Thermal coatings

[Spaceclam]

So one option i am mulling around in my head to help with the pinging on the bike is a thermal barrier coat on the combustion chamber (just the head) as well as valve faces, and piston faces. But a question has dawned on me, that i cant seem to get a straight answer to.

Will coating things REDUCE pinging due to the lower head/piston temps, or will the barrier INCREASE combustion chamber surface temps due to less heat transmission, (even though the heads themselves will be cooler) and make pinging worse?

I will have more details of the temp sensor as well as swapping the ECU hopefully this weekend, but after another run on the highway at 65 degrees, it looks like the heads see about 270F, and the block sees 200F.

Of course, if i have to pull the heads i WILL check squish and all.

 

[Christofero]

No doubt the state of the art has changed since I played with these things but I would solve your 'Pinging' problem before I started coating things. Your problem may not be unique but I can't believe that Guzzi would design the engine to be that close to detonation so more than likely you have a fixable problem

The standard causes are:
Too lean (air leak, pump pressure too low, wrong setup, sensors confused and telling the motor to put in too little fuel) A dyno with a four gas meter is the best/fastest way to find out what is happening here.

Too advanced for the available fuels - knock back the timing until it seems happy

Too much heat (more squish helps plus more oil cooler)

Too much compression for the available octane.

Detonation is not to be confused with preignition - which is caused by plugs that are too hot. One thing that I did run into was sparkplug holes that had been helicoiled - the helicoil interfered with heat transference and on a racing motor no plug could run sufficiently cold to make things happy. This is typically ok for road motors.

Many years ago I watched some Judd engineers play with coatings on their F1 engines. From what I could see coatings had a marginal effect - I was never able to see any quantifiable numbers on the dyno. Also you now have the chance of microscopic particles flaking off and flowing through your engine. No doubt things have changed (Swaintech is pretty much the authority) but I think these things are for ten tenths performance and not really worth it on a road bike.

Ta,

 

[GuzziMoto]

Coating the combustion chambers and piston crowns ( I would not do the chambers without doing the crowns ) should reduce the combustion chamber temp before ignition. By not absorbing as much heat into the metal more heat would go out the exhaust valve and not into the next intake charge. The difference will not be huge but it may be big enough to make a difference. It depends on what is causing your detonation. Mine is definetely heat related but I don't know your bike. If it is heat related then it stands to reason that reducing the heat may solve the problem. There are other things you can try first. Coating will be a last resort kind of thing for me.

 

[Spaceclam]

Guzzimoto,
Is this from experience?

Pretending everything else is sorted, what other tricks would you try, in order to reduce temps?

-Andrew

 

[GuzziMoto]

Yes, with Ducati's. But coating the piston crown is pretty common nowadays (a few pistons come already coated from the factory) and coating the head is not uncommon. The principle behind it is pretty basic. The gains power wise are minor and that would explain others experiences with it. But we did it with our Ducatis as much for reliability as for performance. The reason you don't gain much power is because while reducing intake temp before the valve closes has measurable gains, once the valves close it doesn't really gain power from reducing temp. There is a small gain as more heat goes towards pushing the piston down but that is a small difference.
As far as other things to try? The AutoTune would be the first if you haven't already installed it, along with deleting the O2 sensor for the ECU. Richer mixtures lower temps and are more stable. Bumping the timing back a couple degrees while hard to do should lower engine temps and reduce the chance of detonation. Modern bikes tend to have too much ignition advance for proper running as more advance reduces emissions. From what I have seen Guzzi combustion chambers also do not have enough squish which also is bad and increases the chance of detonation. Squish causes turbulence in the chamber and that reduces the risk of detonation. As weird as it sounds, on my wifes V11 I had the heads and cylinders milled which raised the compression ratio but increased squish and the end result was less detonation. Guzzi's have had a tendency to ping at least since the V11 series and maybe longer. It is not a new thing and seems to be a design weakness. The 8 valve motors may be better in this repect as they have a modern combustion chamber design, but the Hemi style head of the 4 valve motor has issues. Another thing to check is valve clearance and timing. Cooler plugs are an option but I would try higher quality plugs first. Cooler plugs should never be required on a street motor.

 

[Spaceclam]

Hmm. More squish. Interesting. What is the squish supposed to be on the modern heads, so that i might check it if i need to pull it off?

The fueling HAS been corrected, and the o2 sensor deleted. I have tried cooler plugs, which make no difference. Neither does octane booster. My neighbor races top fuel dragsters, maybe i can run some top fuel just for shits n giggles, and see what happens.

 

[GuzziMoto]

Yeah, you think it pings now.... Nitromethane detonates a bit harder then gasoline.
I set the squish up so that without a gasket the piston came just short of the cylinder deck. I forget what the final measurement I ended up with, but it was just short of what I wanted. On a street motor around 50-60 thou should be OK, on our race Ducatis we would run closer to 30. I prefer our 30-40 number even for street use, but that is me. Do some reading and decide for yourself. My attitude is the piston should come up and at full stretch just lightly polish the piston against the head. You can tell if this is working by the pattern on the piston crown. But setting a motor up like that requires more attention to detail, you need to clay the the piston. I ended up with around 40-45 thou if memory serves me and figured I could go further if needed later. Tighter clearance means more squish, but contact is bad. It's your bike, do what you want. When measuring deck height remember to include the thickness of the gasket in that number. That means with a 30 thou gasket you would subtract 30 from your target number when measuring the piston to deck clearance.
In the end, I don't think there is a "spec" number, but there is a minimum clearance to shoot for. What that minimum is depends on who you talk to. I'm a racer who likes to run it tighter, others will say you need more clearance. But really, in my opinion if a race motor only needs 30-40 thou, why would a street motor need more. I can see why Guzzi would build the motor with more clearance, it makes their job easier. But if 30-40 thou doesn't hit on the track it isn't likely to hit on the street either. But as I said, do your own research and decide for yourself.
As far as damage from detonation, first thing to check is the plugs. Typically you will see little specs of aluminum on them. that is a bad sign. From there you could check the ring lands (hard to get to), or the con rod bearings (the bottom ones are easier to get to). Also, as mentioned, the Guzzi Hemi design has a very small squish area around the outside of the piston. To me, the small size makes it even more important that you maximize what you have.

 

[Spaceclam]

Hmm, more stuff to check.

So when measuring squish, its the deck height on the cylinder, plus the gasket, plus any deck on the heads? I havent taken the heads off yet, i dont know what they look like.

Its interesting because i would think that a tighter squish would cause MORE ping. But then again, my background is only in mechanics, not tuning.

 

[GuzziMoto]

Squish refers to the area around the circumference of the piston where the piston and head almost touch. This pushes the air/fuel mixture out from this area as the piston approaches TDC and causes turbulence which is good. On a 2 valve Guzzi this is a small thin ring around the outside of the combustion chamber. If you look at most other modern engines they have a larger area of squish. One of the reasons many engines have higher compression ratios then Guzzi's (they claim like 10:1 but it is not even that high from what people like Mike Rich say) is that they have more turbulence in the combustion chamber caused by more and better squish.
Higher compression ratios increase the risk of detonation, but squish is not the same thing. They are related and tightening your squish clearance increases the compression ration slightly. If your motor has plenty of squish already then you may not gain enough advantage from the improvement in squish to offset the higher compression ratios effect on detonation, but 2 valve Guzzi's do not have plenty of squish stock so the improvement there can more than offset the effect of the slightly higher compression ratio.
On a V11 (and likely the same on a Griso) there is a thin ring where the piston comes close to the head. Then there is a beveled area (about a 45 degree angle) inside that which is about as large as the outer squish area. The bevel is to help direct the flow out from the squish area but it is a bit much. I had a machinist take almost half that off by milling the heads and then had the cylinders milled to get the dech height I wanted. I had to clay the pistons and add a little clearance for the valves but the end result was a motor with better power and no detonation (it did detonate before I started). Another way to go might be pistons from Mike Rich. I don't know if the ones he has will work on a Griso (I plan to call him this winter to see) but if they do they should improve your squish and compression ratio without so much milling. I was planning on looking into that this winter. Get a set of pistons, get them coated, and installed. But with my new baby (a '93 Daytona) needing so much love and attention I don't know if I'll have time/money.
Don't forget to try the easier more basic things first.

 

[Spaceclam]

I get it, but my question is this. What deck heights should i see on the cylinders, and what deck height should i see on the heads?

I am a machinist, and if given the proper dimensions, i can adjust things. What you are saying is that between the deck on the cylinders, plus the gasket, plus the squish area on the head, i should see about .040" to .050 between the piston tops and those areas. That could be accomplished by .04 on the heads, and nothing on the jugs, or vice versa. So how much should i see where?

The reason i am asking is because, if the simpler options fail, i'd like to already know what to do next.

I have already talked to mike rich, and he isn't sure the pistons will fit. That would be an expensive experiment, and they are a custom order. Since milling the heads is free for me, its kind of a no brainer if the squish gap is too high.

 

[GuzziMoto]

The bottom surface of the head should be the heads contribution to the squish area. That is the way it is on a V11 motor, and most other motors I've had apart. I would expect a Griso to be the same way. Your squish clearance (assuming the bottom of the head is the squish area of the head) would be the distance down from the top of the cylinder to the top of the piston (be sure to take into account the rocking of the piston and make sure the cylinder is torqued down) plus the thickness of the gasket.
If you go this route then after you are done it is a good idea to check valve to piston clearance with clay, again maintaining the same minimum clearance as with the piston to head, if not more.

 

[Spaceclam]

but if the piston doesn't reach the top of the cylinder all the way, than the squish area will be greater. The question is, i guess, if im going to set my squish to .050, then how much of that should come from my pistons not reaching the top of the cylinders?

I probably should have been more clear earlier. I really appreciate your help

 

[GTM®]

The piston will have a clearance (top of cylinder or not) to the head, this is what you clay and measure. Are you really ready to dice into your motor?

 

[GuzziMoto]

Assuming the Griso motor is like the V11 motor, your total squish clearance is the thickness of the head gasket plus the amount the piston comes up short from reaching the top of the cylinder. The head will be flat on the bottom with a bowl in it for the combustion chamber. The ring around the combustion chamber, which is slightly smaller then the bore, will be where your squish is. So the head gasket thickness plus the distance between the top outer edge of the piston and the top of the cylinder (obviously you do not count the dome of the piston) is your squish clearance. The gasket thickness is something you usually can't control (although on some bikes you can buy gaskets in different thicknesses) so you take the gasket as a fixed number and mill the cylinder to achieve the total number you want.
Measure the old head gasket for an idea of the compressed thickness of the head gasket as opposed to measuring a new, uncompressed head gasket, if it is a fiber gasket. Metal gaskets don't compress so you would measure the new gasket.
After you measure this, before you do any milling, please let us know what yours is stock. I wonder if a factor in some pinging and some not is differences in the squish clearance due to tolerance stacking.

 

[Spaceclam]

Todd, i dont want to mess with the motor. But if my squish is way off from what it should be, and if that could be the cause, well then, i guess it's what i do.

More than anything, i just wanted numbers to check in case i have to take things apart. We all know how fantastic the quality control is, and it's possible that they messed up. I would rather it not be so, but i am comfortable doing my own work if push comes to shove, provided i know WHAT to do.

That being said, it's my understanding that the cylinders are nikasil coated, and therefore must be milled from the bottom, yes?

Guzzimoto, A special thank you. Very few people have patiently withstood my barrages of questions. B)

 

[jr1967]

I have had two aftermarket cylinder sets(LM II and LM III) shortened to get the proper squish. In metric terms go no less than 1mm which is the same as a compressed head gasket, this will give you enough clearance for rod stretch and piston rock. I did not have to plain the heads for more compression, just fixing the squish raised compression to a nice 10.5:1 ratio.
On one set of cylinders I had the top ground off by 1.3mm on a cylinder head grinding machine; yes, the Nikasil flaked off a little bit and no, it did not matter since the piston rings don't get that high. It worked great for years. The interesting fact was that going from 83 to 90mm pistons, adding a cam, bigger headers, twin-plugging and mildly flowing the heads resulted in exactly the same output as before(57 rwhp), and that after reducing the squish to 1mm I gained 13 horse and actually had to use smaller jets. The latter definately highlights the increased volumetric efficiency.
After expert advise I had another set of cylinders shortened at the base(against my gut feeling) which resulted in the crank hitting the right cylinder bottom at high revs, with Nikasil chips coming off so I can not really recommed this. Ofcourse this was due to the amount of material taken off, since these were aftermarket cylinders that come with a huge squish. I don't really know a way to check if your cylinders don't go too deep into the engine so be careful or ask others on the forum.
Also beware of valve to piston clearance after the change in squish.
Good luck, JR

 

[Spaceclam]

How did your crank hit your cylinder after shortening? Do these have a sleeve or a bevel at the bottom or something?

 

[GuzziMoto]

The cylinder will have what looks like a sleeve (but it is not) sticking down into the cases.
I have usually had the top milled when shortening cylinders.

 

[jr1967]

Correct, doing it again I would go for taking material off the top of the cylinders like I did the first time; the flaking of Nikasil is no issue.
JR

 

[jr1967]

What I forgot to mention is that once the cylinders are shorter, the push rods might be too long..... Shorter ones are available, or sometimes you can just grind the threaded end of the rocker down so the adjuster can be turned out more(upwards) to compensate for the 'long' push rod. Setting the intake valve deeper into the seat for more valve to valve or valve to piston clearance will only make things worse, so most of the time shorter push rods are in order.
And ofcourse there is one more thing: the cylinder stud on the spark plug side will be sticking out more than before, preventing the spark plug from going where it should, so that needs shortening too......
Good luck, JR