NGH 4 stroke petrol mix

[Jon H]

Looking at the photo Paul i dont think lubrication was your problem. There is no heat damage in evidence, bearing surface looks ok from this photo as well and there is no deformation so i do not think it seized due to a lubrication deficiency. If it had, the thing would be badly bent and aluminium pickup would be everywhere. I think Saito rods are forged? Certainly its not machined from solid. In any case, it looks to me like a fatigue failure with a crack probably starting at the oil hole or a notch in the face like we see on the remains of the rod in the photo. 

 

Also while i admire your efforts on the bronze rod it will be extremely heavy compared to the original so you may completely upset the balance of the engine. 

[Rich Griff]

That alloy Conrod looks a bit bent to me, could be my eyes or the picture...

 

It looks quite dirty across the crack by the oil hole and a little rough for half of the bit shown...

 

There is a bit missing...

 

How is the crank pin ?

 

The rod could have got bent when it let go, a mess in the crank case ?

 

Wasted spark ignition system ?

 

With auto advance ?

 

How fast was the motor running when the rod let go ?

 

 

Edited October 5, 2021 by Rich Griff

[john stones 1 - Moderator]

Oil mixes ? Work tools run on 50-1 been doing it a long while, and for the company I worked for it was Stihl mineral oil, never a seized engine, not a one and we've had some right puddings working with us over the years.

 

Are aero engines made of slightly different metals/alloys ? No idea, nor do I care. I run mine on what the warranty tells me, I don't care if I could get more rpm or more power, breaking stuff hurts because moneys tight, so I tend to be cautious.

 

NGH 4 strokes ? Not a champion for them, just relating what I've seen, been two at our club both run by lads who run any engine without many issues, bit crude looking, not the most powerful, but they work for these lads.

[Paul De Tourtoulon]

Engine was running normally, straight and level with an APC 16 x 8 prop on my 2+ metre Stuka, 8.400rpm on the ground,

the engine just stopped and threw the prop, the plug was slightly black and the con rod was more 'bent'

than the picture, I straightened it out a bit to measure it up, it is ( from memory) 13 grams against the original forged one at 8 grams.

[Engine Doctor]

Many purpose built petrol engines a roller bearing big end and little end  that will happily work with minimal lubrication, hence their ability to run on a 50 : 1 mix. Smaller engines with plain or bronze bushed bearings tend to have higher ratios of oil mix for big end / little end lubrication.

Comparing two strokes and four stroke model petrol engines lubriction requirements is not relevant as they both rely on different lubrication system/approach. You cannot  compare glow versions as these have far greater volume of fuel/ oil mix passing through them.

Whereas a two stroke petrol might happily run on 50 : 1 mix you have to remember that every revolution a fresh charge of cool oil/ fuel mix is drawn into the crankcase cooling and lubricating the moving parts.

Now think about the internals of a model four-stroke engine . Many have plain or bronze bushed bearing big and little ends.  They only draw a fresh charge of fuel / oil every second revolution. That charge is only drawn into the cylinder and most of it ,after ignition is expelled as exhaust. The only oil to getting the internsl moving parts is oil that is a fraction of the oil in the mix that is forced past the piston ring by the compression stroke. Hence the requirement of a higher oil / fuel ratio to keep the internals happy.

An occasional  injection of fresh oil into the crank cases ,cam gear and valve gear on four-stroke is essential maintenance .

Some of the higher end four strokes like Moki have roller bearings big end etc ( not sure about little end) and they recommend 50 : 1 mix . 

 

 

[Frank Skilbeck]

The NGH 38cc fourstroke has a roller end big end, also has a connection from the inlet manifold to the crankcase labelled lubrication plus a separate crankcase vent, so portion of the inlet mixture is routed to the crankcase, while the big end is a roller bearing the cams and valves etc all need lubrication too so it's best to stick with the manufacturers recommendations re oil content.

Let us know how you get on with the engine, I find mine very difficult (OK impossible for me) to hand start but fires up very quickly with a starter, choke needed for the first start of the day. They do seem sensitive to the exhaust and putting a slightly restrictive exhaust will loss a few hundred top end rpm.

[Rich Griff]

The channel from the inlet manifold, is it routed from between the carb and cylinder head and does it have a one way valve and restrictor ?

 

Or does the crankcase add as a boost, to the intake charge, on the induction stroke ?

 

So the fuel and lube mist/vapour/gas lubes the engine internals....

 

I can't see any fuel and lube blowby doing much lubrication ?

 

A total loss lube system topped up from time to time, it just chucks out too much lube content via a breather ?

 

Anyone modified a small capacity honda 4 stroke ohc wet sump strimmer motor for aeromodeling ?

 

They may be problematic when inverted for more than a second or 2 with zero gee...

 

Mind you strimmers can get placed/held in some odd positions, for a 2 stroke it is unimportant, clunk tanks...

 

Baffled sump ?

 

I'll go and have a look-see on CMSNL exploded views...

Edited October 6, 2021 by Rich Griff

[Frank Skilbeck]

There you go Rich a video on how the Hondas are lubricated, basically they create an oil mist within the crankcase etc. Looking at the engines compared to dedicated aero engines they look quite bulky and heavy so maybe not ideal for conversion to a model aircraft engine.

 

Getting back to the NGH, the crankcase vent to atmosphere has quite a small hole in it, so that is the restrictor, so on each stroke only a small amount of mixture is expelled that way. Might not be a great way to do the lubrication, but when I went to check the valve clearances on mine there was plenty of oil in the cylinder head.

[Frank Skilbeck]

Was flying at a recent fly in with my NGH 38cc, after a 6 month layup, fired quickly on the starter with the choke on, choke off and it was running away nicely. I was trying the standard straight through exhaust pipe, but to route the exhaust gas around the undercarriage leg I'd put on a piece of silicon pipe, lasted around 10mins before it broke where it slid onto the exhaust pipe. Looks like standard silicon exhaust pipe can't handle the high exhaust temp, so before I make a metal pipe extension, anybody got any alternative suggestions.

 

The NGH BTW ran faultlessly all day.

[Paul De Tourtoulon]

Ni plastic or rubbers with support the heat, I got some of this flexible metal, but it doesn't seem to like the vibrations of my Enya 120 4c,,

[Engine Doctor]

Try speaking to Alan at Weston UK he used to keep PTFE  tube / exhaust joiners.

[Paul De Tourtoulon]

2 hours ago, Engine Doctor said:

Try speaking to Alan at Weston UK he used to keep PTFE  tube / exhaust joiners.

I found that they only worked after an aluminium silencer on Petrol engines.

[Frank Skilbeck]

The exhaust pipe is 14mm OD so I need something for that, the smaller PTFE (Teflon) joiners are around 19mm ID so too big. I was at Morris Mini Motors and they do these but didn't have any small enough.

 

I've found some stainless tubing which is 14mm ID, (1mm wall thickness) so I'll probably buy a section of that and slide it over the exhaust to route the exhaust around the undercarriage, shouldn't be too hard to put a 15-30 Deg bend in this.