F2T with blow by??????

gimpy · #16 (**permalink**) 02-20-2010, 06:00 PM

Quote:

Originally Posted by Kyrasis6

Since you have the pistons out now it would be a good time to use some sand paper to deburr the edges of the valve reliefs and anything else sharp on the top of the piston. Do the same for the edges of the combustion chamber, especially the edges of the squish area.

Since you have a mill do you want to tweak the pistons a little bit? I know 2 places where they can be lightened safely.

Is there a ring in the valve relief on #4 cylinder for the valve that warped/bent? It could have floated and smacked the piston or it could have just been pure heat. If the machine shop hasn't finished with the head yet you might want to call them and give them specific instructions to make the seating area on the exhaust valves a little wider. Most of the cooling of the exhaust valves is done through the valve seat so making it a little wider will help keep the exhaust valve cooler.

K6, I am considering polishing the piston crowns to help them not absorb as much heat(smooth surface is less than a rough one)No there are no marks on the top of #4 nor where there any on the valves(first thing I looked for having missed 3rd gear,I hate when I do that)
So where can I tweak @?I always like a little tweak!!!
I'll call the shop where I took the head ,the fellow there is a long time hot rodder that runs @ the local strip and loves a little tweak too.We had a long talk about this head,& he understands that it is a turbo settup,he will likely be happy to give me a bit more margin on the exh. valves.
Gimpy

fredio54 · #17 (**permalink**) 02-22-2010, 12:00 AM

what do you mean "more margin" on the ex valves? wider seats than stock? you basically have a setup that was designed BY MAZDA to do almost exactly what it is doing, I definitely wouldn't mess with the seat widths if I were you. If that's not what you mean then explain to the noob from down under :-)

As for polishing the tops, deburr and polish are both good, both will help keep heat out and deburring will also remove any potential places for preignition to attempt to happen. While you have the head off you could give that a wire wheel too :-) Wire wheeling is a great way to buff up alloy, if you are gentle.

I have a question:

Did you ever look for blowby before? Or did you just open it recently and go "shlt, that is a lot" and put it down to the recent thrash? Turbo motors push out a lot more than NA and it's pretty normal to have a lot of gas and condensation from it in there. My engine has no mods in that way, yet. But I know another guy that has widened his to 1/2" and added a second large one too - problems of blown seals and leaks all gone, less milk/cream too. Just a thought.

Fred.

Kyrasis6 · #18 (**permalink**) 02-22-2010, 12:44 AM

Quote:

Give them specific instructions to make the seating area on the exhaust valves a little wider. Most of the cooling of the exhaust valves is done through the valve seat so making it a little wider will help keep the exhaust valve cooler.

From: The Internal Combustion Engine in Theory and Practice Volume 2: Combustion Fuels, Materials, and design, by Charles Fayette Taylor.

Page 531 End of Paragraph 1: "The most important path for heat flow (75 percent according to ref. 12.21) is through the valve seat while the valve is closed."

Page 531 Paragraph 2: "...even a small reduction in valve temperature, as from 1400 to 1350 degrees F (777 to 750 deg C) results in a marked improvement in valve life and reliability."

"The designer should strive for even lower temperatures as far as possible"

Page 531 Paragraph 3: "For a valve of given size it's temperature may be minimized by:

Minimizing heat-receiving area by extending [the] valve guide boss as near to the valve head as possible.
Maximizing heat-rejecting areas, that is, valve seat and valve stem areas.
Minimizing length of path from valve guide and valve seat to coolant
Maximizing valve heat conductivity by generous valve-head thicknesses."

Keep in mind many of those things are a performance trade off for more reliability, extending the valve guide closer to the valve head has a negative affect on air flow, increasing the contact width of the valve may have a negative affect on air flow, increasing valve stem area increases valve weight as does using a valve with a thicker head margin. I do not know what the factory manual for that engine calls for but the B2200 factory manual calls for a seat contact width of .047-.063" if anyone wishes to adhere strictly Mazda's specification then the exhaust valve seat contact should be as close to .063" wide as possible or whatever the factory manual for the turbo engine specifies. If the valves and seats machined via CNC as most machine shops will these days do not lap the valves afterwards.

Quote:

You basically have a setup that was designed BY MAZDA to do almost exactly what it is doing...

I'm pretty sure Mazda didn't design the engine to run 14 psi of boost and their main goal is profitability, not satisfying Gimpy's need for speed which means there is always room for improvement.

dealwithit · #19 (**permalink**) 02-22-2010, 02:07 AM

Quote:

Originally Posted by Kyrasis6

I'm pretty sure Mazda didn't design the engine to run 14 psi of boost and their main goal is profitability, not satisfying Gimpy's need for speed which means there is always room for improvement.

yes, this stands for pretty much anyone thats modifying the engine in there truck, be it that came from a high performance car or what not.

gimpy · #20 (**permalink**) 02-22-2010, 04:53 AM

Quote:

Originally Posted by fredio54

I have a question:

Did you ever look for blowby before? Or did you just open it recently and go "shlt, that is a lot" and put it down to the recent thrash? Turbo motors push out a lot more than NA and it's pretty normal to have a lot of gas and condensation from it in there. My engine has no mods in that way, yet. But I know another guy that has widened his to 1/2" and added a second large one too - problems of blown seals and leaks all gone, less milk/cream too. Just a thought.

Fred.

Yes Fred,the first thing I looked for on first fire up,and a little check every time I've changed oil(it's a good indicator of whats going on in there),but this event was extreme,it pushed the dipstick out of tube and blew oil everywhere,also was blowing oil(not vapor out of the breather (little K&N style) in the valve cover.And yes this motor had more air movement then the 6.3 liter in the Chevy before this event.
That all being said,I pulled the rings from the pistons yesterday PM,and found this little thing on the #4 where I had found a carbon streak on first examination

Broken apparently for a long period,as shown by the carbon behind the break,held in place by an uneven edge under the 2nd ring(the piece fell out after I pulled the 2nd ring)Now I am sure I've found the cause of blow by.
A new std. piston is on order & should be here in 4 or 5 days.

K 6, where can I safely lighten these pistons?
Gimpy

dealwithit · #21 (**permalink**) 02-22-2010, 10:53 AM

congrats! nothing better than finding the problem, and it not being a huge deal to repair.

Kyrasis6 · #22 (**permalink**) 02-22-2010, 11:46 AM

Nice...

I just got my example piston out of storage yesterday, I'll take a pic and mark it up. I'm not sure if the weight will throw the engine off balance though, if it was a race engine would say it woudl need to be balanced afterwards but OEM engines aren't balanced worth crap so I don't think it will hurt.

gimpy · #23 (**permalink**) 02-22-2010, 04:08 PM

Quote:

Originally Posted by dealwithit

congrats! nothing better than finding the problem, and it not being a huge deal to repair.

Thanks,but right now feels like another piece on the pile!!!!
Gimpy
That would be great K6!!

fredio54 · #24 (**permalink**) 02-22-2010, 04:23 PM

I stand by my statement about the valve seats. My head specialist wants to narrow mine up if he ever gets hold of one of my heads - he knows his stuff and wins many races for customers. I'm not sure if I'll let him, but he has considerable experience with all sorts of modern stuff including a large percentage of jap engines such as rb26dett etc. I understand that the valve temperature is down to cooling capacity from stem/seat, but reality is that it's a non-event. If it ain't broke, don't fix it!

OEM US engines might not be balanced worth a crap, but the jap stuff is fairly good out of the box when not modified. As for piston mods, provided they are consistently modded and weight matched it will not be an issue. The balance is largely down to evenness, not rod-piston-crank relationships.

Bummer about the ring land. Did you verify your higher boost settings with some datalogs before beating on it significantly? The carbon staining on the back side would probably happen pretty quickly, so don't rule this out as being tune related.

If you want to get your tune honed and good, I'd suggest posting your msq files and datalogs to a thread somewhere and seeking feedback. If you don't have knock sensing or some modified earmuffs (what do you guys call those?) with tubes to the block then conservative timing is a winner.

Right, I have to run off.

Fred.

Kyrasis6 · #25 (**permalink**) 02-22-2010, 11:51 PM

non-event? He clearly had some sort of valve failure in addition to the piston getting hammered, of coarse we don't know if it was bent, warped, or just badly carbon pitted. The best way to tell would be to check the harness of it with a rockwell tester in comparison to a new valve, if it is a bit softer then it has been annealed and a sure overheating problem of the valve, if the hardness is pretty close to a stock valve then it is probably just a fluke from being over revved. The broke piston can be checked the same way if it has soft spots then it is likely that detonation or overheating has contributed to the failure. Just like the piston a failure could be a matter of the circumstances, the failure may not be immediate either. Way to often the difference between and engine that will take a pounding and one that gives up is the "that should be good enough mentality".

Experience is all relative as well, a good example of this is a 1/4 mile drag racing engine versus an oval track engine. The owner of the valve company I worked for professionally built his own engines and raced in NHRA for years, sometimes we would be running spring retainers and make a few with an 8 RA surface finish from a worn out insert in the CNC lathe. I would be tossing them because they were way out of spec and he would say their fine, when they were running in an 8,000 hp engine for only a 4 seconds under load they never had time to fail. Shortly after I left he expanded his business into NASCAR and attempted to pass the same surface finish on a retainer in an engine with 1/10th of the power, he got a wake up call when the retainers were sent back to him in pieces and only 5-10 laps on them. The guys been racing and building drag racing engines longer than my dad has been alive...

The reason why many race engines are rebuilt every season, or after every race is because they are sacrificing longevity for performance. Running a smaller seat contact width does offer performance options that may run flawlessly for that season, doesn't mean it will run great the next season that smaller contact area may cause the valve to slowly anneal over time and it might take 2 seasons for it to get soft enough to cause a failure. On Gimpy's street truck that sees more miles and more heating/cooling cycles that could be a year or less.

Other things to consider not related to racing experience would be the types of engines and their designs, the rb26dett uses 4 valves per cylinder (correct me if I'm wrong). One of the many reasons for using multi-valve designs is the increase of seating contact area versus surface area resulting in better cooling. Although Gimpy's engine is a multi-valve design it only uses multiple intake valves per cylinder, it doesn't really help the intake valves much for cooling purposes because they generally get all the cooling they need from the intake charge. Since his engine only uses one exhaust valve per cylinder they basically have the cooling capacity of the 8-valve head, if he plans to drive his truck every day for a few years and thrash it like he does it would be wise to at least use the maximum contact width the factory recommends. Probably doesn't make a lick of difference on the intake side in terms longevity from added cooling.

As for the tubes going into the engine bay, we duct tape a midget to the hood with a long handled screwdriver to do that. I believe the instrument your referring to though is called a stethoscope in the US.

Gimpy, I'll try to take pictures of the piston tomarrow and mark them up, I agree with fredio since the mass of the pistons is reciprocating and there are always two moving up while two are moving down that you should be ok as long as each piston weighs close to the same. Our engineers at the engine shop didn't seem to care at all if the overall weight of our connecting rods were out by as much as 5 grams as long as they weighed the same and big end weight was spot on.

dealwithit · #26 (**permalink**) 02-23-2010, 12:56 AM

i see where your coming from k6 with the single vs dual exhaust valve thing, being fred's got 2 exhaust valves thats probably why theres no issues with his.

im sure lots of people run these engines at higher levels that we are tho and not having these issues?

gimpy · #27 (**permalink**) 02-23-2010, 05:32 AM

Yep ,and Fred's motor breaths better on the turbo.I'm in with K6,any engine I've ever ripped apart that was built for long term service had wider seats,when I quizzed about it was always told for better valve cooling,longer life of the valve.This "ain't no tractor" but it's not a 1/4 miler,or F1 either.
If I can stay @ the wider side of the spec. I will.I had a set of 1600 VW heads built with a narrow seat/5 angle valve job,cooked an exh. valve in less than 20,000 miles.Better power?It was a 1600 VW,any little bit helped.But 20,000 mi. was not good.
Gimpy

dealwithit · #28 (**permalink**) 02-23-2010, 10:41 PM

so gimpy, ever put any thoughts into a bigger turbo maybe????

the guy that i traded my truck to built a full tig'd stainless mani and put on big dodge diesel turbo, i think its the same one that fred has on his?

Kyrasis6 · #29 (**permalink**) 02-23-2010, 11:59 PM

Gimpy, after further investigating I do not believe the stock pistons can be lightened much, the wrist pin boss is only .200" thick and probably needs the material that I was going to recommend removing. However you should be able to remove the bottom .200 of the piston skirts but the loss in weight is probably only a gram or two. If you decide to shave that off make sure to chamfer any edges after your done.

gimpy · #30 (**permalink**) 02-24-2010, 05:00 AM

Thanks for looking K6,but I don't think I'll risk rod damage(pressing pins out,back in) for a couple of grams.Am rubbing on piston crowns now,waiting for the new piston,and the cyc. head ect.ect.ect.
Gimpy