Glow to Petrol Conversion.

[Doug Ireland]

I bought all the bits from JE yesterday and will try and convert a SC 52FS with them. I also got two new head gaskets to lower the compression a bit. Question is, should I fit both of them or just one?

[Gerry Stansfield]

I didn't use any gaskets on my ASP 52. A.R. as the compresion wasn't that good anyway,But it still runs O.K. It peeks out  at 7500rpm on a 12x6, tickover around 1700.

[Doug Ireland]

I've just a closer look at the engine I want to convert and can see a potential problem. The prop driver has a groove machined around its circumference which will make fitting the 4mm magnet a bit tricky. A normal twist drill would "chatter" in the groove and I don't have access to and End Mill. Would a straight Router Bit work?

 

Forgot to mention, the SC 52FS engine is brand new and never been run.

Edited By Doug Ireland on 15/03/2010 11:57:07

[Brian Parker]

Watching with interest.

A few comments if I may..

Doug, What about a small centre drill to start it off?

Mixture..At ¾ turn out thats not much oil per rev, almost a drought in the crankcase of a conventional 4 stroke.

 Gerry, Are you using synthetic oil or 2-stroke oil in the petrol mix?

 There is probably quite a fine line between insufficient oil for the bearings and an excess of oil clogging the exhaust valve stem if using the 2-stroke oil.

The compression pressure requirements for glow and petrol are quite close and if necessary retarding the ignition slightly for a test run rather than stripping out the engine and adding shim gaskets might be worth a try even on a new engine.

Satisfactory air/fuel(petrol) ratios for the ignition of 4 strokes seem easier to achieve than for a 2 stroke.

While it may be safe to reduce the oil content of a 2 stroke a 4 stroke will need a close eye kept.
Doug, Some before and after results on the new engine would be useful, also any ignition advance/RPM data would come in handy if possible.

[Gerry Stansfield]

Doug,

The propdrive on mine has a groove turned in it. I managed to drill it by holding it in the benchdrill vice, and used a drill size same as magnet minus a couple of thou: pressed the magnet in to just below the surface of the propdriver and then filled the groove in with car body filler then smooth it down, theres no way it's going to come out, {mine hasn't}                  Brian,

Im using 2 stroke oil, at 20 to 1, and there,s a slight residue out of the exhaust, so oil must be getting round.  It's run for about an hour {on and off } up to now and nothings happened yet!!         

[Doug Ireland]

Thanks for that Gerry, I don't have a drill press at home so it will need to wait until I go offshore at the end of the month.

[Doug Ireland]

Got the bits from JE this morning and as I'm an impatient sort of chap I just ordered a pedestal drill from Screwfix; will arrive tomorrow. So with a bit of luck I should be able to run the new engine sooner rather than later

[Gerry Stansfield]

Best of luck Doug, Carn't wait to fly mine, weather seems to be improving, so might get a flight soon, [fingers crossed}.

P.S. Take it easy when drilling hole for magnet!.

[Doug Ireland]

The story so far. Ive marked the position for the magnet at 28 degrees BTC so now its the simple () task of drilling the prop driver.

 

[Steve Hargreaves - Moderator]

Oooo-er Doug I hope that vice isn't done up too tight....... squeezing a crank case in a vice is a really good way to crack it!!!!

[Doug Ireland]

No its just sitting in the open jaws Steve.

 

Drilling the prop driver proved more difficult than I anticipated, considering the deep groove around it. The hole just broke through the prop side of the driver so the magnet will need a little dressing with a dremel.

 

I'm a bit reluctant to strip the engine down (never pulled a four stroke apart before) to drill/tap a couple of m2 holes in the front bearing housing for the Sensor Mount, so I'll need to come up with another way of doing it.

[Steve Hargreaves - Moderator]

I knew you wouldn't let us down Doug !!!

[Martin Harris - Moderator]

Posted by Gerry Stansfield on 15/03/2010 21:55:27:

Doug,

The propdrive on mine has a groove turned in it. I managed to drill it by holding it in the benchdrill vice, and used a drill size same as magnet minus a couple of thou: pressed the magnet in to just below the surface of the propdriver and then filled the groove in with car body filler then smooth it down, theres no way it's going to come out, {mine hasn't}                  Brian,

Im using 2 stroke oil, at 20 to 1, and there,s a slight residue out of the exhaust, so oil must be getting round.  It's run for about an hour {on and off } up to now and nothings happened yet!!         

 Might be worth considering that the groove is there to give purchase for an extractor, assuming it's got a taper fixing - can't remember offhand.  Might be better to leave at least part of it unfilled?

[gerald stansfield]

Martin,

         The trouble with not filling the groove right round would give it chance to fly out at speed maybe??.

 

[Martin Harris - Moderator]

That's always a possibility and something that happened to a clubmate with an engine from one of the major petrol engine manufacturers.

 

You could certainly live with the possibility of having to grind out some of the filler in the event of needing to pull the driver - or take the much less preferred option of driving the shaft through the driver which is an easy way to cause damage. Unfortunately, I doubt that there's a great deal of strength in the filler unless you've used something like P40 with glass strands.

 

If the magnet is even a little below the surface I'd think about staking the ali. around it with a centre punch but would probably have left a little clearance when drilling and Araldited the magnet in.

 

It's just occurred to me that I think I read somewhere that Neodymium or one of the other common magnetic material is nasty stuff if powdered and is nickel plated in order to keep things safe so you might want to look into this before using your Dremel.

 

Added a little later:

I thought I'd check and can't see anything about a safety hazard but if the magnet is of sintered (compressed powder type as per Neodymium and many others) construction, grinding it will remove the plating, allowing rapid corrosion and probably encourage physical failure due to loss of integrity.

 

Edited By Martin Harris on 22/03/2010 22:25:59

 

...and car filler is usually porous so a coat of petrol resistant paint might be a good idea as yours is already done?

Edited By Martin Harris on 22/03/2010 22:33:03

[Doug Ireland]

I'm afraid I made a bit of a hash of it!.

 

Stripped the engine down, drilled and tapped two M3 holes in the front bearing housing and reassembled the engine. So far so good. Mounted the Sensor Housing to the engine and connected the ignition. Then I discovered the sensor is thirty degrees out and there is not enough adjustment in the mounting bracket to make it work. As it is, the plug now fires about five degrees BTC!

 

Rats...

[Brian Parker]

Doug,
Just reposition the magnet (or fit another) on the driver to give the correct timing. Remove the original if fitting a new magnet.

As stated earlier, Neodymium fumes are toxic so take care if drilling the old one out. They are also very brittle.

[Doug Ireland]

Hi Brian,

 

The prop driver looks a bit like a Swiss Cheese just now as my first two attempts saw the drill bit run off into the groove around the hub. Ordered a couple of replacements from JE.

 

Onwards and upwards

[Brian Parker]

Doug,
Start the hole off with a small centre drill (Cronos or RDG tools) guaranteed not to wander if you take it steady and cheaper than a prop driver.
You can also get the magnets from ‘guysmagnets.com’  £3.61 for 20 post free. He also sells from ebay.

[Doug Ireland]

I'll see if I can get a centre drill today.

[Steve Hargreaves - Moderator]

Never done this job Doug so working a bit blind here butwhat diameter is the magnet? Might an endmill do the job? These are pretty cheap in the smaller sizes & would work well in your pillar drill. The only problem is that it doesn't self centre so you need a good drill press with little or no play in the drill shaft...A lot can depend on the quality of your drill press....I have a cheapy unit from B&Q & the float in the drill shaft is just awful........

 

Chronos do endmills here

[Doug Ireland]

I thought about using an endmill Steve, at least it shouldn't wander off. The magnet is 4mm dia. but the problem is there is not a lot of meat in the prop driver to work with, considering the very deep groove running round it.

[Andy Green]

I've got a JE conversion kit with the intention of converting a Saito 180. I'm not convinced that altering the timing will be enough so I'm looking for a head spacer to lower the compression.

 

Would anyone know if these are being made by anyone - anywhere?

 

Andy

[Doug Ireland]

There must be plenty of Saito dealers out there Andy as they are a very popular make.

 

I put an additional head gasket in the SC 53FS, it was surprising how much it increased the gap at the valve rockers.

[Brian Parker]

Believe me guys, a centre drill will do the job.
 If you must use a milling cutter a slot drill is better than an end mill.

An end mill is a profiling tool.
Also I remain to be convinced on the need to fit head shims but watch with interest.