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Old 11-23-2009, 04:46 PM   #1
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Default First Time engine tear down questions.

Hey all. Doing my first engine tear down and have a few questions.
There are three copper head shims and I'm just wondering if they are all needed and if not what changes will you see either adding or removing these shims. I know that you don't want plug to hit piston but just need some info on it.

What other things should I be looking for when stripping motor.
Have found some small rust spots on the crank but thats my fault being lazy with ARO. Is it ok to give it a hit with fine wet and dry paper?

Also noticed swirl marks on top of piston. Is this from running to lean or something else. Will atach photos but looks like camera just died.
Cheers
All help will be much appreciated.
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Old 11-23-2009, 04:58 PM   #2
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Main thing to remember when tearing down any engine is cleanliness cleanliness cleanliness!!! Keep everything placed out the way it came out and make sure you use lots of assembly oil/after run oil when assembling it back together again.

If the engine came shimmed that way leave it that way if it has been running fine, if you add shims this will lower the compression generally allowing you to run a higher nitro content safely, if you remove shims it will increase compression and i wouldnt recommend it, i doubt removing the shims would allow the piston to come in contact with the head button but you dont want to run it with to high compression anyway, to much stress on everything and its not needed.

A couple of small rust spots arent to bad, chec the bearings for play and smooth rotation, make sure they are clean of any rust or corrosion markings, i would use a scotch brite pad and then some after run oil on the crank, make sure to flush it very well first and dry it with some compressed air before oiling it to prevent further corrosion. Stay clear of the intake port area and conrod pin on the crank if you decide to give it a clean up, you dont want to scratch these areas with anything as they run like a bushing on these parts of the crank.

before re-assembling it check over all your o rings/gaskets to make sure they are fresh, i replace them everytime i tear mine down just to make sure i dont develop an air leak anywhere. Also oil them well before sliding carb necks or pushing back plates in etc. so they dont tear.

Lastly dont over tighten the bolts, the crankcase is only aluminum and the thread is fine, you dont want to strip the threads out or its an expensive mistake.

lastly cleanliness cleanliness cleanliness !!
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Old 11-23-2009, 05:14 PM   #3
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thats good info i never rebuilt a engine ethier,i do have a question about a nova .21 bf it says its shimmed for 25% and i run 20% do i take one off or just leave it i already tune it once already
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Old 11-23-2009, 06:28 PM   #4
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I have taken the crankshaft and soaked it in denatured alcohol, then let it dry, the I hit it with a polishing bit with a dremel on low speed until it's shiny. Then I soak it again in clean denatured alcohol, then lube it with some after run oil.
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Old 11-23-2009, 06:45 PM   #5
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Pics of marks on top of piston is this from too lean?
Piston very discoloured on exhaust port side? Is this a tell tail sign of running too lean.
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Old 11-23-2009, 06:51 PM   #6
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The swirl marks are from when the piston was machined. You didn't say what kind of motor it is, some motors you can take shims out and be safe but most you can not. Also depends on nitro %.

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Old 11-23-2009, 07:11 PM   #7
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The motor is an old nosram 7P rs.21 and I run 25% in it.
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Old 11-24-2009, 12:05 PM   #8
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There is a small amount of wear in the con ron crank pin bush. How much is to much and how do you measure?
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Old 11-24-2009, 07:16 PM   #9
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I have another question to add to this thread, how do you get your engines so clean before tear down? i have been thinking about doing a tear down but i can never seem to get the engine clean enough to feel comfortable opening it up. i have used nitro spray on the outside of the engine to clean off some dirt but it doesnt get it all off, the dirt seems endless. is there something i can soak the engine in and then brush the dirt off?
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Old 11-24-2009, 08:19 PM   #10
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Although it's expensive for some, I find a compressor to be a very valuable tool when cleaning an engine. I use a brush to knock off the heavy dirt, then a solvent such as Simple Green, nitro spray or denatured alcohol. Lastly, I hit it with some WD-40 then blow off all the excess and any residual dirt with the compressor. It's not necessary, but I like to use the WD-40 to keep the aluminum from getting too "dry" and stained with chemical marks. In the absence of an air compressor, I buy a pack of soft shop towels from home depot and use a fresh one for each rebuild. They're pretty cheap and the dirty ones work well for everything else once they've been used on an engine. Don't soak the engine - it will just let dirt and grime get into parts of the engine that would have otherwise remained clean.
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Old 11-24-2009, 08:35 PM   #11
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Quote:
Originally Posted by H9_nutter View Post
There is a small amount of wear in the con ron crank pin bush. How much is to much and how do you measure?
The best way to measure the crank is with a Micrometer, they are not very expensive. A caliper can give you a decent measurement but not nearly as accurate. There are not too many that can measure a rod bushing, I use a bore guage that measure's within .0001 inch. Even when I resize sleeve for people I tell them what the rod wear is. With experience you can feel the rod on the crank and tell if it's too much but it is still a guess.
For the money your best bet is to send it to someone that can measure all theses things and feel the bearings and have the tools to replace bearings, etc. I only charge $35.00 to rebuild a motor and it includes sleeve resizing. (not parts)

As far as cleaning a motor, I tear everything apart, take out the front bearing, take off the carb. I use a Hotsy high pressure washer and put the motor parts in a basket. It uses Alkalai hot water, everything comes out more clean than it was new. I usually pop the seal off the front bearing and wash the bearing too, then I decide if it is worth reusing or not.

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Old 11-24-2009, 10:40 PM   #12
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I only tear into my engines when I have a problem. If it is running god, not flaming out, no strange noises and not leaking out of the front bearing then why tear it apart. As for the rod when it's put togeather turn the flywheel throgh the compression 1 full stroke and when it's in the compression range rock the flywheel back and forth and see if there's any play you can feel. If it feels like it slips replace the rod if it does not then I would say it's ok. Front bearings can go out and need to be replaced and rear bearings can go out and need to be replacedas well. But I don't see any benifit to tearing into an engine that's running good just to clean it. It's not dirty it's all sealed up and all it sees is fuel so why clean something that's not dirty?
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Old 11-25-2009, 09:16 AM   #13
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H9 are you from the crcmcc club in cairns? Think I seen you
posting in the club thread? Think I might have ran into you at the intercity this weekend just gone if you were there, I was driving the white rc8b and yellow rc8t that was steering like a shopping trolley with a broken wheel due to an unseen broken servo saver my name is Noel btw
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Old 11-25-2009, 11:34 AM   #14
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Hey Noel,
I'm from tsv and nah I didn't race on the weekend. I did come to cairns that weekend but I had a wedding on Saturday in mosman, but I did come to the track on sunday to take a look. Liked what I saw but a little shade would be good. I haven't run the cairns track yet but will in the future. I'm only starting out (6 Months) in the racing seen but have had nitros for a couple of years but used to just bash around and annoy the neighbours. I've had the current motor for a while and it never got looked after never aro and the thing would sit for months. Supprised it only had small rust spots on crank

Last edited by H9_nutter; 11-26-2009 at 11:58 AM.
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