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After consultation with a motorcycle mechanic friend of mine, here's the path I went down to vent the crankcase on my Koso 170CC 4V kit. I consider this a must do with a big bore kit - there is a significant amount of pressure to relieve in the crank case. He did not recommend an oil catch can, PCV or tappet/head vent - others may disagree.

Supplies.
NCY Oil Decompression Tube; GY6 - www.cajunmaddogs.com ($13)
1.5 ft of 7/16 ID black fuel line - from local Auto Zone ($4)
K&N 62-1010 Vent Filter - https://www.amazon.com/gp/product/B00029WXPY/ ($20)
Black zip tie

Steps (hopefully you don't need these, but this is a how-to section).
1) Take you oil dip stick and toss it in the trash along with the clear tube and metal end from the GY6 kit.
2) Insert new cap from NCY kit.
3) Black out white lettering on fuel line with magic marker.
4) Insert hose clamp over fuel line, insert fuel line onto new vented cap and clamp tight.
5) Route fuel line up under side panel - either side will work depending on what you already have stuffed up there. I went to the far side to avoid my air intake.
6) Remove side panel.
7) Cut fuel line to desired length - at least 1' long.
8) Insert hose clamp, insert K&N Filter into end and clamp tight.
9) Zip-tie off.
10) Put the side panel on while enjoying a frosty beverage.

Pictures.
Front filter is this one - other one is on the factory crank case breather.

IMG_0651.JPG IMG_0657.JPG IMG_0655.JPG IMG_0656.JPG
 

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I did order two of the same dip stick decompress-or kit like the one you posted since the bigger I/D size is needed for my Finbro 183 engine. I checked the route of the hose and yes you need a fuel line hose since it seems to with stand the engine heat better than the clear plastic hose. I'm still using the PVC valve so as to reduce any air going back into the oil spout hole.

My BrianS 170 engine has Zero issue with oil catcher unit only the Finbro 183 engine that is why I ordered the kit plus I will have a spare kit when I build my Takegawa 181-4v super head kit with the Kitaco crank/rod upgrade.

the price was the same from Steady Garage and also from the Rockshop.com
 

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That's a great way to reduce crankcase pressure- just don't run lean and blow a head gasket or scuff a piston at speed with that setup. Your lower left leg , brand new riding boots/socks, the bike's wiring harness under the tank and the rear tire will be coated with hot slippery oil. Ask me how I know.
 

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I've been running this same setup, just using a uni breather in a different location so that if any oil did drip I'd see it on the engine up front. Haven't lost any oil yet and temps are better than they were. The larger ID hose of the GY6 breather hose is the key to allowing enough ventilation without forcing the oil out too.
 

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That's a great way to reduce crankcase pressure- just don't run lean and blow a head gasket or scuff a piston at speed with that setup. Your lower left leg , brand new riding boots/socks, the bike's wiring harness under the tank and the rear tire will be coated with hot slippery oil. Ask me how I know.
How do you know?

Sent from my Nexus 5X using Tapatalk
 

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ImageUploadedByHondaGrom.net1476875730.840112.jpg
First 204 piston I had. I was trying to get away with fueling with a Finbro ecu/recommended injector. Made such a mess that a catch can installed when new piston went in.

Sorry didn't take pics of the oily mess 😁
 

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Both breathers on same side mock up.


#Aracer rc mini plus 2 #Takegawa 181cc #finbro 125cc head #yoshimura cam #koso 34mm tb #finbro 6 hole injector #brocks exhaust
 

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I recommend running the hose high and around the gas tank and using bigger I/D hose for the original crank case vent and also on the oil spout hole.

Those coming from the oil spout hole is routed straight up and looped than goes thur a filter and after the filter goes to a PVC valve to the front of the grom on the right side.


The original crank case vent hole has a bigger I/D hose which goes up and loops around to the under side of the rear of the gas tank and goes forward with a filter installed and then goes to the OEM modded air box.


Still having problems only with the Finbro 183-2v BBK with heat and it would need a external oil cooler and electric fan for stop and go traffic since I notice the temps would go up to 250F plus. The 170 BBK has limited problems with heat if the grom is moving but it will have heat problems in the summer time.
 
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