Topic: Purple Rain Bill's CB750/900 Turbo 1972

[Medyo Bastos]

Billy, you might want to consider this ~>  http://forums.sohc4.net/index.php?action=dlattach;topic=143926.0;attach=290591;image   

another shot ~>  http://forums.sohc4.net/index.php?action=dlattach;topic=143926.0;attach=295882;image   

[Bill/BentON Racing]

How's the boost retard work? 

[dragracer]

Research a Hobbs pressure switch

[Bill/BentON Racing]

Went looking deep in the batcave! Knew I'd find a carb and a data processor,  1938, Carb unknown Carter! Alright, M Rieck to the rescue!! ,Bill 33.5 intakes, ported, chambers opened up. Nice head or was. 

[scottly]

Did you measure the piston ring end-gap on the surviving cylinders yet? The autopsy isn't complete yet...

[Bill/BentON Racing]

No sir Doctor. ..haha, anything else, did check intake rubbers for a cut ,leak etc, all good. Will measure in a few, working on it now, keep the input coming, we can all learn together. ....at my expense!!!! Haha.Lol  , Bill Can tell you number 4's ring end gap is over the limit!!!

[scottly]

Boost requires a larger gap. Both yours and Johno's failures were in the ring area on the side of the pistons, rather than holes melted into the piston crowns, or melted off plug ground straps, or chipped off porcelain on the electrode that are the normal symptoms of detonation.

[madmtnmotors]

Boost requires a larger gap. Both yours and Johno's failures were in the ring area on the side of the pistons, rather than holes melted into the piston crowns, or melted off plug ground straps, or chipped off porcelain on the electrode that are the normal symptoms of detonation.

Very interesting....

[scottly]

If the ring gap is insufficient, the ring can expand under high temps until it presses so firmly against the cylinder wall that it seizes, destroying the ring lands in the piston.

[Bill/BentON Racing]

Which could have happened,  cause, like you said, usual detonation, flame fronts colliding is not on the edge. Also why, 4 and not another especially 1 since it and 4 are leaner normally. Questions to be answered we hope. Talked with Mike today,  we got a plan!  Off to measure .

[scottly]

 

[Bill/BentON Racing]

Number 1 had .014 top ring, .018 second one. But what did 4 have?  , Bill

[scottly]

After Trey got done with it, #4 could be measured with a ruler. What is the bore, Bill?

[dragracer]

After Trey got done with it, #4 could be measured with a ruler. What is the bore, Bill?

In Trey's defense, this bike really was not set up for safe guards as to maximum boost. Bill and I have to also take some responsibility for the instructions we failed to give Trey when we told him to ride the bike out on the street to " feel the boost". We should have explained to him to test his launch technique only and not to test the limitations of the bikes top end as there was not a rev limiter on the bike nor did Bill have a clue as to how much boost the wastegate was set for on the bike. Yes, the old heads failed the young buck- we hang our heads in shame. Lol.

[Bill/BentON Racing]

+1. I never saw the tach or boost on my first pass until I crossed the line a winner, damn it felt GOOD, addictive. Yep the old guns knew and told....but did not emphasize, pretty much on my watch, I'll do better next time. , Bill

[NalleyRacing]

Hey I learned a few things too.. And this rebuild actually gives us some insight into the motor that we didnt have before.. But regardless, I still feel terrible that there was so much damage caused. 

Especially to that dang cylinder head.. I mean.. It had purple retainers and even said Bill on the bottom!!

[Jim F]

Call rick Stetson or terry Kizer
Both these guys helped me set up everything for boost
I picked the MSD mc-4 because of the almost un-limited
Programming of boost retard that is in the softwear
You have to get the boost sensor (obviously) and then your set
Mine is set on a very safe set up 8:1 Pistons c16 fuel and 1.5 degrees
Of timing after 2lbs up to 12 lbs for a total of 15 degrees with a static timing at 35 degress
Mine will be on the dyno next Saturday with the lap top hooked up
To watch the retard kick in and as long as the AF stay at 12.1 then
It should pull good to 12 lbs of boost.
If it gets rich then put a little timing back into it
Yes the MC-4s are expensive but it's worth the money to keep
Everything in control
My 2 cents worth
Call terry and or Rick and they can tell you about set ups for these systems
Good luck
Jim
and yes I do run a fuel pump
3 lbs is all the needle/seats can handle but its seen red line many a times
and never dropped below 2.5. will see when we turn on the boost

[scottly]

Here are Wiseco's guidelines for ring gaps:

[Bill/BentON Racing]

900cc.  Wiseco instructions won't open up for me, Bill

[754]

How does that rod feel for play?

[TurboD]

Bill your ring end gap is on the minimal side, but I don't see it as being a problem or your problem. I have seen many get away with far less.

That said. I am going to quote myself from my earlier post. This is the number one thing I would look at for the cause....

My Quote
"Bill if you do not have a fuel pump on the bike, this is the problem that caused the meltdown. There is no way that a single float bowl, single needle and seat with gravity feed will keep up with anything over a few pounds of boost. A lot of pressure is not needed, 2-2.5 lbs of fuel pressure will keep up. Too much pressure and the needle and seat cannot deal with it."

[Bill/BentON Racing]

Well it'll definitely have a pump and regulator.  I'll start at 3 and go from there.

[scottly]

900cc.  Wiseco instructions won't open up for me, Bill

Anyone else having a problem with the Wiseco pdf?
900cc would be about 67.25 mm, so .014" would be OK for a "street-moderate turbo/nitrous" application, but I think the amount of boost was a wee bit more than "moderate". Boost, timing, mixture, and the demands of drag racing all may have contributed to the failure, and we will never know what the gap was on the failed cylinder. Just be aware of the gaps on the next motor..

[Bill/BentON Racing]

Thanks, good advice, I always check gaps, even though std rings usually ok. I never had the top end off this one, just replaced trans gears etc. We will check and we will try again!! K, Bill

[hotdog]

Went looking deep in the batcave! Knew I'd find a carb and a data processor,  1938, Carb unknown Carter! Alright, M Rieck to the rescue!! ,Bill 33.5 intakes, ported, chambers opened up. Nice head or was. 

How far did it go up the pipe Billy. ?. don't forget to check turbine wheel.