OS 21VZ-B(P) V-Spec 20 gallons Long Term Test
Photos: Senol Sarihan
This is the story of my OS .21 V-Spec (blue head) engine which I had bought in May 2007. It propelled my Hellfire SS truggy during the 2007 season and my Jammin X1-CR Pro Buggy in 2008. After burning 20+ US gallons (76 litres) of fuel, I assumed that it was finally at the end of its useful life but the engine proved me wrong. It is now propelling my Thunder Tiger ER-1 Rally car and it appears to be capable of doing so for a long time.
Break – In
Starting this engine for the first time was a great challenge for my starter box, even if the engine was pre-heated to 200°F (≈ 93°C). I had to loosen the glow plug for being able to crank it and tighten once the engine started. I let it idle at 200°F (≈ 93°C) for two tanks; stopped, cooled down to room temp, pre-heated again and re-started several times for heat cycling.
I also pre-heated it on the track before every start, until the metal to metal pinch near the top dead centre turned out to be a smooth compression with high resistance. This happened at about 1 gallon (≈ 3.8 litres). Thus far, I kept its operating temperature at 200 – 210°F (93 – 99°C) by running it slightly rich and by being relatively gentle with the throttle. I applied more throttle gradually, until I race tuned it.
Operation / Performance
Most of the time, it ran at 220 – 240°F (≈105 – 115°C) with occasional 260°F (127°C) when the tank was empty. I never let it stop due to dry tank at speed, though. I always stopped the car before the last drop and waited for the engine to stop at idle. I applied after run oil after every day of running, even if I knew that I would run it the next day.
I used OS T-2060 SC pipe and OS P3 glow plug all the time. I tried the P6 plug once, in a very hot day, but the engine refused to idle and ran erratically. I always used the largest carb restrictor, the blue one.
Propelling a heavy truggy like the Hellfire SS is rather a .28 engine task than .21. I know that racers tend to prefer .21 for fuel economy but the .21 engines in question must have more bottom-end power with at least the same top end, if not faster. The V-Spec was not purpose built for truggy applications so I kept my expectations at a reasonable level. What mattered for me was its ease of operation and reliability. It was quite satisfactory in this respect. It required only minor changes in tune due to different weather conditions. It started easily. Head temp was always as I stated above. It was not very easy for the V-Spec to accelerate the Hellfire out of slow corners but top speed was quite fast. I set my clutch for relatively high RPM engagement and ran my Hellfire all season without any engine trouble.
It propelled the truck during the entire 2007 season, pitting at every 10 minutes and consuming a total of about 10 US gallons (≈ 38 litres) of Roktan S20 fuel (20% nitro and 15% synthetic lubricant). It was interesting for me to compute that the distance the Hellfire travelled with this fuel was about 1230 km (≈ 764 miles)*. The engine was in tip-top condition at the end of the season. Or, so I thought!
In April 2008, the V-Spec left the Hellfire to an OS .28 ZX. Its new duty was propelling my new Jammin X1- CR Pro buggy. It did so during the 2008 season, pitting at every 9 minutes and consuming another 10+ US gallons of Byron Gen 2 20% Race Formula fuel. The distance the buggy travelled with this fuel was about 1440 km (≈ 895 miles)*. The buggy was naturally much easier for the engine to accelerate. It was a lot quicker out of the turns and top speed was fairly fast. The buggy did not make a difference in head temp.
*Read mileage calculation at the bottom of the page.
Towards the end of the 2008 season, the engine was no longer in tip-top condition. The front bearing was leaking. This means an air leak (dusty air, of course) and a considerable one. It could not hold its tune like it used to be. I was assuming that the engine was at the end of its useful life because; I would not buy a new piston/sleeve set, a new conrod and new bearings. Buying a new engine would cost only a little more than replacing all these parts.
Therefore, my V-Spec became the subject of my experiments. Besides, the engine had faced challenge from two new buggies, one with an RB C6 and the other with an OS .21 Speed Tuned V-Spec (black head). My old engine could not cope with them neither out of the corners nor on the main straight. Experimenting with it appeared to be a good idea to me. I added one head shim and shifted to 30% Byron Race fuel, in addition to increasing the clutch bell size from 13 to 15T. After a short break-in period (not heat cycling, just being easy on the throttle) my buggy became a lot quicker out of the corners and much faster on the straight. Then, I tried a 16T clutch bell. Acceleration suffered. Top speed would be even faster if the straight was longer but the straight was what it is (70 metres or 230 feet). No matter what, the old V-Spec was no match for these higher end engines running with 20% nitro, especially during acceleration on the straight.
Disassembly / Renewal
I disassembled the engine just for taking the piston and conrod for using them as a key ring. It was visible from outside that the front bearing was wrecked. The rubber shield was coming out and I was pushing it back into place! I was certain that the rear bearing would not be in good condition either because dusty air was obviously penetrating into the crankcase through the front bearing. I was a little curious about how the engine still had compression under these conditions, especially when dust was in the crankcase.
I must say that I was not only surprised but also, I felt respect for this engine when I saw its piston/sleeve. So, I decided to revive it. I replaced just its bearings and conrod. It is running great, now. I think the pictures show that the engine deserved this treatment, rather than being thrown away.
Pic 1 and 2 show how far the piston can be pushed up in the sleeve. If they were totally worn out, the piston would reach the top of the sleeve. The distance in the pictures show that the piston/sleeve set still have a lot of useful life. The scratches on the top of the piston are my work! I cleaned the carbon build-up with a sharp tool (but I was careful enough for not scratching the sides of the piston).
Pic 3 shows the piston after 20+ gallons. The conrod is new. I used an OS Speed conrod. Pic 4 and 5 show the condition of the sleeve. If the piston or the sleeve were scratched, they would loose compression and they would not be usable despite the good distance at pictures 1 and 2.
Pic 6 shows the conrod and the bearings that I have replaced while pics 7 and 8 show how much the conrod can play when it is connected to the crankshaft journal. Without play, the conrod would remain between the blue lines. Even new conrods have some play and this amount of play may still be acceptable but if I did not replace it now, I would have to disassemble the engine later, just for replacing the conrod.
Pics 9 and 10 show the new ceramic bearings I have installed. The rear bearing is from TKO and the front one is a double shielded ceramic bearing from Power Save Racing.
Pics 11, 12, 13 and 14 show various components after 20+ gallons. I had removed the back plate a few times. It was not scratched like on pic 14. Worn bearings or conrod must have enabled the bottom of the conrod to contact the back plate. I did not replace it though. Pic 15 shows the actual state of the engine.
It is common knowledge that bearings do not last as long as the other moving components in nitro engines. I should have replaced at least the front bearing at the end of the first season. This would prevent dust penetration into the crankcase so the engine would not be subject to such an abrasion during the second season. Therefore, the rear bearing, the conrod and the piston/sleeve would be in better condition after the second season.
Despite the dust abrasion, it was still not too late for replacing the rear bearing and the conrod and the piston/sleeve were exemplary. I whish I had not neglected the front bearing issue.
After 2670 km (1656 miles) of screaming on different cars and with different fuel, including nitro percentage variations, the V-Spec left the buggy to a Sirio S21 CL7B STI Tuned engine and started its 3rd season, this time on a Thunder Tiger ER-1 Rally car.
The V-Spec is a good performer. However, it is not in the contemporary premiere league where drilled, epoxy filled, coated and balanced crankshafts, ceramic rear bearings, longer strokes, sleeves that are machined and/or hand crafted from outside, etc., are now common practice.
In terms of longevity, its piston/sleeve impressed me, even if its bearings, especially the front one did not. I see no reason why the new ceramic bearings and the new OS Speed conrod wear out before another 10 gallons or so. Will the old piston/sleeve last so much? I don’t know but in view of their actual condition, all I can say is “why not?” Only time will say.
As for value, the V-Spec was in a very good position when I bought it but nowadays, the above mentioned state of the art Italian engines are becoming more and more affordable. Neither a little price reduction of the V-Spec nor the hefty (if not exaggerated) price tag of its “Speed Tuned” version seems to place OS Engines in a favourable position in terms of value for money.
*Method of calculation
10 min pits ≈ 150 ml/10 min
18 sec/lap = 33,33 laps/10 min = 33,33 laps/150 ml.
146 meter laps x 33,33 laps = 4.866 meters / tank = 4.866 meters / 150 ml
3.800 ml (≈ 1 gallon) / 150 ml = 25,33 tanks
25,33 tank x 4.866metres/tank = 123.256 meters/gallon = 123,25 km/gallon
123,25 x 10 gallon = 1.232,5 km
9 min pits ≈ 125 ml /9 min
16,6 sec/lap = 32,53 laps / 9 min = 32,53 laps/125 ml
146 meter laps x 32,53 laps = 4.749 meters/tank = 4.749 meters / 125 ml
3.800 ml (≈ 1 gallon) /125 ml = 30.4 tanks
30,4 tank x 4749 meters/tank = 144.369 meters /gallon = 144,37 km/gallon
144,37 x 10 gallon = 1.443,7 km