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Old 06-18-2019, 10:53 PM
  #2294  
cathurga
 
Join Date: Jan 2007
Location: Dubai, UNITED ARAB EMIRATES
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Its not so much a common fault, its just that Saito thought that converting engines designed for glow, is as simple as adding an ignition system, and changing the carb, and hey presto! New line of gas engines.. It is not impossible that it could work, as many people are doing the conversion of glow engines by getting new carbs, ignition systems and doing it successfully. The biggest differences being that they need to have a higer than normal fuelil ratio than gas engines normally have. In most cases, this is 20:1 as opposed to 2T engines that are running 30:1, 40:1 and in some cases, successfully on 50:1. The reason is that there is no lubrication APART from what blows by the piston rings. In theory, there is nothing wrong with this, and it seems to work in many cases BUT it also means that many engines are getting a lot of carbon build up on the valves (exhaust mainly) and in the combustion chamber. The engines are NOT able to burn off all the oil as they NEED excess oil to blow by. Problem is, most of these oils are going past the HOT exhaust, and sticking to it, causing build up.
I have been looking into some 4T engines that have been designed from the ground up, as gas engines. One of them is the NGH range. The NGH38 is an interesting one, it has a series of breather pipes from the backplate to the carb and inlet manifold. They seem to be using crankcase pressure to run the carb, and distribute oil/vapour. They seem to run well and apart from a few cases of badly worn cam lobes, they seem to have operated well. Some have even admitted that they 'may' have underpropped/over-revved them which has caused valve bounce and the resulting cam wear.....NGH suggest 32:1 oil ratio for these engines.
The UMS gas radials are ALL using the crankcase to distribute fuel air mix, and they are all specified at around 30:1. They are fairly new, and not many people run them, so longevity is questionable. I know nothing about quality of materials in these, but they look great, and they have a nice range of sizes too, this will be my next radial.
The OS GF40 single gas 4T has a PCV valve type set-up that is what is regulating their lubrication, and is using crafty methods of getting the oil around the engine, and apart from one or two cases of excessive valve train wear, they seem to be good engines. The ones that have had wear problems on the rocker shafts, have cured this by avoiding over-revving. Apparently the PCV valve (ball and spring thing) was not able to open/close properly at high reves, and lubrication ability went down....result: engine wear and failure.
Saito have their radials, and they also have the single gassers (I have the FG40). The singles, like the radials, DO NOT have any method of lube APART from blow by and ALL of them require 20:1 oil. The singles do not appear to have the failure rate, and seem to be quite reliable.....and here is the kicker in my opinion... The singles are all timed around 28-30Deg BTDC....the radials at 44 Deg BTDC.....WHY?......WHY? ....WHY? The ignitions ALL run the same curve..... my guess is that they are constantly trying to appease the masses that demand MORE POWER, MORE POWER, MORE POWER.....theyre getting it, but they are also getting failures.
  • UMS engines, timed at 30DegBTDC, with crankcase lube @30:1 oil ratio
  • NGH engines, cranklube through breathers @30:1 oil ratio. Strangely, they time this at 40Deg BTDC from factory, but everyone running them has changed this to around 30-35Deg BTDC and they run better.
  • OS engines,crankcase lube through PCV setup, timed at 30DegBTDC @30:1 ratio
  • Saito Singles, timed at 30DegBTDC, blowby lube @20:1
  • Saito Radials, timed at 44Deg BTDC, blowby lube @ 20:1
  • FrankenSaito, timed at 30Deg BTDC, crankcase distribution lube @ 30:1

I have not looked at the Valach Engines, Kolm Engines, Laser, Roto or Moki Singles but from what I can see on their pics, all of them seem to employ either a breather pipe setup such as the NGH setup, or they are connected to the inlet somehow. I dont want to speculate on their engines, but it seems to add up to me, that lubrication is a problem, ignition timing is a problem on the Saito's. Over-revving is also going to contribute, especially if its timed wrong, and badly lubed.....although even if those to conditions are met adequately, I would not want to run the revs too high anyway....

All speculation, but it seems to add up. Some people cannot believe that the awesome people at Saito would make such a glaring error, and will stand by the expertise of Saito. I understand this and hope your engines last....