Early Coolant Seal Failure w/ Used Irons (Lapped Only)
03-27-11, 02:49 PM
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Early Coolant Seal Failure w/ Used Irons (Lapped Only)
Seems common to see these engines rebuilt with irons that are lapped only, as opposed to grinding, lapping, and re-nitriding to factory spec. The (cheaper) approach of lapping irons only seems to lead to early coolant seal failure (or at least that's my theory) because the opposing surfaces are not exactly flush, and lack of nitride coating leads to warping of the coolant lands.
From Yawpower.com:
From Yawpower.com:
Housings are ground flat, and then lightly lapped to provide a minimum surface finish of 15rms measured across the grain. We prefer grinding to lapping for two reasons:
1. Grinding insures that the opposing surfaces remain parallel. Lapping provides a flat surface, but does not have a mechanical reference to the opposing surface. Grinding involves mounting the housing to an electromagnet which is parallel to the grinding wheel travel so that dimensional accuracy is maintained.
2. A housing that is lapped mirror smooth will have little or no oil retention. This is clearly illustrated when applying assembly lube to a mirror finished housing. Rather than spreading evenly across the surface, the lube will bead up much like water on a freshly waxed car. Our process leaves some grain intact to hold oil on the surface, and the light finish lap flattens the top of the peaks insuring that the seals have a smooth finish to ride on. This approach is more time consuming, and so more expensive, but has proven to us to give the best housing and seal wear, along with a quick break in period."
1. Grinding insures that the opposing surfaces remain parallel. Lapping provides a flat surface, but does not have a mechanical reference to the opposing surface. Grinding involves mounting the housing to an electromagnet which is parallel to the grinding wheel travel so that dimensional accuracy is maintained.
2. A housing that is lapped mirror smooth will have little or no oil retention. This is clearly illustrated when applying assembly lube to a mirror finished housing. Rather than spreading evenly across the surface, the lube will bead up much like water on a freshly waxed car. Our process leaves some grain intact to hold oil on the surface, and the light finish lap flattens the top of the peaks insuring that the seals have a smooth finish to ride on. This approach is more time consuming, and so more expensive, but has proven to us to give the best housing and seal wear, along with a quick break in period."
03-27-11, 02:55 PM
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Why aren't more shops offering this type of service?
http://www.chipsmotorsports.com/serv...d-re-nitriding
http://www.chipsmotorsports.com/serv...d-re-nitriding
03-28-11, 04:29 AM
#3
Simply, it adds to a rebuild cost which nobody wants. Almost all rebuilders don't even do lapping. It's only really worth doing if you have special porting you don't want to lose or have to re-port. Otherwise, why bother? For the cost, just get new side housings. Or get a new engine for $3600-$3800 from mazda apparently?
thewird
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03-28-11, 05:29 AM
#4
Nitriding is a hardening process. If anything it reduces dimensional quality, it does not improve it. Likewise the argument against lapping can be resolved with a quick burnish of a flapper wheel.
By the time you've properly reground and nitrided a housing you can probably buy a new one.
In any case there are no wrong answers if you're using good parts.
David
By the time you've properly reground and nitrided a housing you can probably buy a new one.
In any case there are no wrong answers if you're using good parts.
David
03-28-11, 09:19 AM
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$480 to re-condition for all three irons - not bad - I think the price new is about $350/ea?
My main point was the nitriding/hardening - when that is stripped off by lapping, warping of the coolant lands seems more likely.
Let's face it, rebuilds very rarely match factory engine longevity, even at similar boost levels.
My main point was the nitriding/hardening - when that is stripped off by lapping, warping of the coolant lands seems more likely.
Let's face it, rebuilds very rarely match factory engine longevity, even at similar boost levels.
03-28-11, 02:30 PM
#6
I always see excessive wear on irons that have been lapped. Often times when I receive these core engines I dont get the full story of who lapped them and if they were re-nitrited. In my opinion, either the irons are within spec or trashed. While new/perfect irons are great, you would be shocked how little compression is lost due to iron wear. If you have nice low mileage rotor housings, and properly clearanced seals you can make great compression with less than desirable irons.
03-28-11, 03:37 PM
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I think your statement points to the number of shoddy rebuilds out there, slapped together with worn parts either by supposed professionals or shade-tree mechanics.
Anyone can assemble a rotary, properly building one is a different story
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03-28-11, 04:01 PM
#8
Ive seen some funny stuff over the years with remans:One ported one non ported housing, 2 side seal springs crammed into one side seal slot, NA rotor in one housing and turbo rotor in the other. This doesnt even touch on the dealerships install botches over the years. However, for the most part, remans were a great priced alternative to rebuild shops.
03-28-11, 04:05 PM
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My experience with a reman engine was a disaster, while my original factory motor was bulletproof for 65k until I decided to push it with boost creep and marginal fuel (usual issues)
03-28-11, 07:00 PM
#10
Nagao, Present Status and Future View of Rotary Engines, 1986
As you would expect, far more gases escape at the apex seal and rotor housings than at the side seal and presumably the side housings. You can see how much work Mazda did over the years playing around with the shape and design of the small triangle apex seal piece as well as the corner seal. They didn't really mess with the side seals much until they redesigned it for the side exhaust ports on the Renesis.
03-28-11, 07:12 PM
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I'm more interested in coolant seal failure and overall longevity. Anyone can throw together a motor with out-of-spec irons that puts out decent compression numbers (for awhile).
I asked Howard to start a thread on why coolant seals fail, perhaps he will do that...ticks me off because otherwise my motor is flawless, essentially zero wear on the rotor housings, rotors have very little carbon, etc
I asked Howard to start a thread on why coolant seals fail, perhaps he will do that...ticks me off because otherwise my motor is flawless, essentially zero wear on the rotor housings, rotors have very little carbon, etc
03-28-11, 07:19 PM
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Howard doesnt need to start a thread, it's not overly complicated to understand.
Change your coolant every 12-18 months, run 50/50 with distilled water, and don't overheat. Done.
Change your coolant every 12-18 months, run 50/50 with distilled water, and don't overheat. Done.
I see what you did there.
03-28-11, 09:13 PM
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He said he was interested in such a thread
I did all that (and I don't think it's quite that simple)....still developed a very small leak (took about eight hours to fail a coolant seal pressure check)
Change your coolant every 12-18 months, run 50/50 with distilled water, and don't overheat.
Last edited by yzf-r1; 03-28-11 at 09:17 PM.
03-28-11, 09:16 PM
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Yes, they were aftermarket, but all were perfect except for one. One of the coolant lands seemed to be a bit warped in one spot, and the corresponding seal was clearly cooked. Maybe I'll try to get a pic...
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