Mystery engine? Cylinder spacer, porting.

[yamanube]

Pulled this from a superjet I just bought with no information or history.
Has 61x cylinders, looks like 84mm pistons, roughly 2mm spacer plate under cylinder, porting. Near as I can tell it is stock stroke (best measurement I could get with a caliper depth gauge), cylinder looks to be 117-118mm tall. This is all eyeballed with a cheap caliper and the engine assembled.
Is this an old race mod or something to get the port height up?
I might take the head off and look at porting, or I might put it back in and ride it just wondering if anybody had seen something similar.

 

[waxhead]

4-5mm stroker i would guess

 

[yamanube]

4-5mm stroker i would guess

My crappy caliper really looks to read 68mm stroke. That was my first assumption.

 

[waxhead]

My crappy caliper really looks to read 68mm stroke. That was my first assumption.

it may be but thats a lot of stroke on a stock cylinder it would make stock port timing huge. I think they used to use the 650 cylinder back in the day to make it work

 

[Jr.]

Probably a 73mm stroke or +5mm stroker, that would put it at about 809cc
very common back in the old mod days.
The spacer is probably 1.5 mm with the other 1mm going up into the dome for a pop top.
If its still in good shape? Run it! You will be surprised at overall performance!

 

[MTRHEAD]

First the transfers don't look radical at all from that pic. Looks like stock sleeve just cleaned up a touch - not even ported that much.

If stroke is stock its a way to raise port timing for RPM.

Its not decked enough to be an old flat top superstock motor. Put a pic up of the exhaust port.

 

[waxhead]

What year did the 64v become black case ??

 

[Vortex]

What year did the 64v become black case ??

The black cases that were original to my 03 s.j. are 64v

 

[yamanube]

This engine came out of a '98 but I am unsure if they are original.

 

[Req]

I would measure the cylinder height and compare it to a known 61x. If it has the same amount of material removed off the top of the cylinder that the spacer added then they did it to change the port timing.

Stock port timing
179 exhaust duration, 118 transfer duration, 30.5 blowdown.

Raised cylinder using 2mm spacer and yamabond instead of gaskets (1.5mm lift)
184 exhaust duration, 125 transfer duration, 29.5 blowdown.

I am doing something similar to get my porting spec where I want it to be.

 

[yamanube]

Locked up the engine from water intrusion and neglect. Pulled it apart to find some sort of big bore sleeve. The top of the cylinder definitely appears to be cut approximately the width of the spacer. Port work between the sleeves and castings looks pretty crap. I cant tell if the builder was just throwing parts at this engine or knew what they were doing. Cases are unported.
I will post more pictures this week.

 

[SBrider]

you thinking of selling that cyl. ?

 

[yamanube]

you thinking of selling that cyl. ?

Sure, shoot me a message if you'd be interested.

 

[yamanube]

More fun, if anybody is still following along. The domes are 29cc 701 domes (ADA says roughly 230psi) that was blowing 150 psi on a relatively new topend. I have yet to scrape off the base gasket(s) and remove the spacer but it seems with the spacer, the deck height is slightly taller than stock. I may have been wrong on how much the cylinder was decked (if at all).

 

[Harbor]

So did they lower the compression with that spacer instead of getting bigger domes ?

 

[Req]

Did dude get the wrong domes and then space the cylinder up to lower compression maybe? This whole thing seems like a birds-nest.

Edit: Harbor beat me to it.

 

[yamanube]

The further I get into it, the less sense everything makes. Stay tuned for more detailed photos of the "port" work.

 

[Quinc]

"Hey bro my buddy had this spacer on his jetski engine and it did like 70mph! You want to trade a 12 pack for it?" - How the spacer got there probably.

 

[Storbeck]

If it has really high port timing the measured compression would be lower than what you'd get with stock port timing. That still seems really low though. Possibly custom machined domes and that was just the part number for the dome they started with before machining? Maybe using some oddball piston with taller deck height that requires the spacer and custom dome?

 

[yamanube]

If it has really high port timing the measured compression would be lower than what you'd get with stock port timing. That still seems really low though. Possibly custom machined domes and that was just the part number for the dome they machined?

The deck high is definitely taller than stock with the spacer. As far as I can tell, the crank is stock (I haven't removed it from the cases). I though the domes could have been custom machined from the out of the box ADA 29cc domes but that would only make sense to me if it was set up without the spacer to get the squish right. I quick measured the port timing from the top of the cylinder but now seeing the cylinder is taller than stock, my top down measurements mean very little.