We’ve written a few posts in the past regarding the Suzuki RG500 and the recent price increase around the classic two stroke machines from Suzuki. The RG400 was the Japanese market version created to comply with the 400cc taxation laws which made machines over 400cc very expensive for motorcyclists.

The RG400 used to be a much cheaper way to get the RG500 experience, however the 400cc versions are now starting to command similar value, especially the Walter Wolf and Skoal Bandit liveried versions. The 400cc sibling will provide 80% of thrills compared to the full fat 500cc bike, and visually look identical to each other unless you have them stood side by side.

Differences between the RG400 and RG500

Whilst many may think of buying an RG400 and simply fitting a set of RG500 barrels and pistons will give you a RG500, there are a few more differences to consider. Credit to teamheronsuzuki blogpost where I found some useful information for this post.

1. Carb slide needle and main jetting: 400 = #135 , 500 = #120.

2. Clutch: the 400 has some friction disks less (1 or 2, I’m not sure). See if your clutch will work OK so you may leave it as it is.

3. External sprockets and chain, 400 = 15 front /41 rear, 525 chain, 500 = 16/40, 530.

4. 400 pipes have only thiner stingers, all the bodies are the same.

5. Cylinder, piston: 400= 50mm 500=56mm 400 has 5 intake ports, 500 has 7 intake ports but smaller (but 400′s port in total I think give better flow – i.e. less divided area). External lower sleeve diameter 400=60mm , 500=66mm you need to rebore the upper crankcase. But I’m not sure if you can rebore your 400 cylinder sleeves to reach 56mm so you won’t need any crankcase machining (and won’t need to buy a 500 cylinder set). Remember the 400′s cylinders may give a better intake port flow.

6. Heads diameter accordingly are of: 400=50mm , 500=56mm.

7. Conrods are the same, only its lower bearing consists of some more (1 or 2, I’m not sure) needles so they are closer each other. You may not bother splitting your cases and keep your 400′s bearings though if you go around the stock 500 horse power (no much more).

8. Some small difference in the front brake rotors. 400′s are no “floating” type.

9. The rotary valves have different base, the 400′s is thinner and lighter so keep your 400.

Buying a Suzuki RG400

Finding an original unmolested example is becoming difficult due to the low numbers sold for Japanese market, when compared to the global market 500cc version. One saving grace is Japan’s very strict approach to modification of vehicles which could see a motorbike not being allowed for use on a road. If a bike is a fresh import direct from Japan you’ll have a higher likelihood of a good standard bike when compared to something that has been a ‘grey import’ for many years within a non-Japanese market.

If you have previously played around with two stroke engines you’ll probably be familiar with the main layout of the engine, however setting up a four cylinder 2 stroke engine can be fiddly at times. Seeking out advice from owners clubs and specialists is always advised, especially if you are undertaking an extensive rebuild project involving the engine. You will also need to consider the impact of modern fuels on the engine as part of the rebuild, and possibly consider upgrade where possible to avoid the effects of E10 fuel on rubber and metal parts.

Our recent article on E10 fuels will provide you with some background information that you could find useful.

Happy bidding

This 1985 example has some rough edges but could be a great base for a restoration project, and represents great value as these bikes will only increase in value over the years. For bodywork items like indicators and mirrors you shouldn’t have an issue sourcing these parts which are common across a few models.

Please keep us updated on your plans for the bike if you bid and win, seeing these bikes back out on the road for future generations to enjoy is very important. You can keep in contact by clicking the social media links at the bottom of the page.

Ride safe,

Al (barnfindmotorcycle.com)


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