The timing gear problem is usually caused by wear of the teeth on the crank pinion and exhaust cam.....
As the valve spring is being compressed the cam is 'driving it' but as the cam goes over its peak the spring pressure then drives the cam...
At that moment any slack between the gears will be taken up with a very audible 'click' as the cam jumps forward...This generates a lot of rattle when the engine is running...
If you remove the timing cover and turn the engine over slowly with a spanner on the crank nut you hear and see the exhaust cam 'jump'....
Apart from any wear that has taken place over the years I believe the gear sets were selectively assembled (as they are in Harleys), so even with new gears there can be a mismatch...
I usually go through my box of cams etc. trying different combinations until I get a good fit and/or I introduce some new parts into the mix as well...
You'll soon get used to all that mass 'up front'...Fortunatel;y it doesn't make the bike intrinsically unstable and with familiarity you can still get round the corners in style...
Hopefully your gearbox problem will only be one of adjustment...They are notoriously difficult to get right on the bench as they need the inertia of motion for them to function as intended..... Ian
email (option): ian@wright52.plus.com
This is the ceramic coating that I think caused too much heat transfer to the piston. After 2 seizures I stripped it off. I tried to post these photos last night.
Jeff
email (option): jjbandoo@aol.com
With the head and piston coated, how was the heat meant to be dispersed? These parts are designed to get hot and lose heat via the fins.
I knew a bloke who was racing a T140 at Mallory Park in the early 80's. He thought it would be a good idea to drill lots of holes close together on every fin on the engine. To save weight I guess. The heat couldn't get past the holes and the thing overheated and seized. They're air cooled for a reason
email (option): horror@blueyonder.co.uk
The heat (thermal energy) generated by combustion is transferred into rotation of the crank (kinetic energy) as the piston is driven down the bore by the combustion of the gases.
However, the I.C. engine is very inefficient, with much of the combustion heat (energy) lost through the various engine components...
Combustion temperatures reach 2000 degrees C and an aluminium piston for example will melt at around 635 degrees C...Therefore it is necessary that the heat lost into the various components is quickly dispersed to prevent it causing damage...Thus the fins on the barrel and head, cooling effects of the oil, short exhaust ports etc.
A 100% efficient I.C engine which converted all the combustion heat into energy would ,ironically, run completely cold..An impossibility of course...
The thermal coating Jeff applied is intended to retain more of that lost 'heat energy' by reducing heat transfer, thus making the engine more efficient and increasing power output whilst at the same time protecting the component parts exposed to combustion from a destructive exposure to heat...
If this was the cause of the engine siezures is debateable (as opposed to establishing the correct piston clearance in a non standard engine)...
If the coating was working to contain more heat within the combustion chamber then it would seem logical to suppose that it was also protecting the piston crown from excessive exposure...
The possible flaw in that thinking is that Jeff used a 'pop up' piston arrangement and it wouldn't be possible to coat the side of the piston above the rings yet still maintain the correct skirt clearance without first reducing the piston diameter above the rings to account for the thickness of the thermal coating.....Ian
email (option): ian@wright52.plus.com
Ian,
Here's the autopsy photo of the first seizure:
I did apply ceramic insulation to the raised crown of the pop-up pistons. It did not contact the barrel when running. This first piston had Cerakote MICRO-SLICK applied to the skirt, which I presumed to be the cause of the seizure.
http://www.cerakotehightemp.com/finishes/C-110HQ/micro-slick-dry-film-ceramic-coating/
Subsequent pistons had the thermal barrier Cerakote PISTON COAT applied to the crowns above the top ring but no MICRO-SLICK.
http://www.cerakotehightemp.com/finishes/V-136Q/piston-coat-oven-cure/
This first seizure occurred within 5 miles of gentle running on a cool day. The piston had contacted the slightly-protruding timing plug and looked a little too close to the head on the nearside (top photo), so I used a thicker solid-copper head gasket for .005" more clearance and had the bore honed to .004" clearance for piston #2.
This time I ran it very cautiously, but it seized again within 6 miles. My heart sank.
I asked a trusted friend, an experienced engineer who was Bultaco's US service rep, what to do next. He precision-honed the bore on his Sunnen hone to .0045 and I installed my last 90mm pop-up piston with TOTAL SEAL gapless rings. I measured the compression ratio with thinned oil to be 7.2:1, so I removed the barrel, ground out the PISTON COAT from the deck of the barrel and the head and opened up the flow path in the head and deck to bring CR down to just below 7:1. I left the thermal barrier on the valves, intake and ex ports, and piston crown only.
On Saturday it ran for 16 miles in second and third gear, up to 30mph, with no problems.
I did use Cerakote Arctic Black P-202 heat-dissipating coating for the outside of the head, barrel and exhaust, and INSULCOAT W209 inside the pipe and silencer. So far I can say they look good, are easy to apply, but easily scratched. Further evaluation on these products after more use.
This whole episode left me feeling "too cleaver by half," as my ex would say. Never doing it the easy way. If I had more patience and an unlimited supply of JE pistons I would have altered one variable at a time to better identify the mis-step. But there you have it. Make of this what you will.
Jeff
email (option): jjbandoo@aol.com
It's frequently difficult to identify the exact causes of these problems in very non standard engines...in fact it's not always obvious even in a standard unit...
It's one of the pitfalls of exploring the limits and capabilities of these engines..
I've been down a similarly expensive and depressing path a number of times in the early stages of 'new' engine formats as I've tried to get everything to work according to the plan...
However, I'm sure many others have been more depressed and blown a lot more money than I have...!
As a friend once said to me...'It cost you to learn'....Ian
email (option): ian@wright52.plus.com