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Discussion Starter #41 (Edited)
Wow. Thank you so much for you lengthy response and wonderful help. I will do what you suggest and see what happens. I have a 900cc desmodue with EFI. The top of the intake valve did appear black, what little of it I could see through the spark plug hole. I will try to check closer next time I see it.

So you don't think that the addition of oil and the subsequent rise of 25 psi in the compression test is indicative of worn rings? That is a rise of over 20%.

I bought some new spark plug wires today, from Taylor, their spiral wound ones. They suppress RFI.
 

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I would say that’s a normal rise in pressure and a good indication your rings are just fine.

After seeing how bad the valve job was done on mine, you’re probably in the same situation - but until you verify it I’d try what I suggested first. If you have the build-up on the intake valves, well…….. The leakdown will help verify this. I tried reseating a couple of the valves before removing the heads but with no luck -- and I can see why.

I ground my valves today, only needed to remove between .0015” to no more then .003” (more like .0025 max if even that..) to completely clean them up. As the previous photos show, the area that was leaking is exactly what I saw when grinding the valve -- Low Spots on the face of the valve.

The problem is - as I see it, it wasn’t going to get any better by itself, and what I saw today pretty much verifies it. I doubt the valves would finally seat properly over time, just get worse. If they leak now (and they were leaking from the first time I looked @ approx 2000 miles or less - so probably from the beginning), the combustion will continue to blow past the valve seats and erode the valve face even more. The seats are EXTREAMLY hard, but the valves are relatively soft. If it’s just carbon build-up not allowing the valves to seat you might get lucky. It really does sound like it’s running too rich so that’s not helping. I was surprised how nasty my combustion chambers looked… :eek:

I did get an occasional backfire into the intake - but not very often at all - also a very occasional hick-up but nothing to be concerned with - but the bike ran GREAT!! Real strong!!! These problems may explain why I had those occasional symptoms. Hard to believe it’s in such bad shape to run so damn good!! Can’t wait to get a good valve job on it!!!!
 

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Discussion Starter #43 (Edited)
I would say that’s a normal rise in pressure and a good indication your rings are just fine.
OK, thanks. What do you use to hold the engine still while doing a leak down test?

Also, are you saying you didn't do anything about the seats being too wide in your case? It sounds like you lapped the valves only.

I think I have a cold so I may not get to this for a while yet.
 

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I made an engine turing tool that I can attach a 3/8” ratchet to (I don't leave the ratchet attached during this test just in case, but I can leave the rest of the tool bolted to the case - plus it seals so I don't have to be concerned with debris getting in the engine). But: Since the cams were out I let the piston go to BDC. I tried to get it to perfect TDC (rod straight up) but only a couple of times because it didn’t matter in my situation so why fight it?! Instead of trying to hold the crank, work at getting the piston directly to TDC. If the rods at either side of TDC - not straight up - but the piston hasn’t moved that you can feel, as soon as you pressurize it - as you know will drive the piston down. The rod needs to be straight up. Not all that easy to do especially with decent compression. Another option is to remove the belts (grant you - not a great option) and make sure ALL the valves are closed in both heads, then it doesn’t matter if the piston is at BDC for the test.

Another option would be holding it at the clutch basket - just make sure you know what direction the engine is apt to turn unless its firmly bolted to something.

Stay well.. no fun being sick...
 

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Also, are you saying you didn't do anything about the seats being too wide in your case? It sounds like you lapped the valves only.
I missed your question -- Once I get the guides installed I’ll be cutting the seats with 5 angles. Lapping the valves in will only match the valve to the seat but you’ll still have too wide of a seat. So the only way is to cut it to shrink the seat width. I do a interference cut. Valves cut at 45 degrees. I did a small 20 degree back cut on the valves - this helps remove the sharp edge turning it into a kind of radius.

As for the seats: I cut the seat at 46 degrees with a top cut of 31degrees to position the edge of the seat to the valve, then a 15 degree to knock the high edge off. The bottom cut is at 60 degrees to create the seat width and then 75 degrees to knock the low edge off that cut. If you really want to get trick you blend in all the edges turning them into one nice radius .. I’m going to pass on that part. If you slip and mess up hitting the seat you have to go back and re-cut.. With the interference angles there is no need for lapping.. It creates a perfect seal every time. Once run for a short period or even just slapping the valves into the seat a few times will match the angles to each other creating a clean seal, not a rough ground seal like you get when lapping.
 

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Discussion Starter #46 (Edited)
OK, I did a leak down to the best of my ability so far. I used low pressure (60 psi) since I only have a little pancake compressor and it's so loud when it runs I can't hear where the air is escaping. But, with the other cylinder spark plug out, air was coming out of there and out the exhaust. I made sure I was as close to TDC on the compression stroke as I could determine. There are so many marks on the stator in the window that it's hard to tell which one corresponds to TDC. But, I could see when the intake opened, so the next stroke was the compression stroke. So, I used TDC there, right after the intake valve opened.

If air is escaping through the other cylinder, I assume this means worn rings?

Pressure was set at 60 psi. It goes down to about 45 psi when I connect it to the cylinder. I believe that's a 30% loss, which is a lot.

I was able to look at one intake valve a little bit. The seat is as wide as yours, but there was only a little bit of carbon on the top of it. The part of the valve sealing surface that I could see looked clean to me.
 

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Finding true TDC

This is from Ducati-upnorth.com/tech/camtiming.php

Finding the Exact Top Dead Center. Before you start you will need to determine the piston TDC accurately so that you can set the degree wheel to reflect piston timing. Whilst the crankshaft is moving a few degrees either side of top dead center the piston is virtually stationary so any measurement at this point will not be accurate enough for the purposes of cam timing. The accurate way to measure TDC is by using some type of ‘Positive Stop’ device. The idea behind this is that if you can stop the piston at the same position on its stroke both before and after TDC and mark the degree wheel at both points then TDC must be exactly half way between these two marks on the degree wheel. You can make your own positive stop device with an old spark plug body drilled out and a piece of threaded rod or bolt inserted and fixed in place. See references at the end of part 3 for articles on making and using this type of tool. Attach the degree wheel to the crankshaft. You will need some way of turning the crankshaft without upsetting the degree wheel either use the factory disc tool, which I found had too much play, remove the side cover so you can get a socket onto the crank nut or select 5th gear and turn the rear wheel. Attach the pointer to an engine cover screw so that it lines up with the degree readings on the edge of the timing disk. Remove both spark plugs and using a blunt probe locate approximate TDC on the first cylinder you wish to check. Move the timing disk on its bolt so that the pointer lines up with 0° then tighten the disk so that it cannot move on the bolt. Turn the engine forward slightly so that you can screw the positive stop device in without hitting the piston. Then carefully turn the motor back until the piston touches the stop device. Mark the degree wheel next to the pointer then turn the engine forward through almost a full turn until the piston again just touches the stop device. Mark this point on the degree wheel then calculate and make a third mark exactly half way between the first two. This is the real piston TDC point, so remove the stop device and turn the engine until this mark is next to the pointer and now your engine is exactly at TDC.
You will probably find that the mark does not coincide exactly with 0° on the degree wheel due to our first setting being approximate so to make life easier during timing measurements bend the pointer slightly so that it now points to 0° (Do Not move the engine!). Rub out all your marks on the wheel and go through the whole process again using the stop device and now you should find that the third mark lines up exactly with 0° on the wheel. Make sure that the engine is at TDC with the degree wheel reading 0° before continuing! Note that if during any part of the measuring procedure you suspect that the degree wheel may have moved in relation to the engine then recheck TDC using the above method before continuing.
 

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Discussion Starter #48
That's a good way to do it. I just stuck a thin hex tool in the spark plug hole and felt when it was at TDC. As long as the valves were closed, that's close enough I think.
 

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That's a good way to do it. I just stuck a thin hex tool in the spark plug hole and felt when it was at TDC. As long as the valves were closed, that's close enough I think.
Probably - valves closed is what you are seeking

My desire to now true TDC is for dialling in cams and therefore needs to be accurate.
 

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Discussion Starter #51
Or, leaky exhaust valve if the exhaust of the other cylinder is open.

Tom
Ah, good point. The other leak path was the exhaust. Actually, now that I think about it, when I stuck my finger in the other cylinder, the leak out the muffler increased. Leave it to an engineer to stick his fingers into things! So, at least one leaky exhaust valve. I didn't bother testing the other cylinder.

I just hope that the piston didn't slip far enough when I put the pressurized air into the cylinder that it cracked open the exhaust valve. I thought they didn't open until BDC on the compression stroke?
 

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Ah, good point. The other leak path was the exhaust. Actually, now that I think about it, when I stuck my finger in the other cylinder, the leak out the muffler increased. Leave it to an engineer to stick his fingers into things! So, at least one leaky exhaust valve. I didn't bother testing the other cylinder.

I just hope that the piston didn't slip far enough when I put the pressurized air into the cylinder that it cracked open the exhaust valve. I thought they didn't open until BDC on the compression stroke?
Long before, depends on the valve timing.

For example, my LeMans, when it had OEM cams, opens at 58 degrees before BDC (looking at the manual in front of me)

Tom
 

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Cam timing

Ah, good point. The other leak path was the exhaust. Actually, now that I think about it, when I stuck my finger in the other cylinder, the leak out the muffler increased. Leave it to an engineer to stick his fingers into things! So, at least one leaky exhaust valve. I didn't bother testing the other cylinder.

I just hope that the piston didn't slip far enough when I put the pressurized air into the cylinder that it cracked open the exhaust valve. I thought they didn't open until BDC on the compression stroke?
This is a good article about cam timing and will provide answers on what/when valves open and close.
 

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This is a good article about cam timing and will provide answers on what/when valves open and close.
OOPS - this time with the attachment!
 

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Discussion Starter #55
I think what I want to do is pull one head, inspect it, re-lap the valves myself if it's true they are leaking, check the seal with a vacuum cleaner, put it back together and see if the compression comes up. If it does come up to spec, then I'll do the other head also. Can you get the head for the horizontal cylinder off without taking the engine out of the frame? I can't tell if the front wheel is in the way. I'm not going to worry about a fancy 5 angle valve job. I could even replace the guides myself. I just need the special drivers.
 

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Horizontal Cylinder

Hello there
Yes you can get the head off but you have to lower the engine about 40cm.
In this thread its explained well enough for me to do it. I had to do it twice as the original gaskets did not hold. Now I used silcone.

Regards
Arnego2
 

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Discussion Starter #57
Hello there
Yes you can get the head off but you have to lower the engine about 40cm.
In this thread its explained well enough for me to do it. I had to do it twice as the original gaskets did not hold. Now I used silcone.

Regards
Arnego2
I think I'd rather just take the front wheel off.
 

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I think what I want to do is pull one head, inspect it, re-lap the valves myself if it's true they are leaking, check the seal with a vacuum cleaner, put it back together and see if the compression comes up. If it does come up to spec, then I'll do the other head also. Can you get the head for the horizontal cylinder off without taking the engine out of the frame? I can't tell if the front wheel is in the way. I'm not going to worry about a fancy 5 angle valve job. I could even replace the guides myself. I just need the special drivers.
I don’t blame you for not doing the 5 angle (you asked) - its just that I have the equip (something I used to do all the time) so why not reap the benefits of it? I know that doesn’t help you any.

I’ve attached the maintenance manual - although out of the 916-996 - but look at what they say about the seat width. They don’t say how to correct it in this version but my other manual (not PDF) shows using a 60 degree. Maybe they did a better job on your’s and you won‘t have to worry about it. If not you might consider at least a bottom cut of 60 degrees to correct the width of the seat if you find there is no definition to seat width, otherwise you’ll still have the problem as far as wide seats go and the downside of it. If the guides are loose it will allow the valve to wobble into the seat before actually sealing (the exhaust will show the worst side of wear - also the exhaust valve stem is usually a bit smaller in Dia.). I’m going with Guy Martin’s Manganese Bronze Guides - pricy ($30 ea) but better material then stock I think - but will last WAY longer. Haven’t priced stock - don’t want to - I want to be done with it.

If you do replace the guides yourself you’ll need to heat the head up and be quick while removing. Even faster during install since same process but you need to freeze the guides and heat transfers FAST!

One note on the guides: They usually require an oversize on the OD. Once installed you’ll usually need to size them to proper clearance as they are usually undersized. Ball hones work well.

Attached are some shots of what a valve looked like before and during the grinding process.. Note the low (leak) area.

Still though - try the Seafoam first… may save yourself a lot of work - or at least delay it… lean that puppy out…..
 

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