Saito 82 Starting Issue

[Neil67]

As previously mentioned I recently acquired an Acrowot with a Saito 82 engine.

 

Got round to starting it the other day.

 

Found the plug slack, tightened. Followed the usual filling and priming procedure but on turning the prop exoerienced a very strong 'compression' almost to the point that I couldnt turn it over.  Thinking I had a hydraulic lock I remove plug and turned over engine by hand and a short burst with a starter.  Re-tighened plug.  Engine turned over smoothly with no sign of compression.  Applied starter and it fired immediately.  Repeated process several times to check engine - running well with loads of power.  Put model back in garage.  

 

Today, confused by the high compression, without fueling or anything I tried to turn prop by hand.  Back to what appeared to be huge compression force or some sort of hydraulic lock.  

 

Any advice appreciated.  What am I doing wrong. 

[Denis Watkins]

Take the rocker covers off, with a view to oiling the whole lot after inspection.

Check for broken valve springs, I use a bit of wooden dowel to push each up and down

Watch carefully for springs moving.

Check tappets have a gap

Oil up afterwards

 

Edited June 10, 2023 by Denis Watkins

[RottenRow]

Is the model stored nose-down by any chance?

 

If so, any remaining fuel in the tank and lines might be draining into the engine. If that is the case, removing the plug and turning over the engine should allow that fuel to clear.

 

Brian.

[Andy Stephenson]

I've found that the priming of Saitos is a fine balance between under and over priming, particularly when mounted inverted. Too little fuel and you can turn them over and over, too much fuel and they lock-up. Also you need plenty of current to the plug to get the engine going the first run of a session. It could be that you need to burn off excess oil which would have drained down during storage.

[Jon H]

With its 2nd hand origins and loose plug i would be taking the engine apart to make sure its not been  dismantled and then incorrectly rebuilt. I would be looking at the cams to make sure the timing is correct. 

[Neil67]

Thanks for the input.  I think it was stored nose down and maybe I just have to give it a few runs.  It started immediately after taking plug out and turning over, and when running ran very well, producing a lot of power without missing a beat.  Although second hand I think it's a relatively 'new' engine.

[Engine Doctor]

On 11/06/2023 at 08:54, Jon - Laser Engines said:

With its 2nd hand origins and loose plug i would be taking the engine apart to make sure its not been  dismantled and then incorrectly rebuilt. I would be looking at the cams to make sure the timing is correct. 

If it was incorrectly timed Jon surely it wouldnt run as well as described ?

It still might have some gummed oil in the sqish area causing the problem but rather than strip it i would try and dissolve it by filling cyl with fuel and leave to doak overnight. That is of course provided that the bearing feel ok and are not rusty . If they are then a strip and clean would be advised.

[Jon H]

Just now, Engine Doctor said:

If it was incorrectly timed Jon surely it wouldnt run as well as described ?

It still might have some gummed oil in the sqish area causing the problem but rather than strip it i would try and dissolve it by filling cyl with fuel and leave to doak overnight. That is of course provided that the bearing feel ok and are not rusty . If they are then a strip and clean would be advised.

 

Very true, but i have engines that 'run fine' cross my path often and..well no they dont run fine at all. I am not trying to insult anyone, its just that an engine can appear to run ok but is in fact well down on performance. Without RPM data on a given prop its hard to evaluate its performance. 

[Engine Doctor]

Hi Jon i understand what your saying but  engines with two seperate cams can have one cam one tooth out and stil run but be slighty down on power and poor idle , difficult to tune etc. However engines with a single camshaft means the both inlet and exhaust timing will be out. This in my experience  makes an engine run either with a superb idle and no top end and no idle atall but will start at a high speed before throwing its prop. So in this case an engine with single camshaft that runs and idles well  suggests that timing is fine. 

Just my opinion but if its not broke dont fix it .

Edited June 12, 2023 by Engine Doctor

[Jon H]

It might very well be fine, but i just take them apart now. I dont bother trying to 2nd guess what is going on and as its only 8 screws i just take them to bits. Its a good practice anyway as i check the bearings, ring, springs, bored etc while im in there. As i mentioned before, a report of running fine is not something i tend to take at face value as its not really very well quantified. A clubmate was very surprised the other week when he was commenting on how well his os gt33 was running only for me to point out it was running like a bag of spanners due to massively rich low end tuning. We had a fiddle, much better performance. Performance he didnt even know was there so assumed it was running well.  

[Neil67]

Hi Guys, update on Saito.

 

As a starting point I opted for the suggestion to fill the cylinder with fuel and leave to soak.  This seemed to work as next day the prop turned over smoothly with an obvious, 'normal' compression cycle - the high compression, previously experienced, had dissipated. I then set up the engine on my test rig.  Started almost instantly, and although I hadn't touched the mixture needle the engine ran without spewing out fuel.  Run time came out at 14 minutes for the standard kit 270ml tank (the kit tank is opaque which is a pain so I think I will try for a clear tank).

 

Sorry I don't have any RPM data - waiting on a new tachometer.  Jon, no offence taken on your performance comments, I am no expert and I'll gratefully take all the help and advice available. I'll check the RPM next time but for the moment it sounds really sweet, and there is certainly plenty of thrust when moved through the throttle range.