• Welcome to RCTalk! 🚀

    Join the #1 RC community where hobbyists connect, share, and get expert advice on RC cars, trucks, boats, drones, and more!

    • ✓ Friendly & passionate RC enthusiasts
    • ✓ RC tips & troubleshooting
    • ✓ Buy, sell & trade RC gear
    • ✓ Share builds & upgrades

Too much compression????

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
S

sidogg

RCTalk Rookie
Messages
16
Reaction score
0
Points
0
RC Driving Style
I have an HPI Nitro RTR RS4 with a .15FE stock engine. I have the rear-mount exhaust and the purple aluminum heat sink and race tank, other than that, everything is stock.

Recently I noticed that when I pull the pullstarter and my glow plug is in, it's REALLY difficult to turn the engine over. In fact, it feels like it's impossible, and I cannot turn over the engine until I take the glow plug out. After I've removed the glow plug, I can pull the pullstart and the engine turns over no problems. It even makes a nise sound, and oil/gas oozes up to the top.

It seems like it has good compression, but what would cause it to not turn over when the glow plug is in?

I've been able to get the engine started and it runs well once it's warmed up, but when it's cold, it's a PITA to turn over..

What gives??

I have, in the past, disassembled my engine completely (well, except removing the piston) but I know it is put back together the right way (it still works).

Any ideas?? :doh:

Thanks in advance,
Kevin
 
but it starts and is easier to pull once it's warmed up. if it is, how can I fix it?

I'm wondering if perhaps i have too thin of gaskets on for the new head or for the glow plug. does that make sense? I don't remember having this problem with my old head. (words I never thought I'd say)
 
Last edited:
well I'm not tottally experinced because I'm new so I'm gunna take a long shot here and say. possibly your high end is to lean and your low is too rich. but i dunno dont take advice from me at this point wait for a pro
 
Originally posted by Arrow
well I'm not tottally experinced because I'm new so I'm gunna take a long shot here and say. possibly your high end is to lean and your low is too rich. but i dunno dont take advice from me at this point wait for a pro
Click to expand...

but that is just a carb setting for fuel/air mixture...

I'm talking about I can't even make the piston go from TDC to BDC when the glow plug is in, not necessarily when I'm trying to start it.

Like, just trying to prime the engine (block off exhaust and pull pullstarter because I have a primerless tank). The gas goes into the carb a little but I can't get the piston to turn over completely during priming...

It's like when it gets to the top (TDC?) it has too much air pressure or something, and it is being blocked... as soon as I loosen the glow plug just enough to let air above the piston escape, it turns over and is once again easy to turn over...

could my ports not be lined up properly from the last time I disassembled it? how can you BE SURE they line up properly when screwing the head back on??
 
Last edited:
when you use ARO or what evr you put in it when your done running your putting too much or not wokin it in enough
 
Originally posted by Domination
when you use ARO or what evr you put in it when your done running your putting too much or not wokin it in enough
Click to expand...
This could be. I began having this issue roughly around the time I began using ARO...

How do I "work it in" or better yet, how do I clean it all out and start fresh again? :)

Can I pour some kind of cleaner into the glow plug opening (cylinder) and let it break down the oil and then some how rinse it out?
 
when you use ARO put a few drops in the carb and a few drops in the glow plug holeput a paper towel just above the hole (in the head) so yo dontgt and ARO all over the place ad just turn it over a shiz load of times untl your satified and add more if your not i persoally go overkill with ARO but thats not neccessarily a bad thing but I'm pritty posotive too much left over ARO is yor proble.
 
hi i got my os moded and they install a nova racing head the head gave to much compression they ad to call nova and what they did is shim the head to obtain the right compression but not to much because it could affect the squash band hop it helps go to ebmods.com ask ed
 
so how do I clean it all out and start over? It seems like there is some oil build-up all inside and what not.......
 
Two things are mentioned in this thread, and both of them contribute to a hard start. One, you mentioned the engine not liking to start when it is cold. Define cold. If you are talking about a cold start as in the first start of the day, fine. If you are talking about a cold start being one where the engine block is below 40 degrees in temp, expect the engine to be a pain to start.

Two, you mentioned the use of ARO. ARO does not ignite so well. When you have any ARO residue in the engine, then prime the engine, and try to start the engine...you end up with some spent fuel mixed with ARO left in the cylinder while the glo-plug struggles to do it's job. As this cycles, the engine builds up pressure in the head and eventually you will get flooded or hydrolocked (as mentioned early in the thread). By removing the glo-plug or at least loosening it, you give a release for the pressure.

My first question for you would be how old is the engine? Then what are the outside temps in the Bay Area?

Shims were mentioned. That can actually help, but as the engine ages they can contribute to weak compression. Just don't forget they are in there. That way you can remove them and regain some engine life.

You asked about cleaning it out. Take the head off the engine. Let it the engine soak in some nitro fuel for a bit...remove the carb and air filter to keep the fuel from messing with those. The soaking will break down the oil and after it dries the engine should be a little cleaner and the cylinder should be relatively free of ARO.

My personal method is to burn out the ARO. Start it up (even through the difficulty) and run it for a few tanks. Then do not add ARO unless the engine will be sitting for more than three days.

Other than that, just do not put as much ARO in the engine between runnings. A drop or two goes a really long way with that stuff.
 
OK, so the temp outside now is like 58 and I used my digital temp gauge from DuraTrax and my engine metal reads about 52' F, so I think that is OK. It's not THAT COLD. :)

I pulled the head off... How do I line up the piston sleeve? There is a little notch (arrow) on the top. Should that point directly to the side towards the pull start???

Everything looks good inside. I soaked up some of the oil, but it doesn't look like there was that much to begin with really.. hmm.
 
I usually remove the header and line up the sleeve with the block.By looking through the port
 
ok, well according to 2 other websites, my sleeve is lined up right. phew.

let me try the stock head and see if that makes things any better.. maybe it's a shim issue?

<10 minutes later>

so I put the stock head back on. SURE ENOUGH, it pulls MUCH better now...

I guess it's a shim issue... hrmph..

by the way, guys, in case you didn't know. Nitro fuel does not taste good. :D

I sucked some through my fuel line to make sure I had no clogs.. about 10 seconds after it hit my mouth and I ran into to washroom, my lips and tongue tip began tingle like crazy.. 5 minutes of washing my mouth out later, I am as good as new. :)

So I guess I need a larger shim, huh?
 
Last edited:
you could also try using 2 washers under your glow plug to releave some compression.
 
yeah, I think I'm going to get another shim for the head today and see if that helps.

Once I get this thing started, I'll be on my way to troubleshooting an overheating issue.. WEEEEEE!!

This time, though, I'm prepared. I got me trusty duratrax temp gauge... awww yeah.. :w00t:
 
Rmmmmmmmmmm.... Gotta love that sound..

HAHAHA, so I've fixed it. Doubled-up the shim under the aftermarket head and VOILA!

It runs like a champ. Even seems to keep cooler now, too. Got a new plug and reoiled things and what not...

<-------- VERY HAPPY RIGHT NOW!

:thankyou:


So, like, after it gets warmed up (240 degrees or so), what do you guys do to the guy usually? Do you lean it out or richen it up a couple clicks? Like 3-5 clicks maybe? Anyone recall which way is rich and which way is lean? (clockwise/counterclockwise)
 
Last edited:

RC Builds

Back
Top