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Engine rebuilds/repairs

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stuey17/09/2008 20:02:00
607 forum posts
12 photos

Hi, i have a SC52 Four stroke which has seen better days. It has spent 2 winters in my old workshop/shed, it did have background heating and a moisture trap which may have helped. Anyway, it has not run that much, and now feels a bit notchy. I did put after run oil in when it was last run, but over 2 years is a long time to sit around! I am guessing the bearings may have corroded, along with some of the other internals possibly. Is there anyone around that does engine repairs etc, although it may not be worth doing... would serve me right i suppose.

Tim Mackey17/09/2008 22:31:00
20920 forum posts
304 photos
15 articles
Just Engines...or, if he is still going...John D Haytree.
Simon Chaddock18/09/2008 01:46:00
5672 forum posts
3011 photos

I doubt if repairs are going to be worth it as you can buy a new one for £72.50.

What do you mean by "a bit notchy?" Are you sure it has actually suffered? If the internals were suitably coated with oil, 2 years is not that long. I would simply add a bit more after oil and carefully turn over by hand a few times.

My Dads 5cc 4 stroke (now running without a rebuild) sat unused for the best part of 25 years!

Bruce Richards18/09/2008 07:36:00
1849 forum posts
I agree with Simon. Put some more oil in and turn over by hand then mount it and fuel it and run the starter on it for a while with no glow. Finally start it up and see how it goes. If it needs rebuilding now it will still need rebuilding after doing this but if its OK you have a free engine.
stuey18/09/2008 08:17:00
607 forum posts
12 photos
Thanks for the replys guys, suppose theres not much to lose trying it. I will give it a bit of after run without the plug then try starting it. If a load of rusty looking oil comes out that may be a sign!!!
Tim Mackey18/09/2008 12:04:00
20920 forum posts
304 photos
15 articles

I had around a dozen assorted engines from small 2ts right up to 120 FS that sat in a box in the loft for around 6 years - some of which were not "treated" at all - due to a rush job in gettting out of the house ( dont ask ...but the Police were NOT involved )

They sat in said box in new abode unitl I came to sell up everything around 5 years ago, and after a quick clean up, and boiling in washing tablets and hot water in a pan, they were given a good soaking in 3 in 1 oil, and then tested. Every one fired up and ran as sweet as nut.

They all went on fleabay for pennies and the Laser 90 ended up in a scale winning model in australia somewhere a year or two later.

I do of course regret selling them all as I did ( obviously ) return to the hobby shortly after - albeit now mainly leccy.

Mark Lubbock18/09/2008 14:55:00
313 forum posts
13 photos

It may be worth just taking the backplate off & having a look to see if there is any evidence of rusting on the crankshaft & the rear of the front bearing-if all looks well, the notchy feel you describe is probably due to congealed oil on the bearings-if you warm the bearing area with a heatgun/paint stripper, they may free up & a good soaking with fresh fuel should sort it.

If there is evidence of rusting (sadly quite common in four strokes) you should replace the bearings-they are available quite cheaply from bearing factors-you will totally wreck the engine if a rusted bearing breaks up!!

stuey18/09/2008 21:56:00
607 forum posts
12 photos
I don't mind getting the bearings, its the dismantling and rebuilding i wouldn't fancy too much. My Irvine 53 seems to have suffered too, it sounds like the front bearing has got noisy in that as well. I have read a post somewhere about the techniques of changing them, i'd rather leave it to someone who knows what they are doing to be honest.
Alistair Taylor19/09/2008 17:33:00
597 forum posts
11 photos

Hi Stuey

Don't be too afraid of the whole bearing removal/replacement process. It's not complicated, it just requires patience, skill in the application of brute force and a decent heat source.

First principle - mark any pieces where orientation is important, and it is possible to get it wrong.

e.g. the cylinder liner on engines that do not have a locating pin on the engine casing, and corresponding cutout on the liner, and probably the valve gear on a fourstroke. Use a permanent marker.

Second principle - don't rush

Third principle - go back to the second principle and read it S L O W L Y

Fourth principle - it is not necessary to heat ot red heat, usually a little heat (just too hot to hold) will free up seized components, smoking heat (the oil in the bearings starts to smoke) is hot enough to get bearings out.

First job - get all the bits off the engine that can be removed with a scredriver/allen key - i.e. back plate, cylinder head, valve gear covers, valve train.

Second job - remove cylinder liner. Easy peasy - stick a barbecue skewer in the exhaust port with piston at bottom dead centre, then, using a prop, turn the crank until the piston starts to push the liner out of the engine. If it doesn't work, the skewer will snap before you do any damage. Repeat the process after applying some heat to the crankcase to free if serized. Remove piston NOTING ORIENTATION and DON'T LOSE ANY TELON PADS ON THE GUDGEON PIN!!! If the piston is ringed, try to keep it inside the liner.

Third job - remove crankshaft. Best method is to press the crank out the back of the crankcase using a vice. be sure to use a soft backing (wood) at both sides. Alternative (quick) method is a weighty tap with a hammer on the front of the crankshaft, while resting the crankcase on a piece of  wood - NB this can round off the threads on the crankshaft. Practise on the cheap motors first, and use a plastic hammer if you have one.

Fourth job - bearings - heat to smoking hot, tap crank rear face onto block of wood to free rear bearings - knock front bearings out with judicious use of screwdriver and hammer.

There you go - done

Get new bearings from cos they are MUCH cheaper than anywhere else and very helpful.

Tap new bearings in using old bearings as drivers, or alternately tapping each side of the bearing to "rock" them into place.

Reassemble engine - carefully - and Robert's your dad's brother.


PS - anyone after a second hand irvine 46 with new bearings

flytilbroke19/09/2008 18:25:00
2083 forum posts
5 photos
Nice pointer, to the Bearingboys site Alister. I will have a GOOD loook later.
Eric Bray19/09/2008 20:54:00
6600 forum posts
2 photos
If you put the nut onto the shaft before you knock it out, should you burr the thread, the nut can be unscrewed and will effectively re-cut it!
John Silvester19/09/2008 23:17:00
18 forum posts

It's mighty easy when you've done it before ! If you feel happy to loose or scrap the engine  altogether-- then get on and learn by whacking about and seeing what's inside. Better still -- particularly if you are dismantling a fourstroke, buy the nice yellow book by Harry Higley " All about engines" . Start by repairing an old two stroke and get that running well , then maybe look at a "scrap" fourstroke to put in order. Alistair has lots of good pointers,but I bet he's been mending and bending  'em for years! Something very easy to begin, is to clean the outside of an engine first -- I use cellulose thinners, it melts all the gunge, especially the Castor oil lacquer found on a lot of two strokes. Also you can often free up a seized motor if caused by solidified castor.Wash the engine through with 2 t oil afterwards and then, if you need to take it apart. you won't get grit  on the innards! You'll find that changing main ballraces is no big deal ,especially if someone shows you how -- depending on the make of engine-- some crankshafts come away complete with both bearings, by removing  the 4 bolts holding the front housing to the crankcase - a real doddle. If, after reading up a bit, you  still don't feel confident there is usually someone in your club who would help,as fourstrokes are a bit more delicate to deal with. BTW --Some may disagree,but I would not use a high castor content oil in a fourstroke. Good luck -- and I bet there's not much wrong with your old SC !

 John S..

stuey20/09/2008 09:16:00
607 forum posts
12 photos
Thanks for all of the advice. I just remembered that i know an engine man who tunes and rebuilds for the 1/8 Rallycross racing guys, has years of experience. I will see if he can help me before i get the hammer out!!
Alistair Taylor21/09/2008 09:50:00
597 forum posts
11 photos

No worries Stuey

I've only been mending model engines relatively recently, having previously paid the above-mentioned John D Haytree to repair all of mine. I would recommend John most absolutely, particularly for complicated/odd stuff (he did a great job on an OS wankel that had shed its apex seals). But don't be afraid to have a go yourself on the simpler engines. Plain bearing engines (e.g. OS FPs) are dead easy to dismantle/reassemble, and being solidly built are quite hard to damage.

I started my dismantling practice on motorcycles and cars - replacing wheel bearings. You really have to whack the living daylights out of a car's front hub with a hefty lump hammer (and appropriate bearing driver) to get the bearings out


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