I took off the timing chain cover, to see if anything was broken or loose but all looks good to me; Also plenty of oil getting to the heads, followers etc. I have discovered that these pistons are not the standard kit but are high-compression with a slightly higher dome, still shouldn't hit the valves - I don't think they had until Saturday and they've been fitted for over 25yrs. Maybe unleaded fuel is a possibility but to do the damage so soon/quickly seems odd to me, I would have expected a gradual deterioration?
The timing chest looks fine & its already got the "Stuchi" improved tensioner on it. From the pic the timing is good as the marks line up. From my experience, and I'm not saying Al is wrong, just from what I know and have seen on the Guzzi forums. Running unleaded the valves gradually, recess in the guides leading to you starting to run out of adjustment at the bottom (i.e. large amounts of thread showing above the adjuster). It just seems strange that both valves would stick, too much of a coincidence, its not impossible but it does strike me as very odd. If the pistons are non standard and not a recognized type that could just be the problem right there. Was the head gasket a standard type, I'm thinking too thin head or base gasket might lead to a problem too. Usually when doing this sort of thing squish is measured to check but I'm getting out of my league with that. Also do you know if its a standard cam? Problem there is that you'll need a special tool to get the crank sprocket retaining nut off to remove the timing chain before you get to the cam. Usually these are all on supertight. I don't have that tool as I replaced the castle nut with a hex from a Daytona so I don't need it. Any id marks on the pistons to try and find out where they came from? Have you joined Guzitech or Wildgoose? These 2 forums are probably the best place to get info, WG can be a bit cleaky but you should always get some sort of answer, especially if its an odd problem.
Do the larger valve cut-outs in the pistons line up with the inlet valves? If not pistons in backwards.
Yes it looks good in there, tensioner appears to be tensioning and no noticeable wear on anything. Both valves sticking together just doesn't seem likely or even possible, regardless of any fuel/heat issues? Don't know if gaskets are standard thickness, need to find out what standard thickness is first? Also don't know what cam is in it, didn't really want to strip it down much further as I'm just making more work to reassemble and it looks to me like I need to remove all the pulleys with the chain to get the cam out for identification? Pistons are stamped 'Mondial Piston' with part no. '2705.2' and on the top it says 'Guzzi' then indicates which way is exhaust ('sca') also denoted with an 'A' and an 'N'. But, regardless of compression, dome height etc. they have been in the bike a very long time so should be OK? Of course bike's been standing and maybe not been given any revs for a long time? but I really don't think I over-revved it (honest occifer!) to any degree that would cause damage - you would think that any quality aftermarket HC pistons are designed with clearances specifically for high-RPM use anyway! Valve springs look good and there are 2 springs per valve but I've not removed them yet as I still don't have a spring compressor and trying to get them out without will likely end in tears. I'm on a couple of Guzzi forums and have got some good info but still no closer to finding out the why/how it happened? Unless it's just a case of over-enthusiastic right hand - but even if this is so, I can't be first numpty to have ridden a Guzzi hard, especially given it's (albeit pre-historic) sporting heritage. I'll be stripping the heads for a good clean and replace anything suspect - if there's anything specific for unleaded (new seats, guides etc.) then I'm happy to do that for all valves at the time. But it would be nice to know what the cause was before filling it full of expensive new parts and buggering it up again... And, yes the pistons were in the right way round.
IIRC the Le Mans II had higher comp pistons than the Mk1. The head gasket wasn't particularly thick when I stripped my engines and replaced them. Here's an alternative guess as to the cause....... It's known that running on unleaded will make the engine run hotter......so maybe as you were giving it a good hiding, the engine got so hot, the pistons expanded perhaps a fraction more and being high comp/higher crown, it was enough for them to hit the valves. Old Jock might be right about a higher lift cam......but equally, if the timing was out slightly........... And..........Figaro may be right about it standing for a long time........perhaps the valve springs are so old they have suffered either for being in the same position while standing and their strength has gone, or even crush has taken place. Crush can occur when a high lift cam is installed and standard valve springs aren't changed. And another thought......if the cam followers are badly pitted (mine were screwed in under 7000 miles) and as they turn (which is the effect of the cam wiping them) maybe there is enough pitting to cause the cam follower to sit 'lower' on the cam, then as it turns it sits 'higher'......that could possibly be enough to upset the rocker arm clearances. When the barrels are off, stick your finger into the cam follower holes and draw them out....
Got the followers out and they are perfect, no noticeable wear, will check the springs etc. One thing I have discovered with regards to the repair/replacement is that it seems no-one makes the 83mm pistons anymore. I can find used pistons, (Gutsibits have used Hi-Comps) but I'd rather fit new and maybe avoid the higher domes for obvious reasons although presumably this would give less power? One option that is available is Gilardoni make an 88mm drop-in kit (pistons & barrels) at a not too unreasonable price, these are lower domed pistons so give more clearance whilst the larger bore gives an extra 100cc which should more than make up for any lost power but without the need for more revs, this maybe a good and, hopefully, safer option?
Before you get the Gilardoni kit make sure you don't have to open up the top of the crankcase so the bottom of the barrels slip in properly.........and get the right diameter head gasket. You will probably have to up the main jet size as well.
I understand that the kit uses 'Le Mans spec' pistons to give a similar CR to the standard Le Mans plus, all else being equal, a larger bore should give a higher CR anyway by virtue of compressing more volume into the same space? So maybe similar to current or just a tad less? but I would hope that the extra 100cc would give more than the drop in CR takes away? especially in the low to mid ranges. I'm thinking chasing HP with revs my not be the best option on a 35yr old (agricultural) push-rod twin...
I agree with Steve over any possible loss of the 10.2:1 compression ratio.....hopefully the OP's comment regarding the big bore kit he is talking about means the ratio is still OK (or more, possibly)......... Just check the diameter of the bottom of the barrels where they fit into the crankcase. As for timing chain replacement, when I fiddled with mine the alloy gears were the only type available and they wore far too easily..........so when I went searching for something better, I was offered the secondhand triplex chain and sprockets by Bernies at Watford.........I honestly don't know if they were a one-off (bloody well made and no casting marks etc) or whether they were one of many...... ......and as they had only done 1000 miles or so, they were really quiet and effective modifying the auto tensioner so it could also be adjusted from the outside as well was useful, though.
From what I have gathered on various Guzzi forums (fora?) the Gilardoni 88mm kit is considered a good setup and given that 83mm are not easily available other than used (could be more 'used' than mine?) then I don't have a lot of options. Also I'm told the aftermarket tensioner setup I have is pretty good, certainly better than the OEM 'rubber block', plus there's no wear on anything in there so whilst gears are ultimately better, I'm not sure if it's worth the change especially as they can also be problematic (wear on the alloy gears etc.) and therefore not always a cure-all solution, plus consider that most Guzzis are running fine with chains even after high mileages so I'll probably stick with it. As for the heads, I've got the valves out now and there are no nasty surprises; the exhaust valves are bent but everything else appears to be OK, could obviously do with a decoke & clean but I've contacted a local(ish) cylinder head specialist with regards to regrinding/replacing the seats and guides to the new valves and with regards to unleaded fuel etc. (and because they're 35 years old) so I'll get that sorted soon. Still not got a definitive answer as to what the cause was, as I can't find anything obviously wrong with it other than it's an old machine with aftermarket pistons that are a tighter fit than the original design spec, fitted by an unknown mechanic many years ago, so it may just be down to operator (me) error? Repairs are down to me anyway... and I'll get it all back up & running soon.
Ahh the great timing gear debate. Unless steel I wouldn't go near them with a barge pole, the alloy shreds and then its a race to see what gives first the gears or the sludge trap in the crank. The exception that proves the rule are Agostini timing gears, many people swear by them, personally I still wouldn't touch them. I think your are spot Sir Desmo with your assessments. Gilardoni I believe made the original barrels for Guzzi. If you're getting a set and they are available grab them. Gilardoni do runs of these things so certain types are available at any one time and others not.
To update an old thread; Engine now rebuilt, new big-end shells, pistons, cylinders, exhaust valves, valve guides, seats re-ground & heads refurbished. Run-in for 500 miles, heads re-torqued and valve clearances re-set, carbs balanced etc. got just over 200psi compression on both cylinders and running smoothly and pulls strongly. The bigger bore has filled in the bottom end & midrange whilst still pulling well at higher revs, feels less peaky than before but I've not run to the redline yet. Also needed a bigger/better battery as the 30ah was struggling to turn it over even when fully charged! So I got a Motobatt 32ah that seems up to the job - only downside is it weighs over 10kg. but I'd rather a heavy bike that starts than a slightly lighter (but still heavy) bike that I need to push... Warming up before a ride;
Looking luvley & sounds amazing I love that sort of hollow thump its gives, very different from a Ducati but really nice. On the battery I run an 18Ah Odyssey on the LM 1000 and it provides more than enough grunt to do the job, mind its bloody heavy too 6.7 kg, next time going Lithium. Got a mate who runs a 545 its 13Ah and it still does fine and that bike has high comp pistons. I'm still building my 1100 sport but I won't post up pics, its your thread John
DD.........I recommend you don't take it to the red line yet after all the work done to the engine...... .....a Guzzi LeMans isn't properly run in until 10,000 miles......!
