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Head gasket........

17K views 24 replies 9 participants last post by  DukeDesmo 
#1 ·
Was out for a ride today, bike running fine but when I got home I see this;



Not looking good, I assume it is the head gasket that's leaking as the coolant appears to run down from there (doubt it's running up from cylinder base gasket). I can't see it leaking when I run it so presumably it only does it under pressure/heat and the coolant level doesn't seem to have dropped so it's not run dry or anything.

So I'm guessing just the gasket so I need to replace that, never had the heads off before so don't have any special tools that I would need (to get at head bolts) so probably going to be a shop job, any idea what sort of labour is involved, also parts needed. If it was winter time I'd be tempted to strip down further for some 'preventative maintenance' (or maybe some blueprinting etc) but for now I just want to get back to being able to ride.

Oh and whilst I was looking I found a fuel leak, looks like the fuel hose is leaking at from the crimped end at front of the (rear) cylinder - two problems for the price of one! but at least I can fix this one easily though, I suppose 10 year old fuel hoses owe me nothing. :(

Back to the gasket, If I do the job myself, I presume I can get the head off without removing the engine?
 

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#3 ·
I'm a bit skeptical on it being JUST a bad head gasket. I've used pretty shitty-ass gaskets before and done multiple track days before without any leaking. If you've truly got a gasket leak, it could be a much more serious problem and I highly doubt the bike would run properly if at all. This is why I'm thinking its something else.

I'd start by pulling the tank, airbox and breather box off, and really carefully following the "line of destruction" from the top (I see dots on the valve cover) all the way down to the block. See if you can find a logical pattern of where the leak is coming from. For all you know, it could be a fuel leak and its not drying until it hits the bottom 1/2 of you heads, causing the corrosion you see.

Also, if its leaking outside the head, its leaking inside the piston area too. When you start the bike, put a white T shirt over the exhaust and see what you catch. If your getting something different in the vertical cylinder then, you know its the problem. Also, dump your coolant and oil to see if there is any water in the oil and any oil in the coolant.

Pulling the head off is straight forward, but its a lot of work. You'll need the proper tools, a decent torq wrench and LOTS of time. New gaskets arn't cheap either and getting the proper size is a whole other ball-game. Doing it half-assed is easy... doing it right the first time, its almost impossible. ;)



 
#6 ·
Thanks for cheering me up Tye ;) I'm hoping it's just the gasket but there's usually something else.

It is definitely leaking at the gasket though, the dots on the valve cover are just splashes, in fact the shock, hugger, swingarm etc are all stained and it is coolant not fuel. The coolant and the oil are both still clean and I've not lost enough coolant to show a drop in level so I'm hoping that I'll be lucky, plus there is no coolant higher up and the hoses etc are fine.

Also the bike runs fine, steady temperature, as smooth and powerful as before (as far as I can feel).

I've picked up a head gasket set, that includes head & base gaskets, valve seals, O-rings, inlet manifold gaskets etc as it was 'only' twice the price of a head gasket on it's own and apparently the new design metallic head gaskets are of a different thickness to the old composite ones on my bike (thinner head & thicker base gaskets) so I need to swap the base gasket and the head gasket to keep the same cylinder height.

I've stripped the bike and will get the heads off tomorrow (once I've sorted a head nut tool), then I need to see what else might need replacing? probably the belts (have done around 3k miles in 12 months) but I'll evaluate that when they're off. I'm hoping to be back up & running sometime next week but I'll probably be asking for more advice soon.........

:)
 
#8 ·
You can take the head off without the proper tool, in fact I hate the stupid aftermarket tool, its a piece of junk. I'm pretty sure the nuts are 15mm, so just get a wrench and take those suckers off.

Once your in there, you need to measure the cylinder barrel's mating surface with the head and visa versa. Take a piece of glass and put the head on it and do the same with the cylinder barrel. This way you can make sure nothing's warped. Then, check the studs themselves. If they are black all the way down, then you're probably kool. If the studs change color from top to bottom, you've got some bad studs. They are designed to stretch and if they were over-torqued by somebody in the past, they change color and can fail. If they look good, make sure they are tight before re-assembly, but be careful to meet Ducati torq spec's on them. You've gotta take the pistons off the rods to put on new base gaskets, so that adds another challenge. The pistons have to be re seated in the cylinder barrels, which takes some patience and some assembly lube or motor oil. Then you've gotta re-assemble the entire thing to check squish. Its SUPER important to check squish and make sure its correct. I had to remove my base gaskets because my squish was 1.09mm with the new gaskets, which is WAY too much. Also, don't forget to throw grease on the head stud threads when you re-assemble. Thats one step a lot of people forget about and it can easily cause a rod to break due to bolt sticktion.

If you don't have a desmoquattro service manual, I'd pick one up. It would take me a month of writing to detail the process step by step.



 
#9 ·
Just my cents worth.

Looks like it is coming from under the cyclinder, under pressure hitting the engine block then splashing back and running down, otherwise why would it splash to the outside of the exhaust manifold? would be interrested to know. great tips tye.

Either case its a head removal and poss cylinder too.
Best of luck

Nico
 
#10 ·
it's not uncommon for them to leak under the vertical exhaust port. i'd try retensioning it first - it may help stop it for a while at least.

the old composite head gaskets stick to the heads and cylinders like super ruper duper sticky shit - you might not have a chance in hell of getting them apart on the bike. and thats not even considering the corroded in dowels on two of the studs. it can be a really crap job - you'll end up with a thin sharp blade trying to hammer it in between the two and only damage the gasket. it's not fun.

most likely the cylinder will pull off with the head. remove the plug to make it easier. you'll need to at least reseal or replace the base gasket as well. the old head gasket as yours has now is 78610055A - you might still be able to get it. you can run them without base gaskets and have squish around 1.00mm.
 
#11 ·
I got the head off and as you say the cylinder came with it, it took some 'engineering' (rubber hammer etc) on the bench to split them, one of the dowels in particular was tight.

The leak is very minor and as you suggest it looks like torquing the head may well have worked.

Amyway I'm now cleaning everything to fit the new gaskets and have measured that the overall gasket thickness is slightly less for the new set; Old gaskets measure 1.2mm head, 0.4mm base and the new gaskets are 0.4mm head and 1mm base, I assume this thinner gasket will be OK and just give me a slightly higher compression?

Which brings the next question; I was going to just change the rear cylinder gasket as the front is not leaking (apparently the rear cyls are more prone to this fault?) but if the gasket thickness is less than the front, will an 'imbalance' of compression (assumed) have any undesired effect? Should I also change the front gaskets to match?

:)
 
#12 ·
I never thought about the age of your bike... I forgot about those shitty-ass gaskets they used. I'd replace BOTH gaskets, so you don't end up doing one now and having the other one go at some point in the future.

You've gotta measure squish. No two bikes are alike and a gasket thats compressed is not the same thickness as a gasket on your bench. The old gasket is compressed, where the new gasket isn't. You've got a small bit of room to work with since you've probably got steel rods. Minimal I'd suggest putting the squish at is .90mm. With that being said, the most I'd make it is 1mm or you'll start loosing compression. So that means you've only got .1mm to play with, which isn't that much.

So measure squish, do it properly and cross your fingers. Looks to me like the new gaskets are gonna be too large, but thats guessing. I've been pretty successful at using solder to measure squish. The stuff I used was exactly 1mm thick and its cheap to buy. Also, I'd buy Ducati tri-seal and use it to seal the base gasket and throw a bit on the head gasket. Don't forget what I said earlier about using grease on the head studs... I can't tell you how much pain that will save you in the tightening process.



 
#13 ·
Well the new gaskets are 0.2mm thinner than the old (rear cylinder gaskets), so whatever the squish setting it will be tighter than before (engine guy at JHP reckons approx 1.3mm is normal from the factory), I can't see the new gaskets compressing any so unless it's way out I'll probably leave it as it comes - it's fast enough for a roadbike.

I got the rear cylinder/head/case/piston cleaned up, ready to reassemble but I need a to get a bigger piston ring compressor. I think I'll do both cylinders whilst I'm there, if not the other'll probably blow next week!:rolleyes:

:)
 
#14 ·
1.3mm is HUGE! Ducati corse runs around .85mm, my stock 748 was 1.09mm and I'm currently running .95. A sure way to loose a lot of compression is to run it at 1.3mm.

The replacement gaskets will squish quite a bit, I was shocked how much my copper gaskets changed, once they had been through a heat cycle.

You don't need a ring compressor to install the pistons. I actually prefer NOT using one because if you use your fingers, you can make 100% sure you didn't destroy a ring, putting the piston in the cylinder. I've seen friends go down the ring compressor path and end up finding out months later, there rings were destroyed.



 
#15 ·
So I got it all back together today, started up fine but I have a problem; there is an oil leak from under the rear cyl base gasket, front cyl looks fine although I only ran it for a couple of minutes.

On close inspection it appeared that the gasket wasn't seating properly just by the O-ring that seals the hole in the crankcase (that goes nowhere in the cyl head).

Now when I initially assembled this head on Saturday that particular stud (rear right on rear cyl) didn't seem to tighten 'right' before reaching the correct torque it seemed to turn too far, too much. I did actually remove it and examine everything which looked to me, at the time OK so I re-assembled it and it seemed to torque fine this time. The only thing that looked 'wrong' is that it sits about 2mm further out the head than all the other studs (I don't know if it was initially like that) so it looks like it may have stretched and/or gone 'soft'.

I have now dismantled the rear cylinder again but before doing that I re-checked the torque settings and it was OK (although engine was warm - so could be a bad reading) but something is not right, unless the O-ring was preventing the head from seating? - it is thicker than the gasket but at that torque it should have squashed sufficiently and it was in the correct place & didn't look to have been 'pinched', plus this base gasket is thicker than the original which had no oil leak. The O-ring looks fine so I don't think it was leaking plus I had 'three-bonded' the gasket on both sides.

So now I have it all apart again and I'm wondering what to do next? - if the stud is stretched and it would appear that it might be due to being longer than the others then why was the torque still OK? surely a soft O-ring couldn't have stopped the cylinder seating at the specified torque?

Do I really need an O-ring there? there's no O-ring around the other oil holes (although they are further into the cylinder) why is that hole there anyway? it doesn't go anywhere and there isn't one on the front cylinder - looks like I might need a new stud, if so hopefully none of the others will do the same trick.

I'd rather be riding it.......

Any ideas?

:)
 
#16 ·
I had the same oil leak before on a 748, yet after sealing that oil ring with sealer "better" my rear cylinder leak went away, yet I was told that it "the o-ring" was not necessary but my 748 wanted it.

Cheers
Mark
 
#17 ·
I'm impressed with your apparent patience, and appreciate hearing the details of what you are going through. I'm wondering if these problems (cylinder coming off with head, strange o-rings, etc.) are common to xx9 bikes as well, or is this something special to 748s?
 
#18 · (Edited)
Remember when I talked about head studs earlier? Yea, they are a HUGE problem. When you do any work to a set of heads, especially ones that don't go on and off every weekend like mine do, you really need to re-torq the studs or replace them. Look at the color of the studs, are they uniform or are they different. If they are the same color, they've probably not stretched too much and could be used again. When they've stretched too much, you can notice a color difference, the lighter it gets the more they've stretched. The studs should be BLACK, not gold or silver in color. If they look ok, use two of the head bolts and without the head on the bike and the studs exposed, screw them on to the stud and lock them into each other. Then take your torq wrench, pull the studs out and re-thread lock'em, then put them back in. This way you can make 100% sure the studs are OK and are all at the same height. Your studs won't back out easily, but they can break. Ducati recommends replacing the studs, though I don't know at what service interval...

In terms of gaskets, seals, yada, yada, yada... The base gasket goes on 1 way and you probably have it wrong. There is a little indent in the casings, sometimes colored with a red dot, other times not at all. That indent is covered by a little lip on the gasket. Once you've got things aligned, Ducati tri-seal is your friend, don't be sparing, cover the sucker.

The head gasket needs tri-seal too, but not very much. I just put it around the oil holes and around the outer edge. The gasket should look like somebody took a grey crayon and rubbed it around the edges, just a hint of seal.

Re-assembly... Base gasket and cylinder is first obviously. I prep the head BEFORE doing the base gasket, so I can do the cylinder and then throw the head on right away, so not too much dirt gets in there and the tri seal isn't completely dry before I lock it down. Grease the snot out of the head studs and bolts, so they are very easy to move. Then tighten down the studs by hand using a 15mm wrench, much easier then using that stupid tool. Go VERY slowly, do a star pattern and take your time. Once you've gotten them hand tight, check how tight they are using a torq wrench. They should be at around 12 lbs by hand. Go once around and check them and then bring them all up to 25lbs VERY SLOWLY. Once they're at 25, take a break, wipe down the tri seal residue, clean up the heads a bit externally because once that sealant dries on stuff it can get messy to clean up. Also, clean up the grease you put on the bolts/studs so you can see the top of the studs peeking through the bolt. Take red nail polish or some paint and mark the top of the stud and the head bolt. This way you can tell if the stud is moving with the bolt or its just the bolt. Then its time for the big one, torqing it down to 40lbs. I go so slowly whilst doing this, you can hardly see the nut move. At the same time, I check for stud movement. This is VERY important to the re-assembly process. You wanna make sure the stud doesn't move AT ALL. If you get a small soft feeling, thats ok, as long as it tightens down to the proper spec. If it doesn't tighten down, buy new studs... DON'T attempt to ride the bike, don't even think about doing anything, just replace'em. Once you're locked down at 40lbs, your not even close to being done yet.

Obviously, oil and coolant need to be added and in that process you can test the motor for leaks. I usually clean up the block to make sure I can see leaks. Run the motor in the garage for the coolant addition process and then ride it around the block, get it up to 180 degree's or more. Then bring it back into the garage and check for leaks. If there arn't any, you're good to go for at least 100 miles. Once you've passed 100 miles, you need to re-check the head bolts. The new gaskets are kinda weak sauce, they need to be re-tightened and checked before you can call this process over. Take out the torq wrench again and give'em all a slow torq. This is when you really know if something is wrong. If they all tighten down to spec, your done! Wipe your hands off and call your bike running again.

So... Sorry for the speech, I just wanna make sure you don't trip in the same holes I've been down. This is a VERY easy process, I've done it 8 times now with 100% complete success and know what its like to have bad head studs... took me 2 hours to remove a broken one from my block! Thank god it wouldn't tighten down.

BTW: NO O RINGS!!! Thats for the older gasket design only.



 
#19 ·
OK so I re-assembled and all is well, the problem was the O-ring - on 916 and older 748 there is a hole under the cylinder that is used as an oil feed for 2V heads (the 900SS etc used the same crankcases), I understand that it was not drilled in the later 4V crankcases - this is where the O-ring fits inside the hole in the gasket and indent in the crankcase to stop the oil leaking past the edge of the gasket - the hole is very close to the edge, so there is not enough gasket to seal it.

There was an O-ring around this hole with the original setup and there should have been a new one in the gasket set, which is thicker to allow for the thicker base gasket. However the O-ring was missing from the set so I (mistakenly) re-used the old one which looked good to me but as it is too thin it was not sufficiently compressed to seal properly, hence the leak.

What I have done to overcome this leak;

1. Tapped the hole with a 4mm thread and loctited a grubscrew in there to plug the hole.
2. Fitted a thicker O-ring anyway.
3. Filled the O-ring rebate/O-ring with three-bond.

That oil hole will never leak again.

I then re-assembled as before and now I have no leaks.

Tye, there is probably no oil hole in your crankcase which is why you don't need an O-ring, those of us with older bikes have to deal with it - I have taken the 'belt and braces' approach to prevent it from leaking.

Regarding the head stud; it is jet black all the way down, like the others with no signs of stretch but appears to have been screwed approx 2mm less into the crankcase, it was tight in there so I didn't want to disturb it.

Thanks all for the advice.

:)
 
#20 ·
Tye, there is probably no oil hole in your crankcase which is why you don't need an O-ring, those of us with older bikes have to deal with it - I have taken the 'belt and braces' approach to prevent it from leaking.

Regarding the head stud; it is jet black all the way down, like the others with no signs of stretch but appears to have been screwed approx 2mm less into the crankcase, it was tight in there so I didn't want to disturb it.
Yea, I've also never seen in the older head gaskets in person... but I was told you needed to use o rings in conjunction with those gaskets. Oh well, learn something new every day. :D

If you could tighten down the head bolts, your fine. The studs seem tight, but I found tight, isn't tight enough, they can still come loose, especially when you take heads on/off all the time like I do :D

Glad you got it working!



 
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