rmorhan

My Feedback: (17)

new magnum fs52ar with 4 tanks through it. the motor has very little compression & i suspect the exhaust valve isn,t seating properly( bubbles coming out of submerged muffler on compression stroke) bought a long time ago & never used so warranty isn,t gonna help. whats the best method to lap the valves & reseal them ?? any advice appreciated....thanks rob m

Jimmbbo

I would suggest checking the valve clearances per the owner's manual first, and if they are OK,
then check out this thread..

http://www.rcuniverse.com/forum/m_70.../tm.htm#705940

Cheers!

Jim

LouW

Low static compression is characteristic of the Magnum four stroke engines, apparently due to their ring design. If it starts and runs OK, just run it and don't worry about lack of static compression.

TLH101

My Feedback: (90)

If it only has 4 tanks thru it, it is still not nearly broken in yet. Needs about have gall at rich settings to break-in correctly on a "ring" motor.

w8ye

My Feedback: (16)

If you dissassemble the head to where you can look at the face of the valves, you will find that the grinder chattered on this surface(s). Not all valves on Magnums are this way but a few are. I didn't go to the link but I assume it refers to lapping the valves?

Enjoy,

Jim

Gizmo-RCU

My Feedback: (27)

I think Lou has it about right, mine doesn't show much compression and never did from new. It runs very well and is strong. Run yours for about a Gallon and then check it out again, providing it makes good enough power. It will improve greatly after more fuel is put thru it. Good Luck,
Bruce

Jimmbbo

Yep - it's a good thread on lapping valves


Can't think of any way this can happen other than air leaking by the exhaust valve seat...[sm=confused.gif]

Cheers!

Jim

Motorboy

It is normal there are leak through ring gap when engine are in static compression or the engine are running. To big gap make difficult to start engine or will not run. You can see smoke of breathing nipple at photo. My engine are diesel converted 4 stroke therefore smoky exhaust.

I has same engine as you has, Magnum 52 4stroke engine, there was leak from exhaustvalve when the engine was new. I lapped these valves with fine lapping paste until the surface was dullgrey at valves. Valves adapting at seats and will be tight when running the engine after lapped the valves. After engine ran, the compression was better than before.

Jens Eirik

Bodge

Jens,

Have you got your cam timing wrong or is your prop on back to front because, from ther picture, it looks like the engine is going backwards...?

rmorhan

My Feedback: (17)

sorry , had a blonde moment & forgot to mention the valve clearance was the first thing checked.. guess pulling the head & valves for inspection is next up. my searches on valves , valve lapping, valve reseating ect produced no results! thanks for the link & the advice.....rob m

gtisme

Motorboy,

Tell us more about this 4 stroke converted to diesel. Did you do the conversion yourself? Is there a conversion kit? I am very interested in this.

Gary

Motorboy

"The engine is going backwards" cause digital camera, never done with cam timing..


I did self when i converted to diesel.[8D]
You can read about 4 stroke converted to diesel here:

http://www.rcuniverse.com/forum/Dies..._900816/tm.htm

Jens Eirik

Jimmbbo

I would expect to see discharge from the exhaust when the engine is running, but as I understood the original post, bubbles came from the exhaust when immersed in water when engine was at static TDC, (not running). I've been working on FS OHV engines since I was in high school eons ago, and the only way I know that can happen is air bypassing the exhaust valve.... [sm=confused.gif][sm=confused.gif]

Cheers!

Jim

Motorboy

[/quote]
I would expect to see discharge from the exhaust when the engine is running, but as I understood the original post, bubbles came from the exhaust when immersed in water when engine was at static TDC, (not running). [sm=confused.gif][sm=confused.gif]

Cheers!

Jim
[/quote]

If it is much airbubbles there from exhaust, you must lap the valve. But very little airbubbles are not big problem since the pressure from combustion will press the valve at the seat and make more tight. Long running-in will make better and adapt between valve and seat.

I am working as car mechanic since 1993.

Jens Eirik

Jimmbbo

I would expect to see discharge from the exhaust when the engine is running, but as I understood the original post, bubbles came from the exhaust when immersed in water when engine was at static TDC, (not running). [sm=confused.gif][sm=confused.gif]

Cheers!

Jim
[/quote]

If it is much airbubbles there from exhaust, you must lap the valve. But very little airbubbles are not big problem since the pressure from combustion will press the valve at the seat and make more tight. Long running-in will make better and adapt between valve and seat.

I am working as car mechanic since 1993.

Jens Eirik
[/quote]

Yep!!

rmorhan

My Feedback: (17)

jens, i like your idea of further break in ( been a mechanic 20 + years & the last thing i want to do is start pissing around with a motor when i could be flying !) unfortunately, while the motor starts (electric starter), idles & transitions well it,s sadly lacking in power. it,s on a 5.7 lb giant lazy bee & struggles to gain vertical with wheels. i,m only using the wheels for breakin & it,s gonna have floats on after that so it,s gonna need more power or a bigger motor..any chance of burning a valve on these motors as on a gasser or is the combustion temp low enough to prevent that? i would have put my os 91 in it but the firewall is too narrow for the 91 to mount to. how are you guys finding these magnums powerwise? what prop are you running ? i,ve got os , ys & saito 4 strokes so maybe i,m expecting too much from this motor even with proper compression. does anyone make a more powerful motor with the same casewidth as the magnum? i,m gonna be flying off my back deck so to keep the neighbours happy 2 strokes are out... thanks for your input...take care...rob m

TLH101

My Feedback: (90)

My Magnum .52's are good runners, but not extremely powerful. Seem to be about on par with a .40 2 stroke, are slightly less.
I understand the Magnum .61 4-stroke is the same size as the .52, and is considerably more powerful.

gtisme

Motorboy,

Thanks for the link to diesel conversion of 4 strokes!

Gary

Gizmo-RCU

My Feedback: (27)

These engines require about 3/4 of a gallon or more to start to produce power. Bought one from a fellow who complained about the lack of power. Paid him a whole $65.00 and them broke it in. That was several years ago and this engine still is running great.

jaimicook

A point was made about cam timing. All the Magnum 4 strokes except the 120 are timed the same way. Run the crankshaft to tdc. With the cam cover off, the dot on the cam gear should be 1 tooth to the right (front of motor) from stright down. the 120 times exactly straight down.
JJ