Seems to have more compression...

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PrjctStrtFrce

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After reassembling my stock motor with the same parts, it seems to have more compression now...I made sure to check the squish, but can that have anything to do with it? I spaced the magnito and the flywheel using a business card, and there is no binding there. I've had that issue once and it was noticeably louder when pulled but that is not there now. It does not sound as if the piston is hitting the top of the head. Can I damage the motor if I start it up...or should I try it?


Any thoughts?
 
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Was the head gasket good before u disassembled the motor.because those gasket are prone to blowing out causing weak compression and if yours was blown out and if u put a new gasket in and torqued it to spec.that might be why ur compression feels stronger....
 
There was no oil residue around the head anywhere, so I would assume that the gasket was intact when assembled. When I disassembled everything, the gasket obviously just shredded.

Instead of a paper gasket, I used a liquid gasket that many others have used with gasoline motors. I applied a nice even thin coat. Could it have been too thin, or did I just not have the correct amount of compression to begin with when I got the vehicle?
 
How did you check the squish and what did you end up with? If you got rid of the gasket and you're just running straight sealant, you've raised the compression a bit.
 
Raising the compression on a stock motor=good or bad? I would assume that raising it some while adding fuel (richening the mixture) would still be okay? Besides the squish test, is there any other way to know if the compression is "safe?" The thin coat that I applied was pretty close to the thickness of the stock gasket and that thing is almost paper thin to begin with, so I would assume that that alone would still be okay?

I used the solder method with a digital micro and got just above .5mm. From the videos that I have seen, they say that .5-.8mm is a safe zone. Now let's say we have two identical motors, but one has .5mm and one has .8mm squish, would the compression be noticeably different when cranking it with the pull-start?

Is this not a big deal and should I run it, or should I take the head off and make a thicker seal? If I do run it, what do I risk happening...blowing a nice hole in the piston?
 
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You can raise the compression on a stock engine without any issues. The stock gasket thickness is .020". You can throw a .012" copper gasket on it and it'll run a lot better. If you bump up compression, you'll want to run a higher octane or a colder plug. However, I've ran standard octane on full mod engines without any problems. As long as the piston isn't hitting the top of the cylinder and your squish is within spec, you're good.

You would feel a difference between .5mm and .8mm. The .5mm engine would feel tighter since you reduced the clearance between the piston and the cylinder, which means the air/fuel mixture will get compressed more. A little goes a long way with these engines.

Personally I wouldn't run it, because I don't know if that seal is going to hold. Better to put a proper gasket on it and be done with it, than trying to get sealant to suffice. If you want more compression, throw a .012" copper gasket on it.

.012" (.300mm) Copper Cylinder Gasket for RC Engines
 
The worst that can happen with the sealant as my gasket is that it can just blow the sealant, causing a bad running motor? No physical damage though?
 
If the sealant fails, some will get sucked into the engine and you'll have to clean that out. If it happens while you're bashing, dirt could get sucked in, and that's a more thorough cleaning with the possibility of having to replace the cylinder.
 
Damn it... :mad: lol

What about the crankcase gasket...I used sealant there as well...

How likely are the gaskets to blow? If the paper head gasket were to blow, then wouldn't that get sucked in a little and have contaminants from outside get sucked in?

Any chance that lawn mower shops would have those head gaskets?

How "reusable" are the copper gaskets? Are they pretty durable that they will last for many rebuilds?

What's the proper crankcase gasket that I should get from DDM? Is there a copper gasket available for that application?
 
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I ended up ordering both the stock copper and the thin copper gasket along with dd252 for the crankcase gasket.
 
the case gasket can be reused, if looks solid and no thru and thru tears. try to replace and forget about it.

usually when i reassemble i add a few drops of mix oil to the cylinder and ring. and the compression is super hi and when first fired WOW ! the sounds is freaking loud, really poppin', so you may have the oil film jumping the initial compression if any oil has been added in the reassemble effort. tighter copper gasket are my choice and fairly durable for reuse. use them with confidence.
 
...so after remeasuring the squish, I averaged about .47mm. Before I wasn't fully touching the cylinder wall, which was giving me the inaccurate reading of about .55mm. And just to make sure...I should measure the lowest squished point on the solder, correct? Because the end does not get fully squished.

Never would have thought that a fraction of a mm could make or break a motor.

Should I wait for the gaskets to come, or could I run it for a tank? :o
 
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Greggfromohio said:
I'm curious to know why the motor was disassembled? Was there something wrong with it?
Click to expand...
Here you go. :mad:

Should I run the copper gasket dry or should I put a really thin coat of sealant on it...both sides? I hope that dd252 is the correct crankcase gasket from DDM, correct?
 
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A super thin layer on both sides will do. Also, you'll need to anneal it to soften it up so it conforms properly when you tighten down the cylinder.

Here's a vid on how to do it.

[ame]

[/ame]And yes that's the correct crankcase gasket.
 
...are the copper gaskets supposed to fit perfectly or do they need some forcing onto the head? Because neither of the two gaskets that I got fit perfectly and required me to pry them around the head...
 
Is it normal to have different squish in different areas of the motor? These are the measurements that I got using .30mm copper gasket: passenger front/rear .67, driver front/rear .63, exhaust .67, carb .60
 
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