Piston/valve interface LM2...

[guzzista]

Ok, valve timing/ cam  chain tension..... You did pop the timing cover and check for slackness in the chain? . The last 2 Tontis I dealt with with mileage approx 15k had very slack chains as found.( like Pete says: old motorbikes with no known service history...) In both cases after adjusting tension and/ or replaced tensioner with Valtek Unit thing were a lot better. Cheers

[Vasco DG]

Open up the timing chest and have a look what's in there.

[Dukedesmo]

You did pop the timing cover and check for slackness in the chain?

Nope, never even thought about it. Regretting it now though...   

[Dukedesmo]

Not sure what I'm looking for but this all looks pretty good to me?

[Triple Jim]

I'd turn the crankshaft back and forth a few times and verify that the cam shaft follows the movement without any visible backlash, but things do look OK in the photo.

[Dukedesmo]

Can't see any backlash and all the nuts seem tight, the tensioner flexes a little whilst turning but I suppose that's what it should do?

[Vasco DG]

Yup, that all looks peachy.

By the way if you're interested I have a single 83mm Gillardoni kit for a round fin LeMans. It came off a bike whose owner trashed one side by failing to install a circlip correctly and I couldn't get an 83mm kit so he went to 88mm both sides.

Pete

[Dukedesmo]

So, a bit stumped now. Don't know where to go.

I have had it suggested that unleaded fuel may have caused the valves to seize? I don't know if this is likely but unleaded has been the only option for many years in Europe and even longer in the US, anyone know of any issues?

As for replacing pistons I don't think I'm comfortable unless they're a matching pair, looks like 83mm are hard to get hold of new but plenty of 88mm kits around at not unreasonable prices.

Whatever I get, I want to be sure the cause is known/solved before fitting new parts...     

[Vasco DG]

It may have an X8 cam in or something. No way to know without either graphing it to taking it out for a look see.

No, it won't be fuel related but the heads are obviously going to need to come apart so K-lining the guides will be one of the things that will be obvious to do.

Pete

[Chuck in Indiana]

I have had it suggested that unleaded fuel may have caused the valves to seize?

That's not likely. I deal with this kind of stuff with aeroplanes. I've seen valve problems with 100 octane low lead (not really low) where unleaded is actually better for valve guides/stems.
When a valve sticks, it is normally from a loose guide rather than a tight one. I know, counter intuitive.. but a piece of carbon will wedge in there.

[Vasco DG]

I'd have to think both valves seizing at the sme instant is unlikely. I'm guessing it's got some sort of 'Hot' cam in it like an X8 and the valves were't  pocketed enough, either that of its a milder cam but the pistons are high dome and over-revving has caused the valves to float and kiss the piston.

Pete

[Dukedesmo]

I'd have to think both valves seizing at the sme instant is unlikely. I'm guessing it's got some sort of 'Hot' cam in it like an X8 and the valves were't  pocketed enough, either that of its a milder cam but the pistons are high dome and over-revving has caused the valves to float and kiss the piston.

Pete

Indeed it seem most improbable that both would seize on the same day and I don't think I ventured too high into the yellow, let alone the red, zone on the rev counter (although I was enjoying the ride).

But how prone are these engines for piston/valve interface due to over-revving? I find it hard to believe that the first minor over-rev could potentially cause such damage especially as these bikes were raced back in the day.

Whoever fitted the pistons and cam (if indeed the cam is upgraded) presumably did so for more performance and so would likely have used it as such without problem? So unless something was done wrong in the first place, and I find it hard to believe that the problem wouldn't manifest it's self for 25+ years, then something must have gone wrong on the day - maybe rider error?  but I don't think so. I would have thought a Le Mans could deal with a bigger numpty than me?

Weak valve springs? maybe but both exhausts together and only the exhausts? - OK maybe the exhausts are more likely to hit than the intakes? but still something doesn't add up to me.

Would be interesting to know what cam is in it - I assume to remove the cam I'd need to slip all 3 pulley assemblies off together with the chains? (or split the chains) if so is there anything I should look out for, or is there an easier way of identifying the cam? I assume the cam will have a part no. or other identification that would tell me what it is.

Sorry for all the questions but I have no prior Guzzi experience and am trying to learn - though I'd rather not have jumped straight in at the deep end as I seem to have done! 

[Vasco DG]

It's thirty five years old. See previous post. The timing chest has been entered before as the tensioner is an aftermarket type. Cam? If you want to pull it your next task is to read a manual or search the web. Alternatively graph the cam and find a graph of the original and compare.

Pete

[Dukedesmo]

Fair comment, youth is not on it's side - it's not the only one.   

I don't really want to remove the cam as I'm just making more work for probably little or no gain but I am curious to know if it is something different, might try measuring/graphing.

Thanks for all the advice. 

[Vasco DG]

From where you are now pulling the cam is an hour or so's work. Why not do it?

Pete

[Dukedesmo]

Not got a suitable castle socket at the moment, sure I could get or make one though. 
 

[Dukedesmo]

Do herself a favour, buy a new set of Gillardoni's. If you can't get the 83mm sets get the 88's and be done with it.

The 88mm Gilardoni kit looks like the most viable alternative at the moment, pricing doesn't seem too bad and as new 83mm pistons appear to be rarer than rocking-horse shit they probably aren't an option, and I really don't want to fit someone else's used (abused?) pistons.

I understand they are a bolt-on fit, not requiring the cases to be bored? and not particularly high-domed so maybe more clearance for the valves? I'd appreciate anything you can tell me about the 88mm setup, are they a reliable, quality product? given the extra 100cc or so I assume torque output is better? is there anything else I should consider?

I want to get the bike back right, in fact if I can make improvements it'll make things even better. Spending money to fix your bike never seems as bad if you can end up with an 'upgrade' in the process, every cloud/silver lining etc.   

[PeteS]

A Gilardoni kit might solve your piston problem but if the original problem was weak springs or not enough valve guide clearance you may still have a problem. I would pull the valves out and check guide/stem clearances and have your springs tested for tension. There are folks here who can tell you what the minimum spring rate should be.

Pete

[Antietam Classic Cycle]

I understand they are a bolt-on fit, not requiring the cases to be bored? and not particularly high-domed so maybe more clearance for the valves? I'd appreciate anything you can tell me about the 88mm setup, are they a reliable, quality product? given the extra 100cc or so I assume torque output is better? is there anything else I should consider?

It seems to depend on where you source the kits, whether the case needs to be bored or not. MG Cycle says yes, HMB Guzzi says no - theirs are machined to fit. All should have the correct dome.



http://www.hmb-guzzi.de/shop/Guzzi-Engine/Piston-Cylinder/Cylinder-Kit-88mm--Lm-1--LM-2.html

http://www.mgcycle.com/index.php?main_page=product_info&cPath=68_129&products_id=2138

Chances are they're heavier than the 83s, so it would be advisable to rebalance the crank to suit.

[Dukedesmo]

It seems to depend on where you source the kits, whether the case needs to be bored or not. MG Cycle says yes, HMB Guzzi says no - theirs are machined to fit. All should have the correct dome.

Chances are they're heavier than the 83s, so it would be advisable to rebalance the crank to suit.

I'd be looking at HMB as I've had excellent service from him before and the favourable Euro exchange rate means I get a better deal and, yes he says no reboring or no rebalancing either as the overall weight is the same?

[Dukedesmo]

I would pull the valves out and check guide/stem clearances and have your springs tested for tension.

I plan on investigating that and any other possible causes before a rebuild, so I'll be bothering you all for a while longer yet.     
 

[Chuck in Indiana]

I'd have to think both valves seizing at the sme instant is unlikely. I'm guessing it's got some sort of 'Hot' cam in it like an X8 and the valves were't  pocketed enough, either that of its a milder cam but the pistons are high dome and over-revving has caused the valves to float and kiss the piston.

Pete

Oops, didn't realize that both valves had hit. Almost has to be float, then..

[oldbike54]

Oops, didn't realize that both valves had hit. Almost has to be float, then..

 Yeah , I think what several are trying to tell the OP is that a 30 year old set of valve springs , and maybe some higher compression pistons have allowed this to happen at less than redline .

  Dusty

[Dukedesmo]

Yeah , I think what several are trying to tell the OP is that a 30 year old set of valve springs , and maybe some higher compression pistons have allowed this to happen at less than redline .

  Dusty

Good point taken. 

[Antietam Classic Cycle]

I'd be looking at HMB as I've had excellent service from him before and the favourable Euro exchange rate means I get a better deal and, yes he says no reboring or no rebalancing either as the overall weight is the same?

Didn't see that the first time - lighter pins so overall weight stays the same.