servicing a four stroke engine

[Martin Levy]

I plan to strip down and service a couple of old 4 stroke glow engines. What actions should I take to service and clean and what should I be looking out for when carrying this out?

thanks

Martin

[Jon H]

one thing that can be a good idea is to draw a very basic sketch of the engine on some paper and then put all of the screws on your drawing so you know where they all came from. Its also worth finding a large transparent plastic bag and removing/replacing the valves inside the bag as you can guarantee that a valve collet launched across the room will be virtually impossible to find. Also remember to make a note of the cam position. OS engines have a T mark on the prop driver to show TDC. This aligns with the casting mark on the crankcase and once in that position take a photo of the cams on your phone. There is a timing mark on the cam, but a photo can help ensure its where you started as getting it a tooth out is quite easy.

Other than that its pretty simple really, just dont rush it if you arent sure. Once its all back together turn it over slowly by hard for 2 full revolutions to make sure nothing is wrong inside. If you feel a clunk, something isnt right.

Also go easy on the rocker adjusting nuts. You dont need a 3 foot torque wrench. A little nip with a 2 inch spanner of the right size is more than enough

[Martin Levy]

Thanks Jon

are there general cleaning tasks or anything else I should be doing whilst its apart?

[Jon H]

common sense things really. just clean the engine as best you can to make sure the new bearings fit completely into their housings. if there is a small amount of congealed oil or dirt etc it can hold the bearing off by a few thou and that can be enough to mess everything up. an old toothbrush is good for cleaning the fins on the head to make sure cooling is not impeded by debris.

Once satisfied everything is clean wash the parts in methylated spirit before putting it all back together. During the rebuild, be sure to give each part a good oiling with 2 stroke oil. Dont use 3in1 oil or wd40 type oils. 2 stroke oil is best and readily available.

if you have any questions along the way pop them up here and we can get them answered

[Engine Doctor]

Hi John . Re the 3 in 1 oil . I'm glad you put that in . I keep telling people about that stuff and the damage it can do. If left for long periods it sets like varnish , and stain any casings.

Some years ago I started using air tool oil for assembly and storage of engines. It's brilliant doesn't dry out and protects well against moisture in the air. Two stroke oil is my second choice and used if engine is going straight back into service.

Two parts that are often overlooked when servicing four-stroke are the two valve springs. One or two instances over the years where they have gone soft or rusted so engine won't rev properly due to valve not seating.

[cymaz]

When removing the valve spring collets....do this in a plastic bag

[Jon H]

ED, Air tool oil is good and so is automatic transmission fluid. I was trying to keep things simple for our op so as not to bewilder him with too many options.

And you are right about valve springs. Its why we change them during the standard laser service