A Royal Enfield forum for the people

[Street_Kleaver]

So it's started. Head is off. As per usual the ports on this thing is very sub-par.

The inlet tract is a bit all over the place. Throttle body starts at 34mm, along the runner down to 32mm at the head entrance and opens back out just before the valve bowl. I'll clean all that up and make it a uniform 34mm.
Unshroud the valves and clean up those recessed edges around the valves.
Upon the head tear down the valves were a bit wiggly in their guides. But this engine has seen 26,000 km/s on all stock internals.
Compression test is still very good and quite high at 175psi. I was going to shorten the barrel. But with our fuels I'll leave it alone, run a thinner base gasket which reduces the cylinder height by 0.8mm and a flat top forged piston.
A lesson learned with my Bullet runs 168psi of compression and it "just" have the detonation under control at the standard base setting with electronic ignition. So I don't want to push it just yet, the GT has no issues with its present compression.

The goal is not to go balls to the wall with this engine. But still strike a good level of performance and reliability as well, much the same as my Bullet. This bike I take on long rides. Generally 500km in a day. So I'm keeping that in mind.
So far on my bench is a full set of new upgraded premium bottom end bearings and Renolds endless chain from Hitchocks. All new seals, gaskets. New standard conrod, which I'll clean up and polish. I'll clean up and polish the rockers.

On the way is Hithcocks 90350 Perfomance Cams and the GT535 90247 Competition Valve kit. Just waiting Hitchcocks to email me back on their Forged piston bore specifications. To see if I can get away with a hone on the standard bore or I have to re-bore with the +10/0.25 oversize piston.

[Ace.cafe]

The UCE can tolerate higher compression than the Bullet if you achieve the squish factor. We have seen as much as 190 psi be okay with the Ace Billet head. Use a 1mm head gasket thickness on a flush( zero deck height) barrel/piston at TDC.

On your porting, don't touch the port floor. Do all the grinding on the roof and walls, effectivy raising the port slightly. This makes a better short turn shape and will help flow. Leave the valve guide boss in the port for support. You can streamline it for flow. Try to match the injector housing to the port entry as well as you can.

On the exhaust port, pretty much similar treatment.eave the D shape on the floor. Don't enlarge, but smooth and even-out the roof and walls. Avoid the temptation to go bigger on the exhaust. We have 34mm exhaust port exit on the billet head working.. with 6500 rpm and 38rwhp. You don't need a big exhaust.

Be real careful with the RTV sealing goop on the timing side cover near the oil pump. Be certain that no sealer gets into the oil passage, occluding the oil flow. This was seen often on factory built UCE engines, so watch for it.

[Street_Kleaver]

The UCE can tolerate higher compression than the Bullet if you achieve the squish factor. We have seen as much as 190 psi be okay with the Ace Billet head. Use a 1mm head gasket thickness on a flush( zero deck height) barrel/piston at TDC.

On your porting, don't touch the port floor. Do all the grinding on the roof and walls, effectivy raising the port slightly. This makes a better short turn shape and will help flow. Leave the valve guide boss in the port for support. You can streamline it for flow. Try to match the injector housing to the port entry as well as you can.

On the exhaust port, pretty much similar treatment.eave the D shape on the floor. Don't enlarge, but smooth and even-out the roof and walls. Avoid the temptation to go bigger on the exhaust. We have 34mm exhaust port exit on the billet head working.. with 6500 rpm and 38rwhp. You don't need a big exhaust.

Be real careful with the RTV sealing goop on the timing side cover near the oil pump. Be certain that no sealer gets into the oil passage, occluding the oil flow. This was seen often on factory built UCE engines, so watch for it.

Cheers mate. I've had a good look at it last night and pretty much what you've mentioned is how I'll attack it. It's mainly a tidy up and port match everything that's already there, mainly focusing just getting the inlet port matched and uniform. But it's no where near as rough as the iron barrel head. Just some ugly casting and the transition into the valve seats is bumpy. The exhaust port is measuring 30-31mm at present.

I've measure the bore and it's at its service limits. So I've ordered the +10 thou oversize omega from HMC. Since I have to send my barrel and crank to be rebuilt at Serco I'll get them to skim some off the base of the barrel housing.

With the standard 1.3mm Base gasket, Top of the piston to the barrel deck height is 1.95mm
Using the 0.5mm base gasket will bring it down to 1.15mm to the barrel deck.
So skimming 1mm off should be safe?
With a 1mm skim and 0.5mm base gasket the piston crown will be 0.15mm lower than barrel deck height.
Depending if the piston crowns are the same Omega vs Standard. Parts should arrive next week.

Will valve reliefs in the piston crown need to be cut with that height and H's cams like on Taurims build?
I'm "trying" to be modest with this build. Haha.
I actually enjoyed it where it was but it's due for a overhaul.

Cheers mate

Ben

[Ace.cafe]

The best performing squish is 1mm from top of piston to flat surface on the head. We typically try to achieve a flush piston crown to top of barrel relationship. This allows easy setting of squish distance by using the thickness of the head gasket, which is normally 1mm thick, unless they have changed it. The squish distance can be larger, BUT its performance reduces as the distace gets larger. It should not be larger than 1.5mm or detonation is actually worsened until the distance becomes more than 2.5mm. That is the danger zone with squish, so it needs to be less than 1.5mm or more than 2.5mm. Do not go smaller than 1mm because there could be a slight potential of clash.
It doesn't matter too much HOW you get the distance, as long as you get it. I would strive for 1mm because that is shown to give the best performance.

Regarding the valve-to-piston clearance at TDC, you will have to check it with a mock build and slow rotation around TDC to see if you get 1.5mm clearance. We typically use a 1.5mm pad of soft clay on the piston, and if you rotate over TDC without getting any dent in the clay, you are good.
I don't use Hitchcock cams, so I can't say if there will be any need for valve reliefs. You will have to do the checking carefully if you suspect they might touch. If you need to cut some relief for the valve, you still want it to yield a 1.5mm clearance to make a safety margin for valve float/lifter pump-up. 2.5m safety margin for the exhaust valve, which typically would not need a relief cut on the piston.

These things typically need at least .005" piston-to-wall clearance with a forged piston. I don't know the growth specs on that piston, or whether it is 2618 or 3034. If in doubt, put it in an oven and warm it up to 300-325F and measure skirt front to back at pin height. Add .001" and that is your bare minimum clearance figure..

[Street_Kleaver]

Sweet. I'll get that machined when the barrel gets sent down at the end of the week. With the 0.5mm base gasket, it needs 1.4mm taken off. Easy done.

Thanks for the porting tips. The intake side isn't that far out of misalignment. Won't take much work at all.
The exhaust port is a bit choked. Especially from the valve seat to the bowl. It really steps in about 2mm. The casting (not the seat) measures 29mm. So there's a bit of room for improvement there.

[Ace.cafe]

Depending on the shape, a narrowing behind the exhaust seat can be good for high exhaust speed during the scavenging event. It also might be just a restriction. It depends. A flow bench would show it.
You could take the exhaust port exit out as far as 33mm or 34mm if you wanted to. Polish it well.

[Street_Kleaver]

So. On with the show.
It's been at this stage for over a week, slowly poking away at it. I've just been a bit slack, sorry!

Crank has been rebuilt by Serco racing here in Qld, Aus. They also did the shortening off the barrel.
Just used a OEM con rod. I have some fellow Aussies who have done similar builds to this one and has racked up 60,000 km's on a OEM crank. So that's good enough for me to continue to use the OEM rod.

The upgrades I did do with the bottom end is replace all the main bearings with Hitchocks "Premium" options. Which are NKE Austrian Bearings. Along with a Renolds primary chain.

Removed the little spring out of the chain tensioner. I have read and been told by a local bloke with a 39 rear wheel Hp GT535 with similar mods has been giving advice that the little spring can over tighten the primary chain causing the main engine sprocket bolt and clutch basket nut to work loose. The bonus is there is a filler bung, pop a screw driver in there and feel the chain tension. Unscrew the M6 cap bolt for the tensioner spring and stick a little pin punch up there and click it up one click on the tensioner ratchet.

Barrel shortened 1.5mm
Polished the fins on the linisher for visual horsepower upgrade.





After a few goes. It's finally back in its home. First attempt I missed the jack shaft for the starter motor gear. 2nd attempt was a keeper dowel pin on the gear select cam shaft. 3rd times a charm. Needless to say, I got quick at it!



Got the deck height pretty well spot on at 1mm. Checked with plasticine. Inlet valve has 1.8mm clearance to the piston crown.



I also removed that hideous silver powder coat from the engine cases. I don't recommend! That stuff is on there to outlast religion. It's bloody hard! But the cases look a lot nicer now. Also polished all the fins on the linisher and side cases.









Just waiting on my chain to arrive so I can ride the thing!

[Street_Kleaver]

I forgot the head!







Inlet and exhaust ports. Just need the little lumps next to the guide casting smoothed out. Did that before it went to the head shop and forgot to take photos
Inlet is a consistent 34mm all the way though. Before it was 32, 30 out to valve bowl.
The basic shape has been kept with the slight kink it has, just smoothed out throughout that transition and not so profound. Floors didn't get touched, just the short radius cleaned up into the valve seat.

Inlet valve unshrouded and all the ugly lips and edges cleaned up. Intake manifold port matched.
Exhaust port ended opened up to 31mm from 29mm.

I hit the ports with a 240grit scotch brite wheel, then a quick buff with a little felt wheel with the Dremel and flex drive. So it still has "hair" but shiny. Kinda of like a milled finish.

Unfortunately I don't have access to a flow bench where I live. Let alone a Dyno now. Local guy has retired and is only doing basic mechanic work out of his workshop at home.

Next port of call for me is 4hrs away.

[Ace.cafe]

Should do what you want. Probably around 36hp at the wheel, all properly tuned. To get up to 38hp, it needs a 36mm throttle body and port, and a 6500 rpm rev limit.

[Street_Kleaver]

I'd be more than happy with mid 30s.

A chap that's been helping has a similar build. Although he got the combustion chamber welded up to a oval shape rather than the D shape with the inlet un-shrouded.

Ported via flow bench, with the same valve kit and Hitchcocks cams but with stock piston/barrel, bottom end and throttle body. Managed to get 38.9Hp and 37.5fLB rear wheel on the dyno.

Unfortunately in my small town I don't have access to a flow bench unless I drive 4hrs. Same with the Dyno when it comes to that!