fyrstormer

iTrader: (1)

If the engine is too sensitive and can't seem to hold a tune, try decreasing the compression ratio with an extra copper gasket under the cylinder head.

MonsterJuice

do you have his engine in your hand to say that? - i cant believe your still allowed to comment dribble on this site.

nitro coffee

Thanks man, so last night I went out and tested a different engine, not the GRP. I have to finish installing that in another truck.
But last night I tested my Novarossi .28 in the meantime because I was having a separate issue with that. The GRP .28 was sticking at higher revs once it got to like 20k rpm.
The Novarossi .28 was pinging hard coming down to idle off high speed passes on a rich tune. This tells me (I think) if its pinging hard on a rich tune, then it's gotta be either too much compression,
too hot of plug, or both at the same time? My question still remains- How do you know if you have only a too much compression symptom, or only a too hot of a plug symptom, or both at the same time? This is the tricky part.
What's the best way to distinguish between either too much compression or only the plug being too hot or too cold? I know head shims dictate compression and plug number is the heat range. Does higher nitro content increase compression (I think it does), and too much compression can blow plugs. But my issue I usually see is Ring aping pinging. It was happening every time very consistently. I added the shim back in it that I took out. Its back
to the factory shimming now at .9mm shim stack!! I was shocked. That's the biggest shim stack I've seen. I didn't think taking a shim out would cause that drastic of a running change
but it did. It was ring aping pinging. Adding the shim back in (used the same plug the whole time) calmed it back down almost 100% until the tank got down to almost empty and started
1 or 2 pings every so often which I didn't like. Id like to get all pings gone. With this Novarossi .28 I think Ill just leave the shim stack even after its broke in fully, and maybe go to a #6 plug
from the current #5 Im using. But it was running and idling like a champ and had a lot of power with the factory shims and a #5 plug. I guess I ended up answering part of my own question of distinguishing some of the symptoms. I only added a
head shim and the engine calmed down noticeably at idle. Id say its good to go. Next up is finishing the GRP. Getting that running well again.

Roelof

The shim stack does not have to be equal with the real head clearance but 0.9 looks like a lot.

nitro coffee

Ill post a pic of it. It seems like a lot to me too. I was shocked wen I saw it. The only thing I can think of is that the head is designed very low
in the sleeve or it has a very long stroke?

What is driving me nuts is why does it still ping here and there after a high speed pass with .9mm shims?
1 other thing I noticed is that there is a metal ringing sound sometimes at idle. I heard that is the rod?
It was running rich.

fyrstormer

iTrader: (1)

There's no hard-and-fast rule about whether the problem is best fixed with a different temperature plug or a different compression ratio. You basically just have to play with it until you get it to run well in your climate, your running conditions, and your fuel.

Pinging hard while decelerating sounds like the LSN is too lean, but if you can't enrich the LSN without the engine slowly loading-up on fuel and choking-out when accelerating again after idling for a minute or so, then the pinging during deceleration might indeed be the plug is too hot.

The general rule I use for selecting a compression ratio is to look at the range of "acceptable" tunes that I can achieve. If I have to tune the engine so rich that it loads-up on fuel just to keep it from overheating, then the compression ratio is too high and I should add a shim. If I have to tune the engine so lean that it makes bad "lean engine" noises just to make sure it warms-up properly when running, then the compression ratio is too low and I should remove a shim.

nitro coffee

So what do you think about this then? I got the GRP.28 running great again tonight. Its got the 2 needle nova carb and oring installed. 9mm venturi, reds quattro all aluminum clutch, os rp6 plug, and a .7mm shim stack on 30% nitro. I got it running great accept I cant get the lsn and idle to idle high and fast like you normally can if you lean the lsn a lot to idle high, then drop the idle like most guys suggest tuning the idle and lsn. I tried doin it this way and it would never just start idling at high revs consistently. I leaned the lsn 1 full turn and it did rise up but sounded like pinging almost, not a fast and high idle. It wasnt acting right on the low end tune. It still idled rich and still four stroked a bit when too lean on lsn. The power was there when I took off but the idle sounded rich and like it would die soon. Not a confident consistent idle at all. I managed to get it idling a little fast after it warmed up after 2 tanks of fuel but its still not idling strong, but there is a ton of compression. I cant even turn it over by hand on the flywheel in the truck after shutting it down hot. What does this sound like? Too low compression ratio? The engine came with less shims from the factory, cant remember how much less exactly. I want to post a video. Maybe tomorrow if I have time.

nitro coffee

I found the GRP manual that came with the engine. It has all the info in there. Very nice, informative manual. It is excellent. It only shows 1 shim in the exploded view. The legend for the view lists it as a .2mm. This seems super tight,
only .2mm deck height. It lists another shim but I dnt know if its optional. The view only shows 1 shim. This part needs to be more clear. The other shim listed is a .1mm but may just be optional. I think I will just put a shim stack of ~ .4 or .5mm and run a os rp6

Roelof

Then measure the real gap by using a piece of 1mm solder and squeeze it between the piston and chamber when turning the engine one turn around. The squeezed part will give the real head clearance. That should be around 0.6mm

nitro coffee

If Im going to measure the real clearance its not going to be pressing the piston against solder. I would do the caliper method measuring the depth from top of the sleeve to piston, then chamber to head and subtract them.

lunachickengril

Hello,

I am new to this forum. Reading it for some years but registered today.
May I ask how old this GRP engine is? I mean, I haven't seen an GRP engine for at least 10 years.

fyrstormer

iTrader: (1)

Do you usually make your needle adjustments in full-turn increments, like you mentioned here? Because that's WAY too much. The typical recommendation for coarse needle adjustments is 1/4 turn at a time, and fine needle adjustments is 1/12 turn (1 "hour" on a clock") at a time. If you make adjustments larger than that, you could be overshooting the ideal tune over and over.

After you lean the LSN because the engine is idling too rich, you need to lift the truck off the ground and run it full-throttle for a few seconds to blast-out all the accumulated extra fuel from the crankcase. In my experience, a very rich idle can continue to manifest for up to several minutes after the tune has been corrected, simply because the excess fuel in the crankcase hasn't been expelled yet -- especially if the engine was previously running so rich the crankcase couldn't get above ~150°F to vaporize the excess fuel. But even if the crankcase is hot enough to boil-off the fuel, there will still be a bunch of oil left behind that can cause bogging-down until it's blasted-out by running full-throttle.

nitro coffee

A lot of my tuning issues have come down to an air filter that wasnt that dirty, just a lot of onroad use. So i didnt change it in a long time. I noticed a huge difference in how much more amazing it ran when i had no filter on because i forgot to install it. It ran so good without a filter. So that led me to putting a new filter on and the engine ran great. My tuning issues and running issues have come down to the filter. The tune and running was so much more consistent with a new filter on it. It wasnt oiled either. I never knew the extent at which the filter can affect tune and running so much. I always wondered and now I know. I always changed filters for maintenance and health of the engine but it has a big affect on tune.