My GY6 170cc Upgrade

DISASSEMBLY

I removed the Floor Mat, Seat, Storage Box, Top Box, Rear Fairings and then the exhaust pipe, leaving the muffler in place. Next I removed the intake fan cover.

TIP: All bolts were put back in place to avoid any getting misplaced.

Removing the Carby was easy, just a matter of clamping off the fuel hose, disconnecting the throttle cable and Auto Choke cable.

The stock CV carby was a 24mm model, even with up-jetting it would be a little under spec'd for the extra cc's.

The Head Cover was held on by 4x 8mm bolts and sealed to the Head with a rubber O-ring around it's seam. The breather hose originally ran to the Air Box but will now join up to a new Oil Catch Can (discussed later).

Next came the Valve Rocker cover - this was held in place by 4x 12mm nuts and was easy to remove.

NOTE: 2x metal dowels were holding the Rocker cover in alignment with the head.

Removing the cover exposed the Cam shaft and allowed the Cam to be lifted and tilted towards the Cam Chain.

After the Head removal, the Piston and Bore were exposed along with the metal Head Gasket.

The metal Head Gasket could easily be prised away from the Bore (but not suitable for re-use). This exposed the lower Cam Chain Runner which was removed by sliding it out of the Chain chamber.



The Bore was then gently pulled away from the engine and the Piston was allowed to slide out completely. The paper Base Gasket tore away as expected.

NOTE: The Bore was aligned to the engine base by 2 metal dowels.



On the left side of the Piston (looking from the front) the Circlip holding the Cotter pin in place was easily removed with a pair of pliers.

The Cotter pin slid out smoothly allowing the Piston to be detached from the Crank Rod.

THE 4 HEAD BOLTS (RODS)

Because of the increased height of the 4 Valve Head, 4 longer bolts were supplied. The originals were removed by double nutting them and turning anti-clockwise. A little blue lock-tight was used to secure the new bolts within the threads of the engine base.

NOTE: 2 of the bolts are slightly longer, they are placed closest to the Cam Chain chamber (same as the originals).

The inner edge of the Bore's collar is slightly tapered which greatly assists with pre-inserting the Piston (now with rings) into the Bore prior to fitting to the engine.

By tilting the piston and inserting at a slight angle to the bore, I found that the 1st 2 rings could slide in with minimum effort. The trick was to allow the gapped end to make contact last so that the pressure would close the gap thus narrowing the ring.

Surprisingly the sandwiched 3 rings slid in without requiring too great an angle. Only a few light taps with the palm of my hand on the Piston base were needed, all the while being careful not to pinch the rings against the Bore's collar.



TIP: Lubricate the rings and the walls of the Bore with a little machine oil.



With the paper gasket lightly coated with Hylomar and allowed to dry for 30mins, I aligned it correctly onto the base of the Bore and then inserted the 2 metal dowels into their groves.

Next came the Cotter pin which required that the Piston had enough sleeve exposed (just a fraction before the base ring is again exposed). The Cotter pin was only slightly inserted, leaving enough room for the Crank Rod to be aligned.

I then slid the completed Bore with Piston down the 4 Bolts/Rods.

LONGER CAM CHAIN

Now with a longer Head, the Cam chain needed replacing. Luckily a longer replacement chain was provided in the kit!

I dreaded the idea of removing and splitting the engine for such a simple upgrade so with a bit of research, I read that the Cam chain can be fitted via a joining link. Unlike traditional chains, there is no obvious joining link but upon closer inspection, there is a brass coloured link that can be forced open with either a small chain breaker or if you're as lucky as I was, a small flat blade screwdriver and a hammer with a good aim ;D

I decided to do this after the Bore was fitted to minimise any debris entering the engine. Using my trusty chain breaker (a large set of bulk cutters), I cut the original chain. Using my alternative chain breaker (flat blade screwdriver & hammer on the bench) I gently split the new chain on the brass link.

After taping the new split chain to the end of the old cut chain (still on the crank), I slowly rotated the flywheel and pulled the new chain through. Untaped them and joined the link back together on the new chain, applying some very nervous pressure with my "chain joining tool" (bulk cutters) until I heard a pop - opened my eyes and all was good

CAM CHAIN ALIGNMENT, TIMING & TENSION

Finding Top Dead Center on the Flywheel was a no brainier, it could be both visualised and felt as the flywheel was turned. It was just at the point that the Piston wanted to drop and where the marker on the Flywheel was between the arrow and the line before the T.



I tilted the Cam shaft into the chamber and turned it until the larger of the 3 holes in the Cam sprocket was at top center. The 2 smaller holes were even with the lip of the head enclosure. When I let go of the Flywheel and allowed the piston to drop very slightly, I turned the sprocket anti-clockwise by 1 tooth and pulled the Cam chain on.

To confirm that I had it right, I advanced the Flywheel by 2 revolutions until I was back to the point just before the Piston was ready to drop (between the arrow and line) and then checked the Cam sprocket. The large hole was top dead centre with the 2 smaller outer holes perfectly in line with the lip.

Time to place the Rocker cover on. I inserted the 2 metal dowels and also squeezed a seal of high temperature gasket compound around the lower right bolt. After centering the Cam shaft sprocket within the chamber and aligning it's bearings onto the Head, I slid on the Rocker cover.

3 of the 12mm nuts with washers (top left & right + bottom left) were hand tightened whilst I rolled on the rubber O-ring to the lower right bolt and coated it in a little high temperature gasket compound then also placed on a washer and tightened the 12mm nut over it.

The 2 8mm side bolts (outside of the Cam chain chamber) were tightened and then the head nuts tightened in a diagonal order.



After applying a little Hylomar to the Cam Chain Tensioner's Gasket and letting it set for 30mins, I unscrewed the top screw from it and inserted a small flat blade screw driver. Turning clockwise until it's shaft had completely raised and then inserted it into the Bore - tightened it's 2 8mm bolts before releasing the flat blade screwdriver to let the tension take hold.



Finally capping off the Cam Chain Tensioner with it's centre screw to avoid compression loss and oil leaks.

NOTE: Without first raising the tensioner shaft, damage can occur to the Cam chain and Guide from too much tension.

OIL CATCH CAN

After re-installing a new Exhaust Gasket, Exhaust Pipe, Plastic Engine Covers & Carby, it was time to address where the head cover oil vent would lead to, especially now that the I eliminated the Air Box that the original Head cover was vented to.



Introducing my new Oil Catch Can, with it's poor English stickers proclaiming "High Accelerative" amongst it's many attributes ;D



Attached by Cable Ties to the frame where the Air Box once was, the Head vents to the Oil Catch Can's base via 1/4" fuel hose. From there, the Oil Catch Can has an overflow hose that I cable tied to hang below the bottom fairing in front of the engine bay. A 3rd hose runs from the Catch Can and replaces the Dip Stick so that it can return oil vapour back to the Sump.



The whole unit fits nicely behind the front plastic fairing near the riders feet and can be accessed when the seat is raised.

UNIFILTER

The UniFilter I chose was 100mm long with a 38mm intake diameter and a 45 degree angle cut in red foam.



It comes pre-oiled and is an ideal solution because it's extremely unrestricted compaired to the stock air box and fits snugly between the frame and rear mud guard.



It sits at a perfect angle for visibility too!

CONCLUSION

It sounded nice and smooth starting her up and a little meaner when the throttle was cracked open!

To properly seat the rings, I went with a medium to hard run in.

Briefly:
5min run at 40-60% revs, then a 15min cool down.
10min run at 60-80% revs, then a 15min cool down.
15min run at 70-90% revs, then a 1 hour cool down.

Each time checking for oil leaks during cool down and happy to report she's bone dry ;D

After this run in, I did a top speed check. Prior to the upgrade, I was maxing out at 88kph (54mph) and that was after I upgraded the Belt to a Gates PowerLink 835 20 and matched the 60grams of mixed rollers I had with 6x 10 gram rollers (same total, smoother delivery).

Without pushing too hard before run-in is complete, I can now max her out on a quarter mile straight (level ground) at 95kph (59mph)!

That gives me more than enough headroom in an 80kph (49mph) zone to get me out of a mess and I suspect that after run-in, it will improve even a little more

There are still 2 more performance components I'm keen to utilise, a race mapped no rev limit CDI and a performance exhaust - I'll keep you posted!

Thanks Earl, I always love reading your posts too and have learnt a lot form you

The weather's finally cleared (had 20 days of rain this month), nice blue sky today so time for a nice afternoon ride ;D

Cheers
Ed.

Awesome posts! I really learned a lot from them. By the way, how much did it cost you to do everything you did to the scooter from when you got it bone stock in the box?

Hi Sin,

Absolutely incredible thread! The time and effort you put in with all the pictures thru-out the process, clarity of pictures and description is top notch! You are quite the teacher and wanted to say THANK YOU! By the way, what size are the grips? I have been wanting to change my grips for quite some time now, and I love the Harley type ones you have installed. I am just not sure what size mine are. Thanks again.

Hi Schoei1,

Thanks so much for the compliment, the grips I got were made by Kuryakyn. They're called ISO grips and can be seen here. The model was 6241 (not shown on that page) but fits my scooters' 7/8" bars nicely.