Magnum 4 stroke question

Good question. Proper valve train lash is certainly important - lack of lash will invariably impact performance and valve/valve seat longevity.

Seems to me all of my OS 91FS's came with valve train adjuster wrenches and the target lash value was stated in the instruction sheets.

/daytripper

I did a bit of surfing and found the info from Magnum at

Don't they supply a feeler gage thicker than the specified clearance, or was that Saito?

They may have, but I can only remember the two wrenches, and a vague recollection of an Allen key as well. I also seem to remember they stopped including those tools in later kits...

/daytripper

OS now makes you buy the valve adjusting tool separately. The kit comes with a wrench, an allen key and two feeler gages. the feeler gages are .1 mm and .04 mm.

Ah - you're right, it was two feelers, not two wrenches. I remember all the bits now - and that each small bit was individually wrapped in plastic film as well...

Cheers

/daytripper

Thanks for the link, Marlowe. I have a Magnum .52 4-stroke and a .70

Marlowe --

I have an article titled "The Care & Feeding of Four-Strokes" at my Web Site; you might find some of the information useful.

Good info, thanks.

The reason I was asking about valve adjusting is that I was under the impression that 4 stroke engines were high maintenance, mostly due to the valve adjusting. However before my Magnum arrived, in our club we have an old hand at 4 strokes and he assured me that he only adjusts the valves on his many 4 strokes about once a year. He does give them a thorough lube job with after run oil after every flying session. I cannot wait to fire it up!

It is there in the instructions or, search for the US Magnum dealer who has downloadable instructions which include the valve lash settings. 0.02 -

Thanks for the suggestion, I found this resource too:

Break it in according to the Magnum instructions (OEM or dealer). I broke mine in according to the US Dealer instructions with minimal alterations (eg. I shut it down whenever I thought it was getting hotter than I liked).

Big trick is to keep measuring the head temp (finger on head) and when it gets hot back off or shut down.

My theory is if it ain't broke don't fix it when it comes to four stroke maintenance. After run oil is about all the maintenance they get. I have one 91 four stroke that is over three years old and it has never had any adjustments except needle valves and the low end has only been set once. My other four strokes vary between 3 years old and brand new and none of them have had the valves adjusted either. I did buy the OS valve adjusting tools from Tower to get my order up to 150 so I could use the 25 off code, just in case one of the engines do eventually need the valves adjusted. Based on my Magnum 91 engines once it is broken in I think you can realistically expect 10300 - 10500 sustained RPM using 15% nitro and an APC

Regards, Charlie

That would be .002 -.004 Inches, or .04 - .1 mm

Ken

Thanks for the clarification.

Charlie,

You have made some great points. I am breaking in my Magnum 91, following Magnum's break-in instructions. That is 5 minute runs, full throttle at ever increasing RPM. Using 15% nitro, 20% lube and a 14x6 prop. Everything is going great until I push it above 8,800 RPM and I get an increase in vibration where I cannot proceed. I started with a balanced prop, but I don't have the capability to balance the spinner. I'm going to recheck the prop and try to give the spinner a try.

Marlowe