Engine Question?
 

Ok i got around to takin apart my grp tunned version and cleaned it all up. Once i put it all back to gether i didnt put the plug in and it turned over pretty easy and with plug in it turns over taking a lil strentgth, also this was done with pipe/header off. So my question is how can you tell when you want a new engine because when i ran o.s. mine had almost no compression and still ran strong. Also whats ur input on a pinch and who do you prefer? I heard good from speed shop and alot of locals use rayaracing and love it, but how long will the pinch last i hear a gallon then i hear people say 4 to 5 gallons?

Thanks for the help: Gage

All engines are not the same.As long it makes power and not chasing tune go as long as long as u want. And as of pinch 2to 3 gal varies for 1 gal to 5 gal if light pinch to heavy pinch.

Ok its holding tune since i had Marcel tune it lol and runs great thats why i was wondering why people junk engines when they loose compression.

At a certain point they will lose power and no longer pinch them to run well and some people do not run pinched motors for there own reasons.Or the crank pin wear too much or the rod egg shape end.In the end its cheaper too buy a engine.engine will wear out.

i know some people in my area that get Alan Burton to pinch their engines and they are getting 7-8 more gallons out of it. one guy in our area gets all of his engines pinched after 8 gallons then gets another 8 or so gallons out of them, the puts a new rod in and re-pinch and get another 4. he said he has done it to 3 other engines. all done by Alan Burton. i have only gotten one engine re-pinched and it was like new.

Well today i took it all apart and the crank is in great shape, i dont know why but the piston was black at the top but it wipped off 90% of what was there. It wasnt completly black on the top but it had quiet abit. Also Lelend just got some back from pinch and they looked brand new polished and all for 20 bucks i dont think it will hurt to try other than trashing the engine. The grp look like it hasnt seen off road lol i got it used a while back for back up and ran it a bit and the guy said he ran 20% byrons in it so maby the black was from the oil not fully clearing out???

Yeah it's carbon build up. Byron's is bad about doing it, and it's normally because the tune is off.

Figures lol i got the engine from a guy who didnt know much and once i got it i put everything to stock settings because i could tell his tune was wrong, it ran fat for about 3 tanks then i tunned it and runs perfect just was wondering why it turned black like it was lean?

im pretty sure if its lean it turns white-ish, rich usually equals rich.

Yeah it would be rich if anything. Could be other things too though, incorrect plug or shims. But probably because of the byrons and running a little rich.

in the GRP i recommend Ninja P4 plugs and byrons 30-9 fuel. also both of my needle were almost flush, it ran at 180-190 and would fly, if i leaned it some it would do the high idle crap. mine ran flawless after i started running P4s. i ran GRP #6 for a while but tune was weird.

Hello guys, I can shed some light on your pinch vs compression ?'s

Pinch is bad.... well bad for performance anyway. Pinch is there only when the engine is "seating" the piston and liner. Once those parts are ready for racing, after breakin, there should be minimal resistance with the plug out. Now compression is a whole different animal, not to be confused with pinch, but almost always is. Compression is how effective the down stroke and compression stroke are sealing within the liner. You can take a look through the exhaust port while rotating the crankshaft very slowly towards TDC and watch for leakdown (bubbles) exiting between the piston and sleeve. If the engine holds pressure inside the combustion chamber for 5-10+ seconds your piston is sealing very well. if it only takes a few seconds for the pressure to bubble out, the piston is not selaing and the engine is not running with optimal compression. Of course other parts also play a role in what kind of shape the engine is in. The rod and crankshaft are assumed to be in good condition.

The biggest thing you will notice when the piston is worn and developing alot of leakdown is the idle will continually drop throughout a run, and the tune will require a leaner mixture (making the piston expand further to seal on the liner)

In the GRP engines I would recommend the H6-H7 plugs (never use the "C" plugs in offroad), GRP plugs are made to be much hotter than any OS, RB etc plug. We have ran OS P3s before but always sacrificed considerable amount of power and idle quality over the GRP plugs.

BTW carbon on the piston top indicates the mixture is too rich on bottom and too lean on top. If you lean it on the HSN and the idle goes up, your too rich on the LSN ;)

Ok im kinda confused on the compression test seeing bubbles??? Also it seems like ur saying pinch almost means nothing, its sounding like after break in you should have no pinch? Also im running o.s. p3 plugs in it because there all i can get at my LHS.

Its actually very simple......Mechanical pinch (what your feeling) is not an indication of how much compression you have at all. A perfectly healthy engine could feel like there is no "compression" (pinch) at all without a plug. The down stroke (filling the cylinder with air/fuel mix) and the up stroke (compression stroke) determine how well the engine runs and respondes. OS engine are notorious for having no "compression" after a gallon or so, but run and idle fine. This is a classic case of the engine has plenty of compression, otherwise it simply wouldnt run.

Leakdown: Take the engine out of your car and remove the pipe... turn the engine over slowly and watch through the exhaust port, If the piston is worn excessively you'll see an abundance of bubbling around the port from compression leaking past the piston seal. Some leakdown is always present.

Keep in mind when the engine is ran hot/lean the exhaust side of the piston is the hot side and it will wear much faster. This is what causes the bubbling/leaking.

Have your local shop email me, I can get them setup with the correct plugs [email protected]