Newbie - Urgent Help Req'd

[bmk]

Hi Baldini,

 

All I know of the previous work is what the last owner told me, which was that the engine and gearbox had had a repint and that there was some recall work done to the engine.

 

Other than that I don't know any more as to what was involved in carrying out the work.

[pete roper]

Interesting. I would suggest that the problem may not be down to the cap being on back to front alone, (Although this may of been a contributing factor.). The clearance between a split plain bearing like a big end and the journal it rotates on is essentially a manufacturing thing. The bearing clearance will either be too big or too small or within tollerance.

 

What causes a bearing to spin is too high oil pressure meaning that the internal friction between oil and bearing overcomes the friction betwixt the back of the bearing and the rod or the rod eye being too large for the bearings so that when they are tightened down there is insufficient friction betwixt shel and rod for the bearing to stay in place. (Sorry, gotta go and sort out a little family tiff, I'll continue this a bit later!).....

[bmk]

Hi Pete,

 

I can see where you're going with this, but having seen the damage, it's not the case here.

 

The bearing spun eventually because of wear, the bearing itself is extremely worn and has been hammered out of shape by the crank, allowing it to eventually spin.

 

As I said in an earlier post, the mains and rh cylinder journal are all totally unmarked and as you would expect.

 

As with all wear you will get to a point at which the clearances will suddenly accelerate and thus cause failure, which is what seems to have happened here.

[pete roper]

OK, but it's very difficult to tell if the problem is with an out of round or mis-sized rod after the damage has occured. Unless the shell and rod are still sufficiently undamaged to leave a decent witness mark on either you won't be able to tell if it was poor sizing, ovality or a bearing problem.

 

The point I was going to try and make is that it is imperative that if the rods are going to be re-used, with or without the caps aligned correctly, it is essential that they be re-sized and the nip should be ascertained with new shells and roundness of both installed bearings and the journal checked and double checked.

 

If a new crank and rods are being installed then I would STILL, as a matter of course check the nip, (Belive me people this IS the correct technical term!) and, if a decent internal and external micrometer wasn't available, plastiguage the bearings two or three times on the bench in different positions.

 

I would suggest that in this case failure is far more likely to have been due to a discrepancy in rod to bearing sizing rather than bearing to journal. If the same rods are re-used without the sizing being corrected then the same failure will occur again. I may well be preaching to the choir here but I've seen so many *rebuilds* done by people who seem not to remember the basics from their apprenticeships or conversely, because modern motors so rarely go tits-up they've never had to learn them, that I think it's worth making sure the job is done right.

 

If people need an explanation of the whys and hows of back clearance and the checking of nip I'll happily oblige but I don't want to shit people off by telling 'em stuff they already know.

 

Pete

[callison]

If people need an explanation of the whys and hows of back clearance and the checking of nip I'll happily oblige but I don't want to shit people off by telling 'em stuff they already know.

 

Pete

 

I think I would comprehend it better if you did explain Pete. You needn't do it now, but if you would post one of your famous Roper treatises on the subject in the Technical Topics section, I'm sure there are a lot of us that would really appreciate your efforts.

[pete roper]

Gladly mate, as long as people remember I'm just a spud-thick mechanic. My forte is explaining things in easily understood terms, I don't claim to be able to give chapter and verse engineering descriptions but I do hope that I can convey not only what is important but WHY. It's the WHY that is so often missing and causes most of the problems!

 

Incidentally, how many of your stable are up and running right now? Is the Sport going yet? I seem to remember that it was giving you a *shirtload* of grief a while back????

 

Pete

[pete roper]

OK, lets start this again. Hopefully I won't get side-tracked by my two sons trying to kill each other

 

Interesting. I would suggest that the problem may not be down to the cap being on back to front alone, (Although this may of been a contributing factor.). The clearance between a split plain bearing like a big end and the journal it rotates on is essentially a manufacturing thing. The bearing clearance will either be too big or too small or within tollerance.

 

What causes a bearing to spin is too high oil pressure meaning that the internal friction between oil and bearing overcomes the friction betwixt the  back of the bearing and the rod or the rod eye being too large for the bearings so that when they are tightened down there is insufficient friction betwixt shell and rod for the bearing to stay in place.

56684[/snapback]

 

Alternatively spun bearings can be caused by the oil pressure being too high due to a faulty relief valve or insufficient contact between the back of the shell and the rod itself.

 

Firstly lets consider why the bearings are a separate part from the rod at all. Well the real reason is simply that they are sacrificial. There is absolutely no reason why you couldn't just machine the steel of the rod to an exact fit with the pin and run it. The problem is that any contamination of the oil, particulate matter etc. would damage the pin and rod surface and once damaged you'd have to throw both away. By using a softish bearing material any particulate matter simply embeds itself into the bearing and the bearing will continue to function without damaging the journal it runs on. When it gets damaged beyond serviceable limits you can simply take it out and replace it with a new one rather than having to buy a new rod and crank, (In this case it's a rod and crank but any plain bearing is the same.)

 

OK, so what prevents the bearings simply spinning in the big end eye? I'll betcha that most people think it's the little tabs on the ends of the shells, right? Wrong! The little tabs are there basically to make sure that the bearing is centralised laterally in the eye of the rod. Yes, they will help a bit to prevent the bearing from spinning but what really keeps 'em still is friction between the *back* of the shell and the surface it sits on in the rod. this is the 'back clearance' and depending on how well the rod is machined and the bearing is manufactured it governs the ability of the bearing to resist spinning.

 

If you remove a rod from a motor and remove the shells you can see by looking at the back of the shell and the inside of the rod where it sits witness marks, (the metal will be a different colour.) which show how tightly the bearing has been pressing on the rod or cap and where oil has been able to seep in between the two. Obviously, since the idea is to prevent the bearing from spinning you DON'T want oil in there so the greater the area beneath the bearing that is a lighter, shiny colour, the better. Guzzi rods are usually pretty good in terms of the rod machining and back clearance.So how does one check this to ensure that the clearance is right before installation?

 

Well, quite simply you can't! What you can do is ensure that the big end is perfectly round, (Or as close to it as possible.) and that the bore of the rod is not tapered or damaged. Then you have to make sure that when the bolts are tightened up there will be adequate pressure exerted on the bearing halves to ensure that they are pressed tightly against this round and un-tapered surface in the bore. So how do you check that?

 

As mentioned before the actual clearance of the bearing is a result of it's manufacture and the size of the journal it runs on. The thing is that the shells are made fractionally larger than the ID of the rod eye. As the bolts are tightened the bearings won't deform enough to change the clearance betwixt bearing and journal but they DO compress against each other forcing the back of the shell into tight contact with the bore of the eye. This force will also try to push the cap away from the rod and it is this that allows you to find out whether there is going to be sufficient back clearance.

 

Take the rod and cap. Clean the surfaces of both where the bearing sits VERY, VERY carefully. I usually give 'em a spray with carby cleaner then wipe them obsessively with a soft, lint free, cloth. Repeat with the back of the shells and then install the shells into the rod and cap. It is VERY important that the face between the rod and cap and the shells be clinically clean as any foreign bodies left in there will deform the bearing, bugger-up the clearance and the ability of the oil film to wedge and shorten the life of the bearing. Once the shells are installed the cap should be placed on the rod, (The right way round!) and the bolts and/or nuts installed with their threads lubricated well with moly paste or some other anti-sieze product. The rod can now be placed in soft jaws in a vice with the jaws clamping the rod part of the big end eye from the side and the two bolts/nuts torqued down to their specified working torque. Once THAT is done you release just ONE of them. When you do this the cap will be forced away from the rod on that side by the pressure the shells are exerting between the two and a feeler guage can be used to measure the gap between rod and cap. This is called 'Measuring the nip' although some joyless bastard with no sense of history has over the last few decades started talking about 'Measuring the *Crush*'! He probably thought 'Nip' was to frivolous and tried to make it more serious. I hate these pompous arseholes!!!!!!

 

I can't offhand remember what the exact spec is but I'd say that for our size journals and bearings you'd be looking at 8 to 10 thou nip. Too much nip and it indicates the bearings are too big for the bore, (Or the bore is too small for the bearings!) and then the shells WILL deform and go out of round as the rods are installed on the crank. Too little nip and there will be insufficient pressure on the shells to ensure they won't spin in the bore in service. Reasons for this can be that the bore is too big or the bearings too small, ovality of the bore or damaged shells, any which way it won't work boy-o!!!!!

 

Once the rods are assembled on the crankpin, (With heaps of moly paste, I use Penrite camshaft and bearing assembley compound, lovely stuff and you can stick it in your bevelbox!) you can check if the clearance is correct pretty easily by simply pulling the rod up to the top of the crankcase mouth and letting it go. It should slowly drop to the bottom of the mouth, (speed will depend on ambient temperature and it's effect on the viscosity of the moly compound.) but it should be smooth and *slow*. If it just drops with a clank the clearance is too big for some reason, if it just sits there like a sodding great errection and you have to poke it to move it then either there is some contamination in the bearing or it's simply too tight for some reason! Yes, you can plastiguage it if you want but if you've measured the pin accurately, the bore of the beaings accurately and know the nip is right then that simple 'Look and Feel' test should be good enough. Works for our racer that last weekend was circulating at Oran park at the same speed and with identical lap times as a 2004 FZR 600 You want more precise? Go and buy a plant in Hamatsu!!!!!

 

Hope that helps. If the bearing had been hammered out of shape in this case the rods, if re-used should be resized and I'd get 'em crack tested too. I'd also double check the piston to head clearance known as the *squish*, (Another lovely old-fashioned term that probably the same joyless bastard has tried to get us to call the 'Quench"!) as insufficient squish clearance is in my experience the commonest cause of hammered out big ends, (Piston hits head at top of stroke, quite often this doesn't do it hard enough to make much noise but the big end shells disintegrate. Double check that the top ring isn't tight in it's groove too, that's a good give-away!)

 

Best of luck with it anyway. I hope that's satisfactory Carl? If anyone has any questions I'll do my best to answer them.

 

Pete

[bmk]

Hi Pete,

 

Good description, but the one thing you haven't really made clear in relation to this particular failure is that the big end cap was assembled onto the rod the wrong way round.

 

This is significant as the big end journal is machined into the rod with the cap in place and then marked. Assembling it incorrectly will then automatically lead to the factors you describe above as the hole in the big end is no longer round.

 

It may be only very slightly out of round but as you point out it only takes a little oil behind the bearing to start the process.

[pete roper]

Mate, I never said that the problem wasn't caused, (at least in part.) by the incorrectly fitted cap, simply that in a situation like this where a young engine has gone tits-up in a major way I'd be looking a lot deeper than just finding one problem and fixing that and then pronouncing it cured!

 

I currently have a Mk IV Lemans in my shop, it's a mates bike and I know how it has been cosseted all it's life. The thing is that it lost oil pressure and the deeper I've gone into it the odder it looks. I've found a couple of things that may well be the source of it's problems but I put the proposition to him that it would be better to go through it and zero time it. I said wait 24hours to think about it but he got staright back and said 'Go for it'. This to me is the wise decision because it means we can check *everything* rather than just fixing the superficial shit!

 

All I was suggesting was that you get whoever is doing the rebuild to go through everything with a fine tooth comb as it goes back together. I'd do this as a matter of course but if your dealer is NOT a commited Guzzi enthusiast then they amy just fling it back together having isolated *a* problem and not have really got to the bottom of it. all I was suggesting is care and caution, I wasn't suggesting the original diagnosis was wrong!!!!

 

Pete

[callison]

Incidentally, how many of your stable are up and running right now? Is the Sport going yet? I seem to remember that it was giving you a  *shirtload* of grief a while back????

 

Pete

 

The whole lot of them are in storage at the moment. After we move into the new house, I get to start on them. The Sport 1100i has never been resolved - but - a mutual friend of RacerX and I had similar problems with his Sport 1100i and apparently, replacing the stock cam chain tensioner with the Agostini type fixed his problem. I have the new tensioner awaiting installation. If that doesn't work, I have an entire V11 Sport wiring harness I can drop in and try a completely different type of computer! If that doesn't work, I have lots of hammers... Ah, no, couldn't do that, but the feeling tends to persist at times. I have replaced or substituted known good sensors for every EFI sensor on the bike, changed the regulator, the battery, tried Cliff's computer, used every explitive I know and still haven't gotten it working. The cam chain tensioner is just about the only thing left.

 

The V11 Sport awaits resolution as well. The first thing I'm going to do is remove my hokey relay/fuse installation that sits in front of the battery and move the individual components somewhere else. I strongly suspect that since the only time the fuse blows is when I sitting on the bike, that the front of the seat tab is moving back under acceleration and causing my weird wiring addition to ground out somewhere. Now, since that seems just a little weird, I'll just add that I added two relays to handle a heated vest and horns. I also wanted them to be able to actuate only when the bike was running. To do that, I tapped off of the bottom of the fuse block - on the ECU lead - to provide power to the two relays. So, when things go awry, that's the fuse that blows - with very negative repercussions. It ought to be a simple fix really, re-locating the parts and re-soldering the wire lengths to the new location will be the most difficult part. Then it should work. I hope. Then the fun begins. I have to get the beast registered in a new state and the VIN does not match the frame. I have the original, bent, twisted frame, so at least I can do something about it. I would have done it before I left California, but I couldn't trust the bike to make it down to the Department of Motor Vehicles, plus strapping the old frame to the back of the Sport didn't seem too realistic.

 

The California works fine. Too bad that immediately after I replaced the clutch plates, the clutch pushrod seal let go and oiled up the plates. I've degreased them, but there is still a small bit of plate shudder when the clutch is engaged. So be it. 4000 miles later, I haven't had any problems. That bike however, is slated to be replaced with a Breva 1100. I'm just not fond of the California, despite the pretty fair use I've gotten out of it.