Jump to content
moto64

flummoxed

Recommended Posts

About a year and a half ago I finished the resto on my 63 TV200. New 2nd over (66.4) piston and rings, cylinder bored for the piston by a pro . Rode it around quite a bit and then headed out on an 850 mile trip. Bike ran great, I thought, and I had no issues other than a very uncomfortable seat . (Someone had replaced the foam with something too thin. Fixed that when I got home.) I have never felt that this bike ran like a 200 should . My 180 V**** is quicker, faster, and smoother. I checked the compression and got something slightly over 90 lbs. I figured I had glazed the rings on the first leg of my journey so I gave the cylinder a slight hone to break the glaze ( it looked  great) and put in some new rings, gapped by the book. I know I haven't put too many miles on it and I do have non-synthetic oil in there, but it still feels under-powered so today I just checked the compression again. A hair over 90 . No symptoms of an air leak or any oil leaks as far as I can tell. I recently just re-pistoned/ ringed my smallframe V**** 135 Malossi after a soft seize and the compression is right up where it should be with all the power it should have. I also re-ringed the 180 V last year and it was great from the start. Should I just keep breaking it in and will the rings seat or what ???

Share this post


Link to post
Share on other sites

No . it was all stock except for the OS piston.  According to one source, compression should be 8:1 which would be roughly 112. so maybe it will just come up as the rings seat ??

Share this post


Link to post
Share on other sites

Derek is is talking about the squish between the piston head and the cylinder head when it's at top dead center. If it's too thick  or there is damage to your cylinder head, or a leak, you won't have any bang for your buck. Google search on Lambretta cylinder head squish band

  • Upvote 1

Share this post


Link to post
Share on other sites

Please keep in mind that the tv200. has a unique cylinder head, and that's very different from the Sx 200 cylinder head. Read the article in the link above and then go from there. If you do happen to have your cylinder apart,  post a photo of the inside of your cylinder head. I am curious to see the shape of it 

Share this post


Link to post
Share on other sites

Since Internet links don't always remain forever, I have copied and will paste the article as a post here. This is all mark broadhusrt info and it's copyrighted. So I hope I don't get trouble for re posting this. 

 

SETTING UP - Squish 


The squish band and squish clearance is very important and worth setting up correctly. The squish band basically controls power and how the engine will respond to the throttle. Pistons, con rods and crankshafts flex and expand. To allow for this expansion at TDC at high revs a gap is needed between the crown / dome of the piston and the cylinder head. 

This gap is called the squish clearance.

This gap should on assembly is usually stated as a minimum of 1.00mm and no more than 1.50mm (for most road going engines) The tighter the better for a race engine. A perfect squish clearance is a perfect gap between the piston and head at TDC and this gap should be uniform across its section. MB always cut our heads to suit the dome of the piston which will vary from piston to piston, we have various cutters to suit various domes. The Lambretta piston has the highest of all domes, Yamaha, Honda, Suzuki, KTM and other race pistons tend to use a flatter dome piston, these flatter domes effect compression ratios as well as squish clearances. Some dealers cut heads in a straight line which is easier to do on a lathe but only takes an average of the dome which we think can cause some running problems especially on high Lambretta domes. Others machine heads with the wrong dome so the squish band is not uniform and is tighter on the outside than in the middle, these give a poor compression ratios and poor squish bands and poor power. It's not unknown to have 1.00mm at the outer edge and 6mm in the middle. This is common when a head is fitted which was machined for a Lambretta piston with a big dome and fitted to a race piston with a flat dome.  

You can read more on head designs here.  

You can read on how to set up a cylinder here.

Lets presume this is a new rebuild and you are setting the squish up for the first time. To check the squish clearance fit the cylinder head, the head can slightly move on the cylinder studs but MB's machining methods mean that the head will locate quite central. Always use MB high tensile studs, thick MB head washers and MB special head nuts and extended head nuts these kits are supplied in all MB cylinder kits. Tighten the nuts using your hands and a socket, and tighten diagonally. Then slowly tighten diagonally using a torque wrench in steps to 10 lbs/ft, 15 lbs/ft and then 18/20 lbs/ft. Do not over tighten as it can and will distort your cylinder.  

The head is now tight and should have compressed whatever gaskets you have used or if any at all. Now the squish clearance can be checked. To do this you need some soft electricians solder approximately 1.5mm thick, if it's too thin double the wire over and screw it together to make it thicker. This piece of wire needs to be about 6’’ long. Bend the wire into a curve and feed it through your spark plug hole feeling it across the head shape so it touches the outer wall of the cylinder bore. At this point turn over the engine by hand using the flywheel. The flywheel will lock as the piston hits the solder wire, keep turning until the wire is crushed flat. Take the wire out and you should see a crushed piece of solder wire with a uniform flat shape. Some heads could be on a slight taper, measure at the tightest point. This is the squish clearance and now needs measuring with a vernier gauge or micrometer.

Ideally the solder should be done in the plain of the gudgeon pin, if you do it from the side plug to the exhaust port the piston can rock and give a false reading but to be honest I have always done it this way with no problems providing you never drop below 1.00mm. I've checked this many times you may gain 0.10mm on the reading through rock on a 70mm piston. So a 1.00mm squish allowing for rock is actually 0.90mm and this works perfect, remember 1 - 1.50mm is safe, anything over 1.5mm will loose power. Smaller engines down to 50 - 80cc with short strokes can run 0.5 - 0.80mm! If the head is close to the I.00mm and your on your final head rebuild it's worth bending the solder to get to 4 points of the piston to see if the head is off set. If you find it's 1.50mm in one direction and 0.80mm in the opposite then the head is bolted down offset, the head can be undone and taped in the direction of the 0.8mm this will increase the 0.8mm and decrease the 1.50mm to something like 1.10mm to 1.20mm on average which is fine. 

There are other methods to measure squish, some use plasticine which is messy, others tape two pieces of solder in a X shape across the piston so 4 points are measured, both these methods require removing the head again which will be false when it's refitted as the head can move in a different position if it's a standard type of Lambretta head assembly. But if it's a RT cylinder where the head is centralised in the bore or it's a spigotted head then these methods can be done.   

If you are lucky and the squish measures at its tightest point between 1.00 and 1.50mm then great you can carry on but if you are like me you want to be a perfectionist remove the head and cylinder and swap or leave out a gasket, this can be at the base or head. It may well be, you can not improve it at home without a machine shop, you may not even notice the difference between 1.00 - 1.50mm on the road.
 
  • If the squish clearance is tighter than 1mm then an extra gasket or thicker gasket is required or a head may need machining a bit
  • If the gap is excessive of 1.50mm then thinner or no gaskets are required.
     
If for some reason you can not get the correct clearance with no gaskets then in extreme circumstances the cylinder can be machined, to bring down the gap, this is very common on GT cylinders, SR cylinders and V3$p@ P200 cylinders. Long stroke engines may have the cylinder head recessed 1.00 - 1.50mm to allow for the piston sticking out at TDC which is normal with 60 - 62mm crank kits.

It sounds like a lot of messing about doing all this but in the long run it is well worth it. When you have finalised what combination you require then it is time to rebuild for the last time. If you are stripping a long run engine and the squish has been set up before it's always worth checking the squish clearance. As an example a decent 200 can be set up with a 0.5mm head gasket this has been standardised for years, but today 200 head gaskets are more like 0.70mm therefore gaining 0.20mm. Similarly with the same engine, have an over sized rebore and the squish alters.

That's how to set the squish clearance but it's not just a case of adding or removing gaskets. Removing a base gasket will lower the transfer and exhaust timing and increase the inlet timing. Adding a thicker base will do the opposite, using a crank with a 107mm con rod totally restricts what you can do, there is no movement, using a 110mm rod is great you have so much to play with on the base packer and head gaskets.

Engine casings vary in heights from manufacturers especially Spanish and Indian casings which can be 1.00 - 1.50mm different, using a 107mm con rod limits what you can do. Fit a TS1 or RB to a high casing and the transfer and exhaust timings will be so high the cylinder will be more like a race cylinder. Set up like this the chances are you have to fit it with no base or head gasket. This is why we used to machine 0.5 - 1.00mm off the base to lower the timings to make a better running engine. Today the 110mm rod is so common, I'm glad because we invented the rod conversions in the 80's and this totally opens up adjusting a cylinder for the better. A well set up and very common way to set a TS1 is to use a fat 1.50mm head gasket this sets the port timings perfect as the cylinder is lowered, the fat head gasket is very reliable and on most casings it will give 1.00 - 1.20mm squish clearance. A good 200 Italian casing with an Italian 200 cylinder would normally use a standard base gasket and a standard 0.5mm head gasket with the head machined the MB way the squish would be fine. Have a casing only 0.5mm taller means you need to ideally remove the base gasket which should be 0.5mm and the cylinder will be set up the same.

Ideally you need to set up the squish based on the port timings, transfer timings are very important to how an engine works so there are some standards which need looking at but we are now getting complicated. For example to make a good TS1 set the cylinder up so the bottom of the transfer ports are level with the piston at Bottom Dead Center when bolted down tight. This is where machining the base of the barrel comes into it, or tweak the cylinder height with different cylinder packers using a 110mm rod, this works for a 58 and 60mm stroke cranks. Then you need to fit whatever head gasket is required or not as the case may be. It's the same with our RT kits, set the transfers level at BDC the kit works great then get the squish right with either no head gasket or with one.

In the end it's well worth doing these jobs correctly, yes they take time, yes they can be complicated, these are every day jobs for us and yes we have to charge for the time involved.  

Mark Broadhurst MD MB (Serious Outdoors Ltd) updated April 2012   ask Mark mark@mbseriousoutdoors.co.uk 

© Copyright 2017 MB Scooters Ltd  |  Terms & Conditions
MB Scooters Ltd - Pitman Road, Denaby Main Industrial Estate, Denaby Main, Doncaster, South Yorkshire, DN12 4LJ, United Kingdom Tel. 01709 869 756 (International +44 1709 869 756) Fax. 01709 860 576 (International +44 1709 860 576)

Share this post


Link to post
Share on other sites

 Now back to piston to cylider side clearnce...

Some people go on and on about having professional machinists oversize the cylinders to the piston that they put in. I've only found one person that I trust with this work locally. And he makes sure that the piston and cylinder clearance is exactly what I asked for. Some machine shops  get your measurements, but they refuse to listen and oversize the cylinder to their own specifications. If you have a sticky manual this topic is covered well in the book. 

Share this post


Link to post
Share on other sites

Thanks for all of this  because I have honestly been disappointed with what is reputed to be such a great machine ever since I finished it. I will do a leak-down and pull the head and check these things.

Share this post


Link to post
Share on other sites
12 hours ago, moto64 said:

Thanks for all of this  because I have honestly been disappointed with what is reputed to be such a great machine ever since I finished it. I will do a leak-down and pull the head and check these things.

The TV200 is a disappointing motor. It's over geared and under tuned. If you look at the SX200 and the GP200 motors Innocenti corrected those issues. 

 

To to get back to your 90psi problem. The compression will go up a little bit but no where near 112psi. I wouldn't bother with a leak down test for two reasons, 1 it's running and 2 you didn't say it was leaking. The low PSI is due to too thick of a headgasket/base gasket or you didn't do the test correctly (WOT carb and kick until the needle stops moving, about 5-10 kicks usually). 

 

When you rebuilt the top end did did you use the thick SX head gasket or the thin TV head gasket?

 

Thats my 2€

Share this post


Link to post
Share on other sites

Thanks, Mike. It is interesting that you say that and it is just how I feel. This was Innocenti's answer to the 200 cc V****'s ?  And the vibration ??? I built my first Briggs and Stratton motor in 1963 when I was 12 and I have a pretty good handle on what's what. I have done full ground up restorations on many cars and do everything but the machine work and upholstery  myself.  My two V*'s are a absolutely wonderful to ride and an Li 125 I had briefly was very smooth ( but underpowered).

This was a bone stock bike out of a barn after 30 years and I added no performance parts. Whatever they built in 63 is what is there and I closely followed Sticky's book for the resto. I got the rings and gasket from Dave at Scooter Mercato and used what he gave me.  He sent me two and I get  .019" on the one I have left. Maybe I should just delete the gasket ? I have been using the same guy for years to do boring, etc. and he does what I ask him. There is no indication of any air or oil leaks. I just lightly honed the cylinder and re-ringed the piston because it seemed so low on compression and I had a slight soft seize last summer ( the two screws on the carb top worked loose) that actually had no apparent effect on how it ran. At 8:1 compression, (8X14 = 112) why wouldn't I expect something more than what I consider a minimum of 90 ? How could the squish be anything other than what Innocenti designed on a stock motor ? I am not a purist and I really am not concerned with the value of the TV200 if it's not fun to ride and I got it for free. If I could make this bike more satisfying by using a different gear set or top end I'll do it. I'd keep all the original parts in case I decided to let it go and someone else was so enamored with owning a stock TV.

Share this post


Link to post
Share on other sites

Different deck heights in the manufacturing of the cases, different sized base and head gaskets, different height of the cylinder, and different cylinder head heights all can combine to make too large of a squish. 

Once you know your squish is okay, the next step is measuring port timings. The port timings literally control your engines power, so measuring these is a critical and often overlooked measurement. 

Share this post


Link to post
Share on other sites

Thanks. I am open-minded and I will look into all of these and report what I find.

  • Upvote 1

Share this post


Link to post
Share on other sites

 

10 hours ago, moto64 said:

Thanks, Mike. It is interesting that you say that and it is just how I feel. This was Innocenti's answer to the 200 cc V****'s ?  And the vibration ??? I built my first Briggs and Stratton motor in 1963 when I was 12 and I have a pretty good handle on what's what. I have done full ground up restorations on many cars and do everything but the machine work and upholstery  myself.  My two V*'s are a absolutely wonderful to ride and an Li 125 I had briefly was very smooth ( but underpowered).

This was a bone stock bike out of a barn after 30 years and I added no performance parts. Whatever they built in 63 is what is there and I closely followed Sticky's book for the resto. I got the rings and gasket from Dave at Scooter Mercato and used what he gave me.  He sent me two and I get  .019" on the one I have left. Maybe I should just delete the gasket ? I have been using the same guy for years to do boring, etc. and he does what I ask him. There is no indication of any air or oil leaks. I just lightly honed the cylinder and re-ringed the piston because it seemed so low on compression and I had a slight soft seize last summer ( the two screws on the carb top worked loose) that actually had no apparent effect on how it ran. At 8:1 compression, (8X14 = 112) why wouldn't I expect something more than what I consider a minimum of 90 ? How could the squish be anything other than what Innocenti designed on a stock motor ? I am not a purist and I really am not concerned with the value of the TV200 if it's not fun to ride and I got it for free. If I could make this bike more satisfying by using a different gear set or top end I'll do it. I'd keep all the original parts in case I decided to let it go and someone else was so enamored with owning a stock TV.

There is a lot of small tuning you can do to make your TV200 perform like it should and actually be enjoyable to ride.

Blueprinting the motor (making sure all the ports match up nice and flow correctly).

Changing the gearing to TV175/SX200

De-restricted exhaust

De-restrict the air box

Electronic ignition (rev out farther).

Skim the head to raise the compression. 

Basically look at the GP/DL motor and aim that way.

  • Upvote 1

Share this post


Link to post
Share on other sites

Interesting: I fed a length of 2.3mm solder down through the plug hole and no matter where I stick it I can't get it squished. I even fed a couple of inches in there and  zip. I assume (?) that there is no flat around the edge from looking at the pics in Stickys and from what I have read the dome of the piston should somewhat match the curve of the head recess. Would the squish be measured at any particular spot or area ? Claiming a shot memory, I just had this apart and can't remember what the top of the piston looked like. The gaskets came from Gene and state "thin type" for the head. The base was paper. I also read that the later SX heads were better (?). So, the head will come off and I'll see what I can see. I can't find the order sheet for the piston but it was from one of the reputable guys and I ordered the 66.4mm one for this motor. Maybe wrong ? I had the crank done by HR Al and I assume (?) the con rod is original and correct. Still flummoxed.

  • Upvote 1

Share this post


Link to post
Share on other sites

Having never ridden a TV200, I can only speak from what others have said about the gearbox being way to tall to be of any use. 

Having just ridden a bone stock Jet200, I can say over and over what a fantastic gearbox the TV/SX/Jet box is.

If you get your squish set and blue print everything and are still disappointed, I say follow Mike's lead and source a better gearbox.

Also Adam Bower at Sole Power Scooters in Pennsylvania can blue print everything for you if you don't want to do it yourself. 

Share this post


Link to post
Share on other sites
On 8/14/2017 at 11:13 PM, theageofindustry said:

Having never ridden a TV200, I can only speak from what others have said about the gearbox being way to tall to be of any use. 

 

Yeah, maybe if I lived in the Midwest. Around here I rarely get out of 3rd. But then again, this thing just ain't running right so I am not in any position to judge

Share this post


Link to post
Share on other sites

OK here's what I got. I can fit an .005" feeler in there which I know is more than Sticky's .003". I did give the cylinder a very light  hone to clean off the glaze when I recently put the new rings in which I gapped at .2mm.  With NO  head gasket installed, the solder squishes to approx 1.6mm at the edge but it tapers quickly ( after about 8mm) off the solder which is twisted to about 4.3mm. Obviously the head and the piston crown are not concentric. Pic shows piston at TDC with cylinder tightened against paper base gasket. I think I can live with the slightly loose piston but what about the squish ?

DSC02755.JPG

DSC02754.JPG

DSC02758.JPG

DSC02760.JPG

DSC02761.JPG

Share this post


Link to post
Share on other sites

The more I look at this head the less it looks like the one pictured in Sticky's book. Like the slope of the perimeter squish area is too steep and soft. What do you think ?

Share this post


Link to post
Share on other sites

The early TV heads were centered. Mine's '63. I am going to get a new head ( http://jet200.com/catalog/product_info.php?products_id=827 ) and the thin 1.5mm gasket Sticky recommends and I'll  check the squish with that. Is it curious that the piston stops so far below the cylinder surface ? I also see that from the MB literature above I see I could eliminate both gaskets if need . I am hopeful.Thanks.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


×
×
  • Create New...