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moto64

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Next step if there is no gain would be the exhaust and carb like Mike suggested. alternative you could see about opening up your port timings too. Adam bower at sole power could probably make quick work of it if you want to send the top end to him.

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I'd lay money down that the deck height on the piston is to short causing the squishing issues. Not all pistons are manufactured equally...

 

If you no longer want the original head, I could use it.

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It's yours. I don't see myself putting it back on. Let me know where you want it sent and cover the postage when I get it out: probably whatever the fixed priority box runs. FWIW the volume of this head is 34 ml. Maybe that means something to you but I have nothing to compare it to. Currently I have an SHI/20 carb on there, stock air filter set-up and a stock exhaust.  As I might have said I am not a purist but I  generally like to do a restoration to original condition/specs just to see what something was like when it was new. After that it depends on how impressed or unimpressed I am. This darn bike should run as good as it looks or the hell with it.

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If you're reading squish clearances like that, you could be losing 15-20% of your power right there. One thing you could try first, although difficult with the engine in the scoot, is to measure the deck height. That will give you a base to work with. If the deck height is, say 1.8mm, then it won't matter much what you do with the head. Bare minimum will always be 1.8mm. That gap would have to be closed up one way or another. Deck height + gasket thickness + head recess - torque compression = squish clearance. None of that is very easy to measure accurately, but it will give you a ball park of what you'll get when you bolt it together, rather than just assemble and hope it's right.

It's common to find the head contour not match the piston dome on stock heads. If the deck height is within range, then I'd get a new head cut, or use a newer type 200 head. The trouble with that is that a new 200cc head may still be wrong on the contour. Every head I do gets matched to the piston being used. I would definitely start there before I went altering a rare barrel. 

 

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 Ever have one of those "Ah Ha !"  moments ? Using my molding profiler ( I am a cabinet/furniture maker) I got this . Clearly shows relationship between head and piston. I measure ( as close as i can) the deck height at .8mm.

DSC02762-001.JPG

DSC02763-001.JPG

IMG_20170822_0002.pdf

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With a deck of 0.8, then with a 0.5 head gasket, you can get within range of 1.3mm squish. Do you have another 200 head you could check the profile on?

Alternatively, you could run no head gasket, have the head cut with a recess to get 1.1/1.2mm squish. Although in this case, I wouldn't recommend going through that trouble for such little gain.

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I only have this original head and I can't find the original piston to see if it had a dome top radius that more closely matched the head so that point is moot. If you look at the pdf pic I attached you can see the current relationship and why the compression's so low. I am ordering a later offset 200 head and I'll see how it relates.

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Think we are explaining deck height differently Adam.

Deck height to me means the measurement from center of wrist pin to the top edge of the piston. Perhaps compression height would be a better definition.. A 1.8mm deck height would be a tiny piston.

Nice job on the profile tool,  they work perfectly for that job.

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Not quite certain of the term myself , I looked it up :

" Block deck height is the measurement from the centerline of the main bearing bore to the flat part of the block deck where the heads bolt on. ......... The block deck height is not to be confused with piston deck height, which is the measurement from the piston crown to the block deck where the heads bolt on, with the piston at top dead center. " 

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1 hour ago, dirtyhandslopez said:

Think we are explaining deck height differently Adam.

Deck height to me means the measurement from center of wrist pin to the top edge of the piston. Perhaps compression height would be a better definition.. A 1.8mm deck height would be a tiny piston.

Nice job on the profile tool,  they work perfectly for that job.

You're right, we mean different things. Wiseco, wossner, and af use the term compression height when talking about wrist pin to piston crown. I've always read the term deck height when referring to the lip between piston crown and top of barrel. 

Either way is fine with me. If you say a 32mm deck height or 0.5mm  deck height, I'd know what you meant either way. :)

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I thought deck height was a relationship between the piston crown and crankcase mouth, at BDC. It is impossible to measure deviation between cases from crankshaft center line and crankcase mouth without more sophisticated tools, so most people just measure visually by watching to see how far (or in this case, likely, how not as far) the piston sticks out of the top of the barrel. So this is what I would propose. We already have an idea of what your head looks like. Can you also post a picture of the piston at TDC?

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8 hours ago, moto64 said:

 Ever have one of those "Ah Ha !"  moments ? Using my molding profiler ( I am a cabinet/furniture maker) I got this . Clearly shows relationship between head and piston. I measure ( as close as i can) the deck height at .8mm.

DSC02762-001.JPG

DSC02763-001.JPG

IMG_20170822_0002.pdf

That is a glorious tool!!!!

 

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1 hour ago, upjettr said:

That is a glorious tool!!!!

 

You really see the difference between the piston and the head profile there. Nice job. 

 

If it were me I'd have the stock center chamber head recut to match the piston profile better. From there the compression would go up and you'd gain some HP.

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Mike, it seems to me that if you tried to change the angle of the outer part of the head so it was shallower to match the piston, you'd essentially end up cutting the bottom of the head off, or at least end up with a very thin flange to fasten to the cylinder.

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I would have Adam Bower do a new head for you. And I would sell the original one. Or you can give it away to someone who will just sell it later.

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2 hours ago, moto64 said:

Mike, it seems to me that if you tried to change the angle of the outer part of the head so it was shallower to match the piston, you'd essentially end up cutting the bottom of the head off, or at least end up with a very thin flange to fasten to the cylinder.

it would thin down a bit but would be fine. Upjettr has the easier solution.

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So, answer me this if you will please : What would be the situation using a new, later style 200 head with the off-set chamber if I can get the squish down and the compression up? Mr Sticky seems to think it is a performance improvement over the original. What exactly would Adam provide that was better ? What is the value of the original head  and why ?

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I'll answer 1:

Adam can cut the squish zone to match the profile of your piston. The later offset chamber is supposedly better so if you want it perfect, buy a new head and have that one done. Since the TV200 is so desirable, I would not alter the original head as it's worth more unmodified. Also if the center squish head is not as good as the offset head, it would be better to modify to better design versus modifying the earlier, inferior design.

You can also just toss the later head on and set your squish and see how it works before getting it reproduced by Adam. Would it be better to get it reproduced? Yep, but I wouldn't bother unless I was having him blueprint the jug, intake, exhaust and piston. That way you know you'll have everything absolutely perfect and performance would be optimal.

No clue on value but TV200 stuff is always big money compared to more common parts.

All of this goes back to what Mike said: the TV200 gearbox is anemic.  Going through all this trouble and keeping that in the engine is only going to disappoint.  Do all this and swap it for an SX/Jet/TV175 gearbox and you'll be a happy dude. 

Also I wouldn't sell any of the tv200 specific parts like the gearbox or head. If you ever sell it, it would be worth more if that was included as anyone dropping $12k+ on a Lambretta is going to be a real anorak about that stuff.

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If you take meat out of the head to match the piston, compression will go down.

 

What make of piston are you using? What is the compression height of it?The TV 200's I have built have had plenty of get up and go using the original head.

As Upjetter said, any chance of a picture at TDC? Do you still have the original piston?

It is my understanding a stock TV 200 had issues because of too much compression, using the central head and a stock piston....which is what you have, except for the replacement piston. My money is still on the piston being wrong as that is the only part in the equation which is not original.

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I can't find the original piston which is odd because I have, for some reason,  kept pistons from all sorts of motors  ( a 1hp 1930  Evinrude outboard?)  so I don't know what it looked like. Sticky states that the later off-set head was a performance improvement but says nothing about the early version being matched to the early piston. If the dome of the original piston was high enough to match the contour of the original head it would certainly interfere in a big way with a later head so you couldn't just upgrade the head without changing the piston. Right ?

Of all the receipts I have for this bike project ( a depressingly large number..) I can't find the one that includes the new piston, but it most likely came from Jet in Denver ( not SRS, ebay, amazon, rockauto or the like ), and I am assuming here that if I mate it to a new 200 head from them I should have a decent, base,  stock type of set up. Of course things can be modified from there. So, I will have the new head in a few days and I'll check it with my handy profiler and we'll see how it matches up. Here's another shot of what I have at TDC.  I did just have the cylinder off and could see the markings under the piston but didn't record them or pay attention. I can take it off again easily enough but I would rather just wait for the new head.Thanks.

DSC02764.JPG

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Yeah ? I attached this as a pdf before but here it is as a jpg. This is a tracing from the profiler and it is pretty clear why there is no compression with this set up. I will do the same with the new head when it arrives.

 

IMG_20170823_0003.jpg

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I'll chime in here as devil's advocate and just say that if you really want to enjoy riding this scooter, just set the whole top end on the shelf and get the RT225  kit. you can use your stock carb/exhaust, or you can upgrade those and still have a reliable (stock-ish) scooter that is actually fun to ride.

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Yup, might just go that way. But for now, if I can bump this thing up for the cost of a head and a gasket and make it at least satisfying to ride....

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