, just horribly mangled big ends with the associated battering of the head, valves and piston crown... "deaf, dumb and blind kid" from Quadrophenia/Pinball Wizard comes to mind.I get the hydraulic lock issue contributing to a potential rod failure, but as most Laverdas I have ridden have a tendency to miss gears, how much does the resulting over revving contribute to the chances of failure in the future?
I’ve only had two broken rods, one on a SFC1000, which was a road bike and didn’t have high mileage when I bought it. I did a few miles on the road, and one race meeting at Snetterton before it threw the r/h rod on the second lap of practice at the TT in 1989. This failure would have been in the over 6000 rev range and probably in top.
The other failure was my ex Alto Performance 750 Formula race bike and that blew on start up in the paddock So less than 4000 in neutral. Bearing failure was almost certainly a contributing factor so not necessarily a good example.
I also await lots of comments about incorrect gear linkage etc set-up/user error….
But the SFC1000 is an interesting case.
I don't think a missed gear would play havoc with the rods, with valves, certainly. I find lots of slightly bent valves, possibly results of missed gear changes along the way. Especially exhaust valves can glow red hot when marching on, it only takes a little knock to disrupt them. I also find a lot of non-concentric valve seats, these would also certainly cause valve distortion over a longer period.
piet
I opted for Arrow rods on my 3C rebuild.A very interesting article - never heard of this phenomenon before.
However, it also creates kind of inner cinema in my head. As you know, I've been running my overhauled engine for a good year now (and I'm very happy with it). In hindsight, I occasionally thought about if it wouldn't have been better to spring for some alternative rods too.
Anyways, it's water under the bridge now, time will tell...
Cheers,
Jo
I think that today more than ever, a Laverda restoration means a crank rebuild and new rods.
And a solid wallet.
Paul
Andy J
Hero member
- Location
- Isle of Man
Despite all my cack-handed gear changes I have (so far) seemingly avoided bending valves, although I have often cringed as I wait for the sound of valves hitting pistons.
I bent an exhaust valve once after the local Laverda Distributor rebuilt my head, this happened 600ks into a ride while I was running it in after the work. They insisted my missed gear changes, warn out bushes in the left side change system caused the bent gear, my fail apparently and charged me again to fix it, big money after spending a lot for the original head work. I also converted to a right side change and that helped the missed changes a lot. Years later I heard they were new to Stainless valves and didn't use enough clearance in the new guides. Missed gear overrevs are a fact of life, hard to completely avoid.