Port timing comparison for Spree/Iowa/EliteSB50 & 50P

[mousewheels]

Been looking at port timings for Honda Scooters & found something of interest to Spree and SB50 owners.

Honda made slight port changes to "Spree Type" jugs. There are 5 different jugs out there . Helps demonstrate what Honda was doing to bump up speed/power or reduce as needed. Watch carefully what you are buying when replacing that jug! Port timing is not the only difference in restricted models, but often is left out when talking about 'de-restricting' a scooter.

Along with the single speed models, the table shows variator equipped models.



I'd like to add any helpful identification we can dig up. For those with "Spree type" jugs around, can you help by checking the castings for the model code (i.e. "GK8" (Spree)) and any other identification which Honda may have stamped? I'd bet Honda ID'd Iowa Spree jugs and SB50 vs SB50P jugs to keep from having manufacturing mix ups.

P.S. In work is a table by model of what parts are different in restricted models

[scooterwerx]

wow, so this is why my buddys elite lx was always faster than my aero when they were stock! interesting!

[noiseguy]

I've been meaning to create that info in a table for a long time. It would be interesting to get some of the "kits" up there as well. You'd want port widths for that as well.

To make things more confusing, though, I'll submit that I don't think the Spree is actually machined to it's book numbers. Measurements I've done on Spree jugs showed that the ports are actually shorter than the book lists, at least by my calculations.

Port height on a couple of Spree jugs that I measured were 9.5mm, the one '87 Elite jug was 11.5mm (by memory). By book, those two ports should be pretty close. Rerun the timing calulations and by all means check my work; it's been a long time since I looked at these measurements.

One other variation to mention; there is an "A" and "B" version of the Spree jugs. These two variants matched some little variations in the case dimensions. You're supposed to replace an "A" jug with another "A" jugs. As I recall, the "A" jug has an "A" on it, and the "B" version has no marking.

Let me know what measurements / etc you want off the jugs; I've a few on the shelf I can pull numbers from.

[mousewheels]

One other variation to mention; there is an "A" and "B" version of the Spree jugs. These two variants matched some little variations in the case dimensions. You're supposed to replace an "A" jug with another "A" jugs. As I recall, the "A" jug has an "A" on it, and the "B" version has no marking.

I've seen that note in the Service Manual. Parts lists show are also 'A' and 'B' pistons. I think 'A' & 'B' pistons and cyls were a matched set for clearance. Reason being manufacturing precision, cost and yield.

Clearance wise the service manual (Aero 50) piston to cyl clearance is given as 0.035 to 0.050mm. A or B sets fit that range.

-- Partial parts list data showing dimensional differences --
CYLINDER A (0/+0.005)
CYLINDER B (+0.005/+0.010)

PISTON A (-0.040/-0.045)
PISTON B (-0.030/-0.035)

-- rebuild time --
0.25mm and 0.50mm pistons have no 'A' and 'B' variants in the parts list. Assumption is, cyl will be bored/honed for proper fit to the piston at hand.

To make things more confusing, though, I'll submit that I don't think the Spree is actually machined to it's book numbers. Measurements I've done on Spree jugs showed that the ports are actually shorter than the book lists, at least by my calculations.

Port height on a couple of Spree jugs that I measured were 9.5mm, the one '87 Elite jug was 11.5mm (by memory). By book, those two ports should be pretty close. Rerun the timing calulations and by all means check my work; it's been a long time since I looked at these measurements.

Thanks for the info. Will be setting up calcuations to convert crank degrees to piston position.
Currently the only rod I have is a TG50 Gyro, its about 3 inch center/center. Anyone have measurements for other models rod length?

[burnt_toast]

I must say there certainly is a noticeable difference in these jugs.

I now remember how slowly my 85 Spree was compared to an 86 I recently restored. Gonna try see again what another 86 can do.

the 85 topped out at 36mph down the STEEPEST hill, while I recall hearing some folks talkin of almost hitting 40 stock, must be the different porting maybe?

[Arnadanoob]

Excellent work.

[noiseguy]

Oh, and there's more. I just pulled 2 early Elite jugs; I think one is '87 and the other from 88-93 or so. Exhaust port is obviously wider on one of the jugs than the other.

0.25mm and 0.50mm pistons have no 'A' and 'B' variants in the parts list. Assumption is, cyl will be bored/honed for proper fit to the piston at hand.

Thanks for the info. Will be setting up calcuations to convert crank degrees to piston position.
Currently the only rod I have is a TG50 Gyro, its about 3 inch center/center. Anyone have measurements for other models rod length?

OK, that straightens out that in my mind and makes a lot more sense than what I had assumed the tolerance issue was affecting. Sorting for diameter, then.

For the crank angle vs piston position, you can use

rod length = 2 x (stroke)

as an estimate. Once you run the calculator, you'll find it's not that sensitive once you get it in the ballpark.

[Lunytune]

So what does all this say for my 99 SA50P? Your chart doesn't make distinction between SA and S series (restricted) for those years. I pulled exhaust, no restriction. I changed jet from 68 to 78 (needed it anyway, plug was light gray). Haven't checked variator plate yet. Need impact or backup wrench... will resolve next week.

Changing jets seemed to help power some, but top speed still 28. I suspect this scoot came out of Iowa. I know the history, original owner was Illinois, second owner was SE Missouri, both non-mechanical, took scoot to Hondasan. VIN reflect restrictions.

Sidenote on Hondasan, I'm disappointed that they would continue to do tuneup all these years with gray plug without seeing fit to upjet.

[mousewheels]

Catch up -

Scooterwerx - "wow, so this is why my buddys elite lx was always faster than my aero when they were stock! interesting!"
Why Honda chose to differentiate performance between the unrestricted Aero and Elite is amazing. I wonder if they put that into the printed specs?.

burnt_toast - "..I now remember how slowly my 85 Spree was compared to an 86 I recently restored. Gonna try see again what another 86 can do."
Yeah, that should do it! Note to those new to Sprees: 86/87 models also got a domed piston (vs dished), different head and a 10% gear advantage.

Arnadanoob -" Excellent work. "
Thanks!

noiseguy - "Oh, and there's more. I just pulled 2 early Elite jugs; I think one is '87 and the other from 88-93 or so. Exhaust port is obviously wider on one of the jugs than the other."
Just like you said earlier we should be looking at port dimension info. Will add rows to collect the info.

Lunytune - "So what does all this say for my 99 SA50P? "
Happy answer is, you're cyl does not need any changes. Service manual and part number comparisons between SA50/SA50P models supports this. (PM sent)


New - Conversion from port degrees to piston position.
Using the stroke length used in pre -94 Elites covers most all models discussed here. A spreadsheet was created to generate a table of crank angle vs piston position. Output has been verified with a web based calculator.

Assumptions:
Stroke: 37.4mm (1.47 inch)
Rod Length: 3 inches (Measured from TG50 Gyro)


Tables:




Conclusions:

1. Honda made small changes, with results of sufficient value to mfg a unique part.
2. Variants make changes described terms of 'cut port a ring width higher' or raise cyl 0.040" difficult to apply with consistent results. We'd need a clue back to the exact jug. Ideally, we'd document changes by degrees, or knowing stroke/rod length document by vertical position.
3. There are further differences in the restricted/un-restricted models, such as exhaust that probably were a factor in port timing arrived at by Honda.
4. Hopefully the info will help get Iowa jugs modified into a real life