Engine Swap - Yam DT into a RCR.

mhr1972 · L Plate Warrior Joined: 03 Mar 2016 Karma :

I'm new here, so i thank inadvance any advice. Trying a motorcycle project this winter of putting a Yam DT 125 lc engine into a Gilera RCR 50 frame. The engines in all lined up, new mounts ect... but it sits slightly higher in the frame and the plug & cap stops the plastic fuel tank from fitting correctly. From research modifying the plastic tank, by an inch indentation is problematic therefore looking at shorter spakpluges. It has a NGK B8ES but could i swap it for something shorter? I know i need a 2 stroke plug, but could i use a lawn mower plug or similar? I would somebody know a shorter plug for another 125 motorbike out there already. Cheers.

stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

If the engine has to sit that high with no option, then modding the fuel tank or fabricating a fuel cell to sit under a cut out tank will be the only proper way to solve the problem.

How much clearance do you need? Is it the plug or the cap that's fouling the tank at the moment? Pics would help.

Using a shorter non recommended grade plug in a performance 2stroke engine isn't going to end well.

If nothing else could be done then modifying the head or having a new head machined up with an angled plug location could work, but offset plugs are not perfect, though if the head is designed for one they work, RGV250 for example

Ariel Badger · Super Spammer Joined: 02 Dec 2006 Karma :

Get rid of the plug cap and go old school.
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talkToTheHat · World Chat Champion Joined: 21 Feb 2012 Karma :

You can get very short 90 degree plug caps. Rubber racing ones can be quite diddy.

You wont find a plug that is shorter outside of the engine. Short or long plugs is in regard to how long the threaded portion is. Most modern lawnmowers are 4 stroke. As the local bod who seems to know what an engine looks like, i spend far too long rescuing lawnmowers that have been fed 2 stoke premix oil despite saying on the filler cap they want 10w40 API SG or similar.

Run the correct plug in a DT or you will have a world of hurt.
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mhr1972 · L Plate Warrior Joined: 03 Mar 2016 Karma :

Thank you all for the replies. I only need 1/2 -3/4 an inch. When i adjusted the frame, cut 'n' welded in new mounts i did not have the spark plug fitted. But the engine is as low as it can go without completly cutting out the cradle and fabricating a new one. I shall stop hunting for another plug. But, like suggested i feel the standard HT cap could be changed as that is quite bulky. Cheers

Robby · Dirty Old Man Joined: 16 May 2002 Karma :

You need some clearance between the plug cap and the fuel tank. If the two are touching, the vibration will wear them both away quickly. You don't want to wear a hole in your plastic fuel tank.

Have a look at the fuel tank mounts, and find a way of raising the tank.

talkToTheHat · World Chat Champion Joined: 21 Feb 2012 Karma :

Yeah, petrol leaking onto your sparkplug is a recipe for fireballs.
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tunertom · L Plate Warrior Joined: 22 Feb 2016 Karma :

hey mate, a lower profile plug would be br8ecm, but i would suggest using a br9ecm as with an 8 heat range plug youll be likely to blow a hole in the piston if you pin the bike for a long period of time Wink

the br9ecm is a good 2cm shorter than a br9es/br8es but has the same thread etc and will run your engine as normal Very Happy

its exactly what you want

see photo:
https://i.imgur.com/AAf9xnU.jpg

Evil Hans · World Chat Champion Joined: 08 Nov 2015 Karma :

Yep, you want a bantam plug (Nothing to do with the BSA Bantam) - that's what the br9ecm is.
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