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At 500 miles and did an oil change, new plugs and coils (left my old ones in to break-in) and did a compression test with a TR-01 test I built from the instructables site.
Here are the tester setup and the numbers: Used a 200 psi transducer and the base program for the TR-01 project. I also verified the calibration with a pressure regulator and another pressure gauge. So three matching gauges. I think the numbers are great! Not stellar according to Mazda but only 500 miles so maybe they'll get even better!
well I’m glad you went and found the information. It was only intended with sincere purpose.
the side seal interface at the corner seal isn’t a wide sealing surface, but if you can find a copy of the original SAE paper you’ll see that the Renesis concept is designed around small clearance differences to minimize exhaust gas leakage. Except they didn’t bother with that one so much.
the difference is that the flat end is close to the round corner seal at one brief point with more open ends. It behaves like an orifice just squeezing it that closest point allowing flow to get there easier.
but the curved profile makes it a longer, narrow channel over the full seal width, which is going to increase flow resistance, particularly as rpm and gas pressure increases.
When I did my rebuild combining the irons with the rotating assembly of two different ~125k mile engines there is a sweet balance that has to be made when cutting your own seals. I'm going to link my thread about my whole ordeal, but try to sum up what I learned here.
So to get my 125k mile rotors and irons to make good compression I had to get the sides as tight as possible without binding one of the corners when hot. Of course if you go too tight, all the seals may return when you press them on the table like everyone says to check. Even if you press them all down together, it could still be too tight and bind when the engine gets hot and expands. From research people were saying if you slide a side seal against one corner and then measure the tolerance of one of the sides it should measure 0.002in to 0.006in. Some people were even saying to run 0 gap, which i just can't fathom why/how that would work.
From the compression tester kit: 120+psi = Excellent 110+psi = Very good 100+psi = good 85+psi = Fair, but falling below mazda's standards 80-psi = Hot start issues and lack of power
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I found through hard testing of building, installing, and running an engine with 0.004-0.006in gap seals was lacking compression, could start cold but would barely idle hot and not hotstart. This build gave me 85psi@250rpm cold and 65psi@250rpm hot....not good, the 85 psi cold could get me to start...barely, but then would die on its own at running temp/idle
Upon rebuilding a month later another test had the gap with new seals around 0.001in (which all could be pressed in at the same time on the bench and return btw) This engine had similar issues idling and hot starting. This build had a similar 85psi@250rpm reading as before
The third (final/current) build which is between 0.0015in and 0.002in gave me decent/good compression around 105psi@250rpm cold and 100psi@250rpm hot. @250miles breakin Still issues with one corner seal binding.
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When my current/good rebuild did start, it was near instant. Fast enough that I couldn't let go of the key quick enough. No idle issues. No hot start issues. If you don't see this result, first thing to doubt is the engine build.......then double check over the reinstall.....then doubt the engine again. Knowing I would eventually make use of things like a new starter/fuel injectors/plugs/maf/plugs/vacuumLines/plugs/grounds/fuelPump/plugs/battery/belts You name it, I tried it, nothing changed the fact that the compression was low. I couldn't recommend buying/building a compression tester more. The ~300$ is well worth saving all the money spent on the above......granted at this point I almost have a new car.
Now the only real solid thing to learn from this is that there is a balance between too tight and too loose of a tolerance here. Ideally we want it as tight as possible without binding. Going with a gap of 0.002into 0.0025in is probably the safest bet for most engines. I went tighter with the notion of my 125kmile rotors are not in the best of shape and the tight gap could make up for some of that compression loss. Other than the rotors, the irons I hand lapped using a large granite slate with a lapping compound paste. Finding a reliable shop to professionally machine lap my irons might get better compression. On my current build with the 0.0015in-0.002in tolerance I believe I am still having issues with a corner seal binding when hot and losing almost 10psi across two chambers.....hoping the breakin resolves this. Currently @600miles breakin so far, only issues I have other than that I believe are fuel/computer related.
I want to say having new rotors or even 60kmile rotors could very well see a different result in where that balancing point of how tight of a gap can you get with no binding is. So all my testing to find that perfect value may be near invalid for whatever your case may be. Good luck regardless :D
if it doesn’t have 120+ psi with a warm engine after a short run in, it never will.
you need new rotors; and if the funds or rule allowances permit, machined for deeper RX7 apex seals which preferably would be Iannetti ceramic for an NA engine, new rotor housings, and resurfaced irons if within tolerance. From there you can get several rebuilds reusing those parts, short of some catastrophic failure tearing things up which is unlikely if it’s built and maintained properly.
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Had a major setback, 2020 was a real suck-it year so no surprise. The housings I sent out to have resurfaced and renitrided look like they never got nitrided. First time I ever got this service done so I really didn't check the housings for hardness. The rebuild only lasted 1000 miles and the compression dropped and gave me hot-start issues. Anyway, the place that did them said they were done right but they still offered to do them again for no charge... I got them back about 3 weeks ago and tested them for hardness this time, all looks good now. My old sideseals were trashed and I really didn't like just using the stock seals from Mazda on the last rebuild anyway, so I got out my new set of un-cut sideseals and setup a jig to cut the corner-seal contour in them. I have some pics below to show the trashed housings and the new ones and also my jig and the nice sideseal fit I got using it.
Only 1000 miles!! What a waste of time putting this together. Live and learn... Goes to show you how important the renitriding is.
Sent them back and got them all resurfaced and looks like they actually hardened them this time...
How's that for a nice contour! This is a picture of one of my actual side seals. I clearanced them all to about .0025" using the jig I made.
Just a drill press and a couple of clamps to help guide the seal to the gridding stone. (this pic shows a course sanding bit but I changed it out for a stone to get a finer finish). I got the angle set using a few old sideseals to test and then cut the new seals.
Just a pic of my work station. Nice wooden welding bench...
Went off of this guide for my standard clearances.
I'll post the compression number once it's running...again!
a lot of race builders don’t re-nitride them. In fact my builder said not to bother fwiw (same for all the fancy coatings, he’s tried them all), but maybe it just depends on how much is removed to start with. Regardless, that’s generally a long term/high mileage difference.
for what the pic shows to happen in such a short period might suggest a different issue was the cause; seems more like they were running dry without oil imo
Looks good now. I used some oil and a orbital sander with a 320 grit disc and it made my old irons look new without removing too much material. They have held up for 15,000 miles so far.
I found that by time you machine the irons and re-nitride your half way to a brand new set.
a lot of race builders don’t re-nitride them. In fact my builder said not to bother fwiw (same for all the fancy coatings, he’s tried them all), but maybe it just depends on how much is removed to start with. Regardless, that’s generally a long term/high mileage difference.
Next time I do a rebuild I think I'll just buy a reman motor and disassemble it for the parts to put it back together the way I want it. At least that way I'll have all new parts like the housings and seals. This rebuild ended up costing me a lot more after I added everything up, especially with the housing screwup. It also looks like the place that did the housings gave me different housings as they came back with exhaust studs in two out of the three and I pulled all of the studs before I sent them. I think they already cut too much off of the first set and then with the scratches in them they were shot. But no charge to me so I'm ok with that, just the time to get this back on the road is ridicules.
Originally Posted by TeamRX8
for what the pic shows to happen in such a short period might suggest a different issue was the cause; seems more like they were running dry without oil imo
I was premixing the whole time and it did look like the oil lines filled up with oil pretty fast (I have new lines I made from material I researched so they are very clear to see oil in them. Do you know if there's some way to prime them before starting or if just all of the oil from the build and premixing is enough?
there’s no guarantee on new parts with a reman, so maybe
have you checked reman prices lately? Because I looked the other day and the near wholesale price for Motorsport members is quite a bit higher than what it was retailing for previously. So maybe they do have those parts new and the price reflects that. I might suggest just paying the extra for a Pettit OTS engine, which has all new parts that’s hand built and blueprinted.
I forgot that they don’t accept cores. So if you order something with a core, the core cost gets added to it. That puts it fairly close to the new engine cost. Kind of makes sense.
Looking at the plate wear & pattern though, seems like a significant mechanical contact/scraping issue rather than material hardness. What did the rotor tips and sides look like?
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I forgot that they don’t accept cores. So if you order something with a core, the core cost gets added to it. That puts it fairly close to the new engine cost. Kind of makes sense.
Looking at the plate wear & pattern though, seems like a significant mechanical contact/scraping issue rather than material hardness. What did the rotor tips and sides look like?
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With that in mind for the rebuild cost I think I'll just convert it to a 13B with a turbo next time. Living in CA I'll just swap a Renesis in for smog every two years.
No I'm sure it was the plates, the material seamed to scratch easily but I just ignored it because the shop I got them from told me it was just a coating from the heating process. The side seals and corner seals looked a scratched but they didn't show any wear as far as height when I measured them they were still the same height as new. Look at the pics my previous post that have a close-up of the rotor with side and corner seal and that's what the rest of the rotor tips and seals looked like. I rebuilt this motor before and when I took it apart after my first rebuild the side housings looked normal, no scratches just normal wear. Just got trashed after getting the housings machined...
The newest rebuild is back together and I'm putting it in tomorrow so we'll see how it goes this time.
09-30-2020, 02:45 PM
