Un-even cylinder temps

[Martin Fraser]

Hi folks,

As per title - the left pot on my Saito FA60T seems to be running a bit hotter than the right. The rubber boot on the induction tube seems good so what else could cause this on a single carb engine? Both plugs are OS Fs and running on Opti 4 stroke 15%.

Cheers, Marty

[Denis Watkins]

How is the measurement taken Martin?

[Martin Harris - Moderator]

Is one too hot or the other not getting to normal temperature?

Valve clearances, piston ring not sealing, poor cooling airflow?

Edited By Martin Harris on 18/05/2017 21:17:06

[Martin Fraser]

Hi Denis,

Just gripping them with my little pinkies right after landing. Not scientific I know but my club mate thought the same.

The right pot seems normal i.e. you can hold it for about 5 seconds before it gets uncomfortable but the left is more like 2 seconds, sort of ouch!  I took care setting the valve gaps but will re-check.

Cheers, Marty

Edited By Martin Fraser on 18/05/2017 21:23:45

[Denis Watkins]

You would expect they were the same, but there are so many variables as MH suggests, one cylinder could be in cooler air, one thou difference in tappet setting too, but you make no comment on the running, which I bet it superb.

The career motor guys will be along shortly

[Devcon1]

Not sure if this helps but my ASP twin does something similar, I'm told it is because the inlet tubes are not identical in length.

[Jon H]

If its running fine then ignore it. With a single carb it will never be perfect so just run it and be happy

[Martin Fraser]

Posted by Martin Harris on 18/05/2017 21:14:01:

Is one too hot or the other not getting to normal temperature?

Valve clearances, piston ring not sealing, poor cooling airflow?

Edited By Martin Harris on 18/05/2017 21:17:06

Hi Martin,

Although it's quite an old engine and not run since 2000, it has been well stored and like new inside - very clean and no play in anything. The air flow over the pots is symmetrical so I'll recheck the tappets and get back to you all.

Many thanks for your input, Marty

[Former Member]

[This posting has been removed]

[Martin Fraser]

Well I checked the tappet gaps yesterday and they allowed the Saito feeler gauge to slide in without any pressure - just a wee bit of drag. So off to the club field and got another four flights in, landing several times during each flight to check on temps. No discernible difference in temperature!

I'll take your advice Jon and just fly.

Cheers, Marty

[Jon H]

its the best choice martin. I often have calls asking about one thing or another and my response is always the same. if its running well, leave it alone and just enjoy it

[Engine Doctor]

Do both cylinders have similar compression? If one is lower then that will cause the difference. I had a similar problem with a Magnum (SC/ASP) 160 twin. One cylinder ran really well but the other which had slightly lower comp would run cooler and occassionally go out. I tried all sorts to cure that but the heads were rubbish and distorted when tightened down.  .As it's a Saito it is much higher quality than Magnums . Suspect a bias in the inlet tracts. As John says if it runs well then leave alone .The cylinder that is hotter sounds about right as the run a lot hotter than two strokes. 

[Jon H]

Posted by Engine Doctor on 20/05/2017 21:53:37:

Do both cylinders have similar compression? If one is lower then that will cause the difference. I had a similar problem with a Magnum (SC/ASP) 160 twin. One cylinder ran really well but the other which had slightly lower comp would run cooler and occassionally go out. I tried all sorts to cure that but the heads were rubbish and distorted when tightened down.

I had the same issue with an asp 160 I have. I have not managed to fully cure it but I did improve the situation by modifying some old pistons from a laser 75. By pure fluke they are the same size as the ones for the asp 160 so I was able to fit my engine with new twin ring pistons and some Laser 75 piston rings. As the rings I had were old its not perfect but it has improved the engine no end. I can send you some pistons if you fancy giving it a go yourself

I have never had/seen the head distortion issue though

[Engine Doctor]

Hello John . Thanks for the offer but got rid of the engine some time ago . It was ok at full throttle but unreliable at lower throttle openings and had to have a on board switched glow for idle. The culprit on my engine was the cylinder head distorted when it was fitted to the cylinder and the distortion affected the valve seats .Even very light tightening of the head bolts caused the distortion. I took it back while it was under warranty and the supplier spent hours seating the valves. He tested the seating with thinners and the seal was perfect. As soon as it was fitted to the cylinder the seal was distorted. He eventually after a few attempts as seating the valves had to agree with me and fitted a replacement head . It was still down on compression even with the new head as that wasn't much better than the original so it had to go. . I often see this problem with the budget four strokes and the owners are fobbed off by the suppliers/shops being told that it will get better with more running in ! It doesn't. Budget engines ? you get what you pay for. If I'm asked to help sort a SC,ASP, Magnum with tuning for idle and it has low comp I don't waste my time now but tell the owner to back it to the supplier. . There are plenty of good SC etc out there but if comp is low don't bother , they are IMO only good for door stops ,fishing weights or cutaway display engines .

E.D

[Jon H]

You wont distort one of our heads i can assure you!

As for ASP/SC 4 strokes, running them in like an ABC two stroke really helps the compression and they tend to work much better. on a 52 i would use an 11x6 and after pre oiling the rockers and bottom end i fire it up, run it quite rich for 2 mintues or so at 1/2 throttle before opening to full power a very quickly tuning for about 90% of peak before throttling back. another 5 minutes of throttle wagging with short (5-10 second) bursts of full power has the ring bedded in nicely. Once stopped i let it cool, then restart, set the slow run, peak the main needle and go fly, taking care not to use full power for more than a few seconds. After 3 or 4 10 minute flights i fit whatever prop i choose and then fly it like i stole it, which is appropriate as the only ASP's i tend to deal with are i the front of my students models!