I recently purchased a hayabusa local to myself after getting faffed around on ebay by a seller android31 (beware of seller)!

I bought several items for the engine from Carl at extreme engines, which advised me on the phone to buy cam cap bolts for it as they stretch and break, kinda took this a sales pitch to start but though at £15 wot do I have to loose as piece of mind?

So I received all the items started working my way through the engine items today and came to the cam cap bolts, replaced them 1 by 1 and found that only 2 weren't stretched and swollend 2 were that stretched that the were no longer threaded in the middle and was EXTREMELY lucky to remove in 1 piece, 2 in the centre on inlet cam started to pull threads on the head which I had to repair today,

I reckon that if I had of left the bolts I'd have been exceptionally lucky to avoid a engine failure, so please take this as a word of warning, I have built 100's of engine's when I worked at 1 of the uk's top tuning centre's with a 4wd rolling road and never seen this in my life on cam cap bolts!!

Extreme engines were a absolute god send to me in this build!! Saved me a engine

I assume a complete strip down is required to get at those bolts?

No just the coil packs removed, the rocker cover removed, change them 1 at a time so you doing need to reset cam timing etc, when you come to cam chain end you need to remove cam chain guide and refit it,

2 spinners difficulty on the Haynes manual guide lol

Ive just rebuilt my engine and didnt change these, haven't yet driven it so now ive read this i think ill pop the rocker cover off and replace them.

They all made the correct torque when i fitted them though. Better to be safe then sorry though i suppose!

John

I just thought it was worth mentioning, I have built numerous Hayabusa and other Suzuki engines and never had any issues with cam cap bolts. However if you read the Suzuki service manual it will tell you that the specified torque figure is just 10 NM or 7 ft/lbs. I have had experience with these being over tightened by mechanics and home builders and this is the reason why the bolts stretch or strip the threads inside the cylinder head. Pay attention to the torque figures and you will not need to replace them on a rebuild. There is also no mention of the bolts being stretch bolts and only used once.

Glad you posted this Mike. First off I couldn't see why a stretch bolt would be used for this, and second how could a bolt be tightend up enough in an alloy head to stretch it? Surely the alloy thread would give before the bolt?

At least I won't need to check mine now ;-)

This is entirely up to the individual, I'm giving my experience of wot I found going on the advice of a reputable engine builder on the hill climb scene.

If u don't believe this that's cool, I was intending on taking pictures of this just haven't had time.

The only advice I can give is I took advice from extreme engines and proved to be correct in my case, if u don't want to take the advice that's upto u?
I'd rather waste £15 for piece of mind than cost myself a motor

Chill out Mike!! I never said I disbelieved anyone and I certainly don't disrespect what others post. I was merely making the point that I could not see or understand how the bolts could have stretched when installed into an alloy head.

No harm ment by my comments, I also understand wot u r saying, I'm the same respect when you torque the cam cap bolt u are adding stress to it, by such a hard reving engine compared to a car, there will be stress in the engine at places different to a car, the cam cap bolts imo are one of them, most tuned cars require arp rod bolts and normally main bolts at the same time.

Different engines have different needs, yes I c the logic in how can this happen my answer is I don't know but it does lol

Changed mine out yesterday, although after talking to jack at holeshot they aren't stretch bolts.

Found one where the thread had become deformed.

All were torqued up to 10nm as per the build manual.

Something to keep an eye out for. All mine were original Suzuki items.

John

[Edited on 1/5/14 by jwhatley]

with such a low torque I doubt this has anything to do with very high stress in the bolts - if the cam caps had that much load then the bolts would need to be pre-tensioned against it

its more likely something to do with the repetitive lower stresses that would be easily handled by the same bolt for short periods - creep is one mode of failure when they slowly stretch in this sort of way

[Edited on 2/5/2014 by mcerd1]