Gen II Valve Springs/Retainers/Cam Chain Experiences?

Matt Graham

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Hayabusa Gurus,

I run a Gen II Busa in my Radical SR3 road racing car. The engine is bone stock except for a dry sump setup (scavenge pump replaces the water pump, use electric water pump) and larger oil and water rads.

This past season was my first using the Gen II engine, and in terms of power, drive-ability, etc, I am very pleased. That being said, at the last outing of the season, the cam chain broke bending several valves. Upon further inspection it appears that some of the valves might have started to pull through the retainers, and that this may have caused the valves to float, causing the cam chain failure.

I searched several times and didn't find much information on the stock Gen II valve springs, retainers and cam chain, so if it's already been discussed, please forgive me (and please point me to the discussion).

So what say the experts? Should I treat this as an isolated failure? Will the stock springs/retainers/cam chain hold up to my abuse of a stock engine or should I invest in some heavy duty parts? I really prefer to NOT open the stock engine and start messing around in there, but I also don't want to drive around a ticking time bomb.

Thanks in advance.

-Matt

PS - A pic of the car

mosport.jpg
 
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The stock automatic cam chain tensioner may have failed or backed off, causing the chain to break. That would be my guess. Yes, the Ti valves in the Gen II are less tough, and the springs that come in the Gen II are very very light. Since you need to replace them anyway, its a moot point if the valves caused the problem. You won't have a problem with SS ferrea Valves and 55# springs and a manual chain adjustment.
 
Draco,

Thanks for the insight. I had planned to move to the manual cam chain adjuster.

If I swap out for a new stock engine, what needs to be touched in the head? Retainers? Springs? Valves? All three?

Thanks,
Matt
 
I preface the advice by saying that I don't do this professionally, but I have made my fair share of mistakes along the way...

Remove and completely disassemble head. Check for cracks between the seats and plug area.

Check cams for brinelling on back side of lobe. If you were floating valves, its the back side that breaks up on you. Now bolt cams back into head and spin them to make sure they are not binding in bearings. If you bend the valves badly, you can also have bent the cams or damaged the cap.

Check valve guides. Make sure none of them got pushed in during the hit. Repair as necessary.

The Ti valves and OEM springs can probably be made to work for endurance applications, but you are on your own. What I do know that works is Ferrea SS valves with 55 to 60 lb springs. In theory this may cost you a HP or so, but in practice, you get most of the resistance back on the back side of the cam lobe. After you do your port clean up (exhaust side in particular is bad) then lap your valves in and vacuum check them. The heavier springs are also double springs, so they resist harmonics and have some level of damping from the slight rubbing of the two springs.

Since you mentioned your keepers were slipping, they probably lost there edge. I would replace them as well as the seals. Obvious stuff. You can probably get away with the OEM retainers. They are the same as used on the GenI.

Replace the chain with Tsubaki and tensioiner with manual tensioner. Get an oem head gasket.

Now the bad news... because I don't know how hard you bend the valves. The impact may have likely damaged rod bearings. Worst case scenario is the the big ends could be out of round, the rods could be bent, the pistons may be cracked, and even the crank could be bent. A good machinist can fix all of the above, but you may want to check for these conditions. You will need to remove the bottom of the engine anyway to put the cam chain on, so the right thing to do is remove the rods and go through them meticulously for twist and bend.

Good luck, and let us know how you make out.
 
Draco,

Thanks again for the insight.

In terms of the questions for the stock components, I'm not really interested so much in reusing anything from the engine on which the chain snapped, but more trying to determine if the spare engine (also completely bone stock) should get some preventative upgrades.

Thanks again!

-Matt
 
Matt,
Sorry I didn't (try hard enough to) understand your objective. If your just prepping a spare engine, You may still consider swapping the Ti valves. Not a lot of expertise out there for endurance applications. I measured 23 - 27 lbs of spring pressure after only 1k miles. In theory you might get away with just shimming the springs up to some slightly higher number than stock. ?? . In the car world, there are people using Ti valves all the time, but the Busa spring / Ti valve combination has not been as robust. I would go with stainless.

The other mods that you may (or may not) benefit from are oiling mods. Again, us bike guys don't have to worry about lateral Gs like you, but putting in a baffle and increasing the pressure of the relief valve in the main oil galley is always recommended. There are also many of us that block off or restrict certain oil passages to push more flow to the rods. Lots of games that can be played.

Great looking car by the way.
 
Draco,

Thanks again for the continued advice. I think I'm OK on oiling, as I run a dry sump system. Data logging (fully instrumented engine) shows good solid oil pressure under all conditions (cornering, accelerating, braking). Ran Gen I engines for several years in the same car and never had an oiling related failure (or any failures that weren't directly related to user stupidity/external stuff).

-Matt
 
Hi Matt.

I have a spare engine here from a crashed bike (B-King) that has a cracked lug on the head. Is your head casting OK and would you sell it?

FYI, I've been using a GenII for a season and a half with several track-days and test days between without any issues.

I too am dry-sumped.

Cheers
 
Chip,

I sold the entire engine to a local speed shop about 2 weeks after the cam chain broke.

Thanks for the info on your experiences.

-Matt
 
Most of the Radicals come from the factory with our roller cam chain conversion.

If yours has the hy-vo style chain, you might consider replacing it. HAYBUSAZONE ZONE - Cams and Cam Sprockets

If you want to keep using the Ti valves, get our 47 lb spring kit. They have a higher spring rate than stock, yet work well with the ti valves. HAYABUSAZONE - Valve Springs and Retainers

And of course the manual tensioner. HAYABUSAZONE

Be sure to remove the clutch basket assembly after each outing and make sure it is not self destructing.

E-mail me at jay@aperaceparts.com if you have any more questions.

Jay
 
Jay, Thanks for the info. I've already been talking to the folks at Radical Performance Engines (formerly PowerTec) as well as dome other Sports Racer engine builders, and all of the information is a great asset.

I've not heard, nor ever experienced any clutch basket issues. What should I be looking for?

As for more info on the car, check out Home - Radical Sportscars

-Matt
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