[AEK]

Hello,

Got this engine and the only markings on it is the "serial# and 499cc".
I searched online and it seems to be a Yamaha and the closest looking match is the sr500
Except none of them have the red circled area shown in the picture.
Would anyone know more about this engine.

Thanks

Aek

 

[Emit R Detsaw]

It is indeed a '78-'81 Yamaha SR500. The "2J2" stamping before the serial number gives it away. Interesting aftermarket carb mount and CC breather. Cannot help you on the red circled area, though.

 

[AEK]

Got a closer look at it and it seems to be a homemade modification, it's a mini spark plug on the side of the head. No idea what it does.

 

[jackattack]

Got a closer look at it and it seems to be a homemade modification, it's a mini spark plug on the side of the head. No idea what it does.

That is really weird. Did you ask the person you bought the engine from what it is? Why would you want a spark plug in a cylinder head? Maybe some sort of sensor is supposed to go in there?

 

[Tonnystark]

the CC breather (the paper plug off) is just to the left of that round stack with the brass 90 off it..normally that is an oil return mounting having a 3/8th inside diameter line on it as the sr is dry sump..
Thinking the plug in the head is a thermo sensor used in conjuction to the carb mount mod. and is a possible early experiment in fuel injection??
(they are now using F.I. on the sr400)
just where did this come from ? ...japan ??

the kick indicator has also been removed ..

 

[TrialsRider]

?:I maybe it's somebody's experiment with alternative fuels. Could run on used french fry cooking oil, or maybe even pig farts.

 

[44dwarf]

My guess is it was used for a compression relief. Phhhhhhhhhhhhh when pulled at speed to dive in to a corner.

 

[44dwarf]

Note the clear window at the cam was replaced with a alum plug. The window was there to tell you when start to kick it thru.

 

[hillsy]

Note the clear window at the cam was replaced with a alum plug. The window was there to tell you when start to kick it thru.

That window was kinda pointless after you'd started the bike a few times. Plus they were prone to leak oil there.

I never looked at mine - just went by feel at the kicker.

 

[hillsy]

Got a closer look at it and it seems to be a homemade modification, it's a mini spark plug on the side of the head. No idea what it does.

My guess is that it was someone's attempt to twin plug the head - quite a common mod for 2 valve combustion chambers as you can't get a plug in the centre the same way you can with a 4 valve chamber.

 

[44dwarf]

That window was kinda pointless after you'd started the bike a few times. Plus they were prone to leak oil there.

I never looked at mine - just went by feel at the kicker.

I almost post that info too.

 

[AEK]

Long story short... I have on hand almost 40k worth of parts half new and half used mostly Harley parts, misc parts, exhausts, tanks, forks, seats, etc... including x2 evo96, extended fat boy frame, sr500 engine. Took 3 days to do inventory. That sr500 engine was off some racing crude cafe bike found the rest of it in other containers in pieces had custom homemade aluminum gas tank with boost gauges, Also has a small lever next to the brake lever, not sure what that is for. Almost every part was custom machined. Unfortunately there was no frame for it. The funny thing is Even though i have all these parts, it's not exactly the parts I need to build my cafe. Now in search of a xs650 or cb750.

 

[Cyorg]

Long story short... I have on hand almost 40k worth of parts half new and half used mostly Harley parts, misc parts, exhausts, tanks, forks, seats, etc... including x2 evo96, extended fat boy frame, sr500 engine. Took 3 days to do inventory. That sr500 engine was off some racing crude cafe bike found the rest of it in other containers in pieces had custom homemade aluminum gas tank with boost gauges, Also has a small lever next to the brake lever, not sure what that is for. Almost every part was custom machined. Unfortunately there was no frame for it. The funny thing is Even though i have all these parts, it's not exactly the parts I need to build my cafe. Now in search of a xs650 or cb750.

Small lever next to the brake lever would fit with the decompressor theory...

 

[Witworth]

If the set up in the side of the head has a tiny spark plug thread, someone's done it to allow a twin spark plug head.

An SR that has a twin plug head can run better ignition timing for race purposes, that gives less detonation (pinging).

Daytona in Japan sold a complete big-fin twin-plug "race" cylinder head once. Mega dollars, and no longer available, I believe.

Danger, is my business.

 

[Witworth]

It is indeed a '78-'81 Yamaha SR500. The "2J2" stamping before the serial number gives it away. Interesting aftermarket carb mount and CC breather. Cannot help you on the red circled area, though.

The round machined thing (with two allen screws) in the middle of the cases, is a place for an oil line to an oil tank. The engine breather is at the back of the cases, as per stock.

Danger, is my business.

 

[grandpaul]

Compression release for starting. Not needed as long as you set up the kicker correctly.

Will do nothing for "diving into corners" on a 4-stroke, that only works with 2-strokes.

 

[hillsy]

The SR/XT/TT500's already had a decompression lever to open the exhaust valve for easier starting.

I think it's a home made twin plug head as earlier suggested.