dyno dilemma

VMAX  Forum

Help Support VMAX Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Fire-medic

Well-Known Member
Staff member
Moderator
Joined
Mar 25, 2011
Messages
14,888
Reaction score
3,976
Location
Miami Florida
I had a dyno done by a reputable shop and this is the result. It was a Dynojet 250. I watched it being done, 3 pulls, none of which were excessively long in duration. I was outside the sound-enclosure and did have a view of the electronic screen where the rpm's were graphically-displayed. It looked to me like the pulls went beyond 10K when they got into whatever gear they use, which I would suppose is probably 4th, as I believe that is 1:1. I think they over-revved it and smoked the rod bearing & crank on the runs. I videotaped the runs and thought I had a clear view of the computer tach simulated screen, but in playback, it is too-indistinct to show the rpm's they ran the engine to.

The engine is a totally-stock one. My bike is a 1992. I got on the bike after they took it off the dyno and parked it outside the shop. I started it up and began riding home, a distance of ~3 mi. After about 1 mi., the engine began making "rod noises." It still ran, but I figured at that point, the damage was done, so I rode it the rest of the way home.

I tore it out of the frame and took it to my friend's shop, 'Under Pressure," Dania Beach FL, where the owner Steve confirmed the #3 rod and the crank is toast. The adjoining #4 rod is not much better, but it doesn't have the ~2 MM of big-end play the #3 rod does on the crank journal. Notice the color in the area of the mortal wound.

Sadly, I doubt there is amy recourse I have against the dyno operator, as he will claim the engine was already 'hanging by a thread,' and that the dyno was the last-gasp by a bad engine. I haven't even approached them about it. Caveat emptor!

My intent was to get a baseline for some bolt-ons I was about to make, a full set of carbs Dynojet Stage 7-kitted and including K&N pods for the intake and a barely-used UFO silver-coated 4/1 w/the shorty slash-cut baffle. I wanted to be able to say, "this is what these were worth on my bike, your results may vary!"

The engine was running fine before this, no problems starting or running, I hadn't synched the carbs yet but I believe they were reasonably-close. It carbureted smoothly and cleanly, and would pull to 9K+ w/no issues whatsoever, though I wasn't in the habit of running it to redline every time I got aboard. I am also not one to make drag-racing starts and have never been to the strip to run it. So, if I had to say, it received enthusiastic use w/o being abused or raced. I didn't speed-shift. But what happened is the crank probably had a rod big-end failure due to over-revving and oil failure.

Before my mechanic disassembled it, he told me, "it's going to be #3 bearing for the connecting rod/crank." Sure-enough, it was.

So, leave well-enough alone, is my advice, I would probably be riding using the same engine today if I hadn't had the dyno test done. Do I want to lay the blame on the dyno operator? I would like to, but unfortunately I have no proof they over-revved it. :confused2::bang head::bang head::confused2::damn angry::damn angry::confused2:
 

Attachments

  • #3 rod.jpg
    #3 rod.jpg
    62 KB · Views: 117
  • #3 rod close-up.jpg
    #3 rod close-up.jpg
    47.4 KB · Views: 109
That does all suck! what kinda HP were you making?, that may be an indication of if the motor was weak or not? Best of luck with the rebuild and Mods.
 
You'll have to prove that they did the harm, did you sign a waiver? If you signed one most likely all bets are off. It really sucks and I hope you get back up and running soon.
 
No need to run a stock Gen 1 past 9 Grand. Everything is dropping off by then... Still, 10,000 isn't destructive on a good motor but more is not good.
Sorry to hear this happened.. Your Dyno sheet should show the RPM they ran....:confused2:
 
Shitty deal for sure. Especially considering all the work to get it going.

I can't see a quick run up to 10-10.5K causing catastrophe.
Any signs of a displaced o-ring on the oil elbow? Just curious.
 
Jeez man, I'm sorry, I do know how that feels and it ain't good......:bang head:

Bet you're buddies at UnderPressure are going to guide you through an awesome rebuild process tho'

Just sleep on it and think about it...that's what God made tomorrows for.....
 
A little over 10k isn't normally going to kill it. It needed to be warmed up a good amount before the pulls which wasn't discussed. I've consistently run mine over 11k but as noted much over 9k isn't normally giving any more power.

Odds are the block is also damaged. Need to check and verify it before spending the money to repair it. Look at the crank thrust surfaces. If you can see and feel where the crank rides on the surfaces then it's going to need repaired or replaced.

We do have some good used engines (complete or needing transmissions which you could move over from yours) as well as good core cranks/rod assemblies.

Sean
 
Bugger. That sucks.
But... now you get to do a ground up build! :biglaugh:

For accuracy's sake, if anyone else has an engine problem, you need to shut it down ASAP! Minimise risk of black damage etc.
 
Bugger. That sucks.
But... now you get to do a ground up build! :biglaugh:

For accuracy's sake, if anyone else has an engine problem, you need to shut it down ASAP! Minimise risk of black damage etc.


I've made that mistake, was on an old Yamaha snowmobile. It was a tired old girl, something like 8000 miles of enthusiastic use(which is already a long life by 80's 2 stroke standards). Was running it hard and it smoked a piston and lost all compression on one cylinder. It still ran, and we didn't feel like towing it 30 miles back, so I just said fuggit and ran it home on 1 cylinder figuring "the damage is done, can't get worse".

What could have been a simple top end ended up ruining the crank since bits of molten metal from the hole in the piston went down and found their way into the crank journals. As I got almost back it was REALLY losing power, more than just running on 1 cylinder. Got it on the trailer shut it down, 5 min later it was locked up. Granted....a 2 stroke sled motor is 10x easier to rebuild than a Max mill.

On the other hand, we took the opportunity to violate that poor old 485...punched out, new crank, shaved down the head. You need 2 hands to pull the cord it's got so much compression and that old Phazer friggen cooks now, and it's been running strong for like 4 years now. Total sleeper.

If you suspect engine damage, shut it down asap, short of some critical emergency. You CAN make it worse.

I've had mine over 10k once or twice, both times unintentional. It's survived, but I really try to be careful with that. I lowered the shift light setting to 9k, by the time I see it and react it's already at 9500 or past.

Sucks dude, but see it as an opportunity for full 1570 build! If my motor ever takes a dump(knock knock), I'll put the money into a full motor build rather than buy a new bike. Till then, it's still going strong creeping up on 30k. How many miles were on your mill?
 
Thanks to all who have made suggestions, I will follow-up later Wed. after work.
 
after work won't probably be for another 6 hours from now i'd imagine
 
OK, here you go.

The engine was to operating temp as I rode it to the shop and they did the pulls within about 10 min. from me getting there. They pulled three times I believe, but I only have sheets of two. This is the best one, the other was a similar profile and was <1% different in max. h.p.

No torque, no rpm listed.

While I would like to spend the $$$ for a 1500+ cc engine, that is not within the budget right now. I will settle for having my engine back together and running reliably. I am going to replace the stock intake and exhaust in the future, I have the parts, but for now I just want to ride it again, stock.

Actually, if I was tempted to do a 1500 cc engine, I think I would sell mine, fixed, and put the engine mod $$$ and the bike sale $ towards a Gen.II. That would probably get me halfway towards what they are going for now.

Realistically, I am just going to repair what I have and enjoy it for awhile. I am open to advice, so if you want to weigh-in with options and costs, please do.

If the print is too-small, the h.p. output was 109.23.
 

Attachments

  • dyno 1-13-12.01.jpg
    dyno 1-13-12.01.jpg
    37.6 KB · Views: 86
It's still going to be cheaper to get a good used engine.

Sean
 
IMO, I don't see any sign of over-revving.
Calculated at 9500rpm in 4th gear would net a Stock geared Vmax a top speed around 129mph @ 9500 and 137 @ 10k (Speed spreadsheet) , and the looks of the curve on your printout, it drops off after about 135ish.
Maybe is wasn't warmed up properly before the pulls and the O-ring blew. :confused2:
 
Back
Top