spaceworm

When I am working on things that can (and do) pop or spring or jump and get lost, I do the work inside a clear plastic bag. That way the flyaways are captured.

Regards,

Richard

mike early

Does anyone use a double gasket on their back plate to keep the rod off the backplate?

Craig 01

Many glow engines rely solely on the backplate to control rearwards movement of the connecting rod,others rely on the little end of the rod and piston gudgeon boss to control location with an offset.Gouging of the backplate is cause for concern,either incorrectly fitted, worn or damaged components or excessive axial play in front bearing.
You should never need to double up on genuine gaskets.

spaceworm

Adding gaskets also increases the crankcase volume and reduces the pumping efficiency, lowering power.

Richard

Craig 01

Only in the case of two strokes and YS fourstrokes in which case the gasket sets the disc valve to crankpin clearance.
The miniscule increase in crankcase volume on a twostroke would not be noticed,however,if the conrod rode the crankpin at its most rearward point of travel accelerated bigend wear would be noticed on engines that rely on the backplate to set axial play.
General model fourstrokes crankcases are open to atmospheric,not sealed,including Saitos.

mike early

The front bearing feels very perfect. But since I am replacing the rear bearing, I shall replace the front bearing as well. But, I do not expect the exchanging of front bearings to remedy the situation.

Craig 01

It is always wise to replace both crank bearings as a set.
Check all components carefully whilst disassembled you will find the cause of your problem if in fact there is a problem.

airraptor

My Feedback: (66)

I havent read thru all these threads but did read the notes sticky. need to know how to time the cam gear on a 125. I put the dot at the bottom crank at TDC. Sound right?

w8ye

My Feedback: (16)

That is correct

Craig 01

Sounds about right.
Crank at TDC,camgear indicator dot directly down.You can stick a drill bit,wire rod through the inlet cam follower bore with lifter/follower removed that fits perfectly in the lube/timing locater hole on the base circle of the inlet cam.Centre your locater in the lifter bore and place the cam cover squarely over its mounting on the case with crank at TDC.

w8ye

My Feedback: (16)

This is the way I have been doing it for years

However, with the Saito's with the flat plate cam cover it doesn't seem to work as handy as on the round cam cover engines. If you seem to have trouble, you can try the razor blade or Exacto blade stuck in the gear teeth along he side of the cover while inserting.

Find something that works for you

airraptor

My Feedback: (66)

thanks guys.

Craig 01

Yes,i do it this way also when lifter is mushroomed slightly and cannot be removed and is not necessary to remove cam from housing.

w8ye

My Feedback: (16)

When you are assembling a Saito, you need to chaeck the timing before completley finishing the assembly.

After assembling the cam cover with the crankshaft at top dead center, - - -

If you turn the crankshaft one full turn (360 degrees) you are then at the overlap interval of the cam lobes.

If on the overlap interval, this overlap should come across TDC.

You can find the point where both valves are open the same amount. One valve is closing and the other opening no matter which way you turn the crankshaft and the valves are both open the same amount, the tops of the rocker arms will be level with each other, The exact center of this point should be about 5 degrees before top dead center when turning in the direction that the engine runs.

This overlap period where both valves are open can also be determined by blowing in the exhaust pipe and the wind comes out the open carburetter.

On a Saito, top dead center of the piston can be done by a tooth pick in the glow plug hole, feeling of the compression wanting to push the piston down, or looking at the crankpin when the rear cover is off.

What ever you feel comfortable with

Craig 01

Or a simpler method on full overhaul/rebuild is before inserting the inlet lifter and having placed the cam cover, insert and rundown a couple of screws into cam cover after centreing it over crankcase,look down the inlet lifter bore with crank still set at top dead centre and locating hole will be in the approxiamate centre of lifter bore,one tooth either way will have the cam locating hole to the outside edge of lifter bore.Reassemble engine when checked good.
Actually,one can advance or retard the cam a couple of degrees by simply moving cam cover one way or the other against cap screws.I have not checked the difference either way in operation as i always set the cover centrally.Although in full size 4 stroke engines i have dialled a cam a couple (or more) degrees to improve or (lower idle speed) or increase top end power or move the torque curve to suit gearing depending on setup of engine build and a couple of degrees either way makes a very noticeable difference.

mike early

I've always shot for straight-up when taking stabs at this. Tonight, when I install new bearings in my 180, I will try for the 5º BTDC you describe here. That's about 1 tooth of the cam gear, would you say? Do the cams have 72 teeth?
Looking in the back cover, the crank pin will be at 12:10 on the clock, and not high noon.

They all run pretty well. But I guess I've left a little top-end performance on the table by retarding all my cam-timings

Swifter

My Feedback: (1)

I just "inhereted" a Saito 325 5 cylinder radial. It's in very rough shape. I.E., been crashed a number of times. It does NOT turn over easily even w/ the plugs out! Can someone please direct me to a reputable reliable Saito repair person other than Horizon Hobbies that will not cost me an arm and a leg? I'd greatly appreciate it.

Also, I'd like to hang it on a Raidentech 120 Gee Bee w/ a 71" wing span. Too small? I have no experience w/ this engine. What prop would I use? What wing span/weight can this engine handle? Thanks guys.

Oh, also. I saw where someone wanted to know how to get the front plugs out. I can easily do it w/ a QUALITY thin wall Sears Craftsman deep socket. 5/16"

Swifter

w8ye

My Feedback: (16)

http://www.bj-model-engines.com/home.html

It's going to be expensive even if you do it yourself

RC Specialties

Paul,

I will send you a PM.

Jim

w8ye

My Feedback: (16)

Share your experience with us on this. I may not be explaining it clear enough?

mike early

I always assumed the dots were lined up with the crank pin and centerline of the cam shaft lobes. From what you are saying, the cam is meant to be advanced a bit. Perfectly understandable, I've degreed cams in my Small Block Ford many times. Even have a cam wheel and dial caliper, etc for this procedure.
You've mentioned this before. My apparently retarded (no pun!) situation yield a great idle, but gives up top end, I think you've said. I had forgotten that. But I don't think I've replaced any bearings since I read your post, and since forgotten. I am glad you reminded me. I got plenty of room on the idle to give away. It idles at 1500 with a 16x10x3blade. 2000 would be fine.
I didn't get a chance to pick up the bearings from the LHS today. I'll install them tomorrow night and take a photo of the crank-pin through the open back plate when both valves are open the exact same amount. I"ll shoot for 1 tooth BTDC.

Where did hear about the 5º advanced? I guess if you are positive the dots are lined up, and that's what it turns out to be, it's self-evident. But I can never be sure where them damn dots end up after I've slid everything together.....

ZachB10

My Feedback: (9)

How do you like that turboheader muffler? Worth the $70?

P47 Jug - Al

My Feedback: (1)

Some feedback. First, thanks W8YE and Tarasdad!

After getting the valves to move smoothly, the rpm's on the 15x8 went from 7100 to 8500. I also checked valve clearance but it was almost right on. 8500, hmmm. Don’t know if that is still a little low, and that's peak rpm. If I remove the cylinder to clean the valves a little better, can I get into trouble? Meaning parts will go flying. It's looks pretty straight forward to me. Or is 8500 acceptable? I'm using 15% Wildcat.

w8ye

My Feedback: (16)

What we are shooting for is that the valve overlap interval is to cross over TDC on the overlap stroke. But if the cam is set with the dot at 6:00 and the crank pin is straight up then from my experience, the exact point where both valves are cracked open a slight amount (the same amount level across the rocker arms) is slightly before TDC and not exactly on TDC.

This over lap is the period where booth valves are open a little bit even though one may be open more than the other. This band actually covers some 25 degrees? It will vary by your valve clearance settings. You can see the range of it by blowing in the exhaust with the carb open and observing the air coming out the carb during the overlap period.

The Saito has more teeth on the cam gear than the Y-S, OS, Magnum, ASP, SC etc so one tooth off may be hard to figure out? On the other engines, you can pull the cam cover off and see where the cam is.

I had a ASP 120 that would only turn a 15 X 6 good. It was sick with a 15 X 8. I looked at the cam and it was one tooth advanced. I set the cam back one tooth and that engine screams with a 15 X 8. Saitos are not so drastic being 1 tooth off and will still run pretty good but they run best when set correctly.

The way the logic goes, if you are advanced one tooth, the idle is great but you loose the ability to swing an inch of prop.

If you are retarded one tooth, the top end is great but it will not idle worth a toot.

w8ye

My Feedback: (16)

P-47

Getting valves out of a used cylinder is a real P.I.T.A. The top edges of the valve stems and the top edges of the retainer ring groove get a flashing on them and the valve will not go down through the guide. In some cases, it is difficult to even get the spring retainer off the valve. You have to go in there with a riffle file and try to get the flashing off the valve stem. You will spend an hour on each valve just trying to get it out of the head without scratching the valve guide.

On a broken head this is not too bad for you can drive the valve down through the guide and clean up the stems with the valves out of the heads. Goes a lot easier.

You best just try your luck with cleaning the valve stems through the ports. The intake stem is usually clean.