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Seems to have more compression...

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Seems to have more compression...

Old 05-19-2014, 01:58 PM
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PrjctStrtFrce
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Default Seems to have more compression...

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?

Last edited by PrjctStrtFrce; 05-19-2014 at 02:15 PM.
Old 05-19-2014, 03:26 PM
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Lars from Norway
 
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I will call it a go. When it is turning without touching anything it's fine. If you have changed the head gasket (i hope you have), maybe you have got one that is thinner than the one used before which is causing more compression? Have you changed the piston ring?
Old 05-19-2014, 05:40 PM
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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. 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?

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?"

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?

I can still crank it, it just takes a noticeable extra amount of effort than it did before. 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, then what do I risk happening...a nice hole in the piston?

Last edited by PrjctStrtFrce; 05-19-2014 at 05:48 PM.
Old 05-20-2014, 12:39 PM
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stock squish is around .024" (.6mm), ....017" is considered the minimum by zenoah ....stock blue paper gaskets are .020 and compress to probably .015...if you are using gasket seal without paper it'll compress down to around .005-.003" which will give you a net of around .0014". some boat guys are running .013 as an absolute minimum so i'd say you're close to that...you get into pre-ignition problems rather than striking the piston on the head...engines do not like pre-ignition. i tried running .013" before formore compression and motor was hard to start and ran hot so i aborted the idea

if you say you have .5mm (.019") then you should be looking good but make sure your solder is hitting the cylinder wall before you squash it...that's where you take the squish reading.

and i'd recommend using a base gasket rather than just goop...a properly torqued head wont leakat the base gasket...torque the bolts to 59-63inlb's and then retorque them after a heat cycle on 2 bolts, 4 bolts are usually good to go after the initial tightening

also when you rebuild a motor and use oil in the cylinder and on the ring during assembly it'll have noticeably more compression...once it fires up though and the thick oil burns off the compression will drop back to where it was before
Old 05-20-2014, 04:17 PM
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Great info! Thank you.

hmmm...maybe after torquing it, the gasket maker just got that much thinner, which is causing my "extra" compression. I will have to do a reread before I start it up and risk damaging anything. Honestly, after seeing the gasket just fall apart after taking the head off, I wanted to use the gasket maker due to the convenience and many "gaskets" that I could make from the tube. As I can see now, gassers are a little different than nitro motors, which is what I have been used to for many years.

As long as I have the proper squish, can I run with the sealant gasket, or can it be more prone to blowing? And will a blown head gasket cause interior destruction, or will it just stop running and cause an oily mess on the head and case?
Old 05-20-2014, 04:42 PM
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i'd strongly recommend using a proper gasket, they wont blow if you torque the head properly...gasket goo has it's place but it's not on our rc motors' base gaskets, a properly torqued paper gasket doesn't require any goo either...
and no a blown base gasket wont grenade your motor but it run like crap and get oily residue everywhere...gaskets cost $2...order up a few at a time so you have spares...you running a 2 bolt or 4 bolt? invest in a decent inlb torque wrench if you don't have access to one, especially for a 2 bolt ...it'll save you a bunch of hassle
Old 05-20-2014, 06:19 PM
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It's a stock 2 bolt on a Redcat Rampage MT. If the sealant were to "blow," then would bits of it get sucked into the motor along with debris from outside of the motor? If so, then would the same happen with a paper gasket?

I also used the gasket maker for the crankcase seal...is it okay there?

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?

Last edited by PrjctStrtFrce; 05-20-2014 at 06:22 PM.
Old 05-21-2014, 03:30 PM
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Most likely it will blow the gasket (seal) away from the engine rather than sucking it in as the cranckcase is pressurized during operation. It is more ok to use the gasket maker between the crankcase halfes as there is no "squish" to take in considertaion there. I think you are better of looking for a gasket kit in rc-shops made especially for this engine rather than in lawn mower-shops.

Regarding copper gaskets you can re-anneal them by using heat, in other words making them soft again as they go hard when being worked. But it is a fine line between making them softer and making them almost melt, so be careful.
Old 05-21-2014, 05:44 PM
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I figured that mower shops wouldn't have them, but thought I would give it a shot since this is pretty much a weed wacker engine.

Okay, so I remeasured the squish and averaged about .47mm. Before I was not touching the wall of the cylinder, which is why I had the 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.

I ordered one stock copper gasket and one thin copper gasket, along with a crankcase gasket. When installing the copper gasket, should I coat it with a sealant or should I just install it dry?

Should I wait for the gaskets to come, or could I run it for a tank?

Last edited by PrjctStrtFrce; 05-21-2014 at 06:04 PM.
Old 05-22-2014, 03:24 PM
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Wait for the gaskets to come, and don't use any sealant when they come, hehe!
Old 05-24-2014, 06:24 AM
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Is the annealing process needed on the first install too?
Old 05-24-2014, 03:23 PM
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No, this is not neccesary. Only when it has being "worked", in this case as in tightened down, so next time you take it off and re-use it you have to do it.
Old 05-24-2014, 06:37 PM
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...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...
Old 05-24-2014, 07:35 PM
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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
Old 05-25-2014, 03:47 PM
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I have never tried copper gaskets, but they should slide right on in my opinion, almost easier than a paper one would do. About the squish, could it be some carbon deposits fooling you?

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