Author Topic: Edit: Decided to Rebuild The Top End of other K4 (instead of repair trans) (Read 7191 times)

Drew75 · « **Reply #25 on:** July 13, 2009, 10:36:24 AM »

So as you all know after all that work and effort the bike pops out of second, we tested it on the center stand but not under load - Bill (builder - mechanic) knew right away it was a bend fork selector or busted dog on 2nd. We originally opted to crack the case and fix the transmission and be done but it didn't make a whole lot of sense for an engine with suspect compression on cylinder #1 anyway.

So Bill has two K4 engines on the ready - we picked the best out of the two and decided that a complete top end rebuild would be the smartest move.

Lapping, rings, cleaning, thicker torque bolts, gaskets, rollers etc and paint. So I'm expecting delivery this weekend... hopefully.

Pics attached - Just a little bit more to do.

The new (well old) K4 engine and parts:

MCRider · « **Reply #26 on:** July 13, 2009, 10:53:49 AM »

A fresh stock engine with no head gasket leaks and no jumping out of gear. Just what the Doctor ordered. Just in time for prime riding season. Nice bike!

Bill/BentON Racing · « **Reply #27 on:** July 13, 2009, 04:06:42 PM »

MC,thanks,I got Andrew to post cam chain rubber rollers so people could see what they look like after 30,000m.The guide is is no longer straight and of course worn,Always check and replace as ness.All 3 CR750s with 90hp or more broke their chains,one on the warm up lap,Dick Mann rode the one with 89 hp I believe.I am writing about Daytona 1970.They were the achilles heel and still are,rods second? I am in process of installing studs so I gotta go,somebody wants to ride!Bill Benton

Drew75 · « **Reply #28 on:** July 14, 2009, 07:06:52 AM »

Pics for the post above:

MCRider · « **Reply #29 on:** July 14, 2009, 01:04:29 PM »

Quote from: bellcow54 on July 13, 2009, 04:06:42 PM

MC,thanks,I got Andrew to post cam chain rubber rollers so people could see what they look like after 30,000m.The guide is is no longer straight and of course worn,Always check and replace as ness.All 3 CR750s with 90hp or more broke their chains,one on the warm up lap,Dick Mann rode the one with 89 hp I believe.I am writing about Daytona 1970.They were the achilles heel and still are,rods second? I am in process of installing studs so I gotta go,somebody wants to ride!Bill Benton

Thanks. Those old rollers are much worse than 30k would indicate, either long time use with chain out of adjustment and/or bad oil. Still they get to looking pretty bad in the best of circumstances.The racers chewed them up (and their chains) from high RPM, Daytona CR750s lived above 8000rpm, we live below, so the stock tensioners and chain are fine with proper attention.

Yes on a 90hp CR750 rods could be the next to go. I bent a stock rod on my 750cc road racer which had a yoshimura ported head; cam; 2 ring high compression slipper pistons and Weber carburetors (really) and a bol d'or replica pipe. (similar to Yosh in appearance)

I'm sure I wasn't making 90 hp, but it was pretty good. On the CRs I think they shotpeened the stock rods and that got them through. But they may have had a special rod, a forged aluminum one or the like. There is a monster thread on the CRs "pinned" to the top of the SOHC/4 Forum (this one) worth perusing.

Bill/BentON Racing · « **Reply #30 on:** July 14, 2009, 01:23:37 PM »

MC,thanks for the comments,I thought they looked a little excessive for mileage also,but they do wear.Were your carbs webers 40mm sidedrafts? I used a set of those(still got em)on 836cc and 736 cc bike,had to install 30 mm chokes if I remember right on the 736cc bike and Mallory dual pt distributor and h/p coil.I swear the bike went 10-12 mph more on top end.Thanks,Bill Benton

MCRider · « **Reply #31 on:** July 14, 2009, 02:22:30 PM »

Quote from: bellcow54 on July 14, 2009, 01:23:37 PM

MC,thanks for the comments,I thought they looked a little excessive for mileage also,but they do wear.Were your carbs webers 40mm sidedrafts? I used a set of those(still got em)on 836cc and 736 cc bike,had to install 30 mm chokes if I remember right on the 736cc bike and Mallory dual pt distributor and h/p coil.I swear the bike went 10-12 mph more on top end.Thanks,Bill Benton

Yes they were the DCOE40s and I think I used 32mm venturis. With the head and pipe it breathed very well and i dialed it in fairly easily. I had a Prestolite ignition and Andrews coils.

The pistons were .5 over so it was a true 750cc, the limit for my class. I may not have made 90hp, but that bike rocked. I agree those carbs work very well. On an 836cc they must be good.

My biggest complaint was they flared out and hit my knees pretty hard if I remember. I switched to 29mm Mikunis.

"754" here is using a set now as well.

Bill/BentON Racing · « **Reply #32 on:** July 14, 2009, 06:20:12 PM »

MC,Cool,I forgot to ask,did you use the straight manifold like Russ Collins sold(RC Engineering) or did you ever get to try Jerry Magnuson(made superchargers and did cyl head work) manifolds that were the proper shape-matched the intakes,they were damn sure easier to put on.Thanks,Bill Benton,gotta go Sat not far off.Will I make it?Stay tuned,time to prep cylinders and clean and measure.

MCRider · « **Reply #33 on:** July 15, 2009, 08:43:17 PM »

Quote from: bellcow54 on July 14, 2009, 06:20:12 PM

MC,Cool,I forgot to ask,did you use the straight manifold like Russ Collins sold(RC Engineering) or did you ever get to try Jerry Magnuson(made superchargers and did cyl head work) manifolds that were the proper shape-matched the intakes,they were damn sure easier to put on.Thanks,Bill Benton,gotta go Sat not far off.Will I make it?Stay tuned,time to prep cylinders and clean and measure.

Wow that's making me think back to a distant time...

If memory serves my manifold came in 2 pieces, bolted together between 2 and 3. The throttles were placed in the center so one short cable could be used. I think that's what led to them being splayed into my knees. Don't remember the maker.

If memory serves Weber design allowed for the throttle hookup to be on either side. If one would put the throttles each on the outsides, run a "y" in the cable, the carbs may sit closer in the frame. But you'd have more of a synchronization issue.

I'll bite, what are you getting ready for?

Drew75 · « **Reply #34 on:** July 16, 2009, 08:39:48 AM »

Additional rebuild pictures -

The Shop & Bikes - anybody notice that bodywork on the pool table?

Bill said if he can find the other 3 here we come 8360cc, new SOHC LSR!!

Bill/BentON Racing · « **Reply #35 on:** July 16, 2009, 04:30:37 PM »

MC,I think I am going to build CB836cc Tracy body bike,using some of the mods you mentioned and used,still got to read those other pages.The motor mount and and hand fit sounded good.I too think I will have better handling bike than before.What ignition system are you using? I used the Dyna,Gerex,Presolite,etc.,but seems to be a lot more to choose from now.I believe I am going with the paint on Drew's bike w/original 78F body on the table.His bike has tapered bearings up front and needle bearing kit in swingarm. Up in the air what shocks and other,so many possibilties!My first CB750 1975 I installed supercharger,8-10lbs.boost,one year later and lots of fun,each cylinder was down 30 psi.!!It's always a trade off,but one I can live with.Bill Benton

Drew75 · « **Reply #36 on:** July 17, 2009, 06:14:35 AM »

Cleaned:

Bill Race Bike:

Bill/BentON Racing · « **Reply #37 on:** July 17, 2009, 09:27:31 AM »

Pics of intake were as they came off bike after 31,000m,yes I ran something in the fuel system last time I serviced it,product works well,it's what I do,the pics of cyl head were as it came off also,Bwaller heres your pic of RSC/YOSH intakes on the 590 Yosh kitted bike.I believe 31mm's would fit fine.Pops head,TT cam,it weighed 372lbs. with fluids.Too much to list now,will post more later,there was a 5 and 6 speed CR trans for 500's,fit 550's?Turboguzzi what are you running?I would sell YOUR bike for that race kit Mark sold!Wow I wish I had that stuff,I might get back out there.Bill Benton,just kidding about your bike but I want to know more about it.

turboguzzi · « **Reply #38 on:** July 17, 2009, 11:18:24 PM »

Hei Bill

OK, found the manifold's post at the end!

they dont get me really excited to be honest, the "S" kink is almost as bad as in the stock ones...

TG

Bill/BentON Racing · « **Reply #39 on:** July 18, 2009, 05:30:39 AM »

TG,I agree,but was vast improvement over stock,I noticed manifolds in Mark's kit(Pops) looked much better,What ignition are you running?Are you and Bwaller Racing same organization?Bill

Drew75 · « **Reply #40 on:** July 18, 2009, 07:29:01 AM »

More pics of the build -

Bill/BentON Racing · « **Reply #41 on:** July 18, 2009, 11:37:02 AM »

turboguzzi · « **Reply #42 on:** July 19, 2009, 11:47:43 AM »

Quote from: bellcow54 on July 18, 2009, 05:30:39 AM

TG,I agree,but was vast improvement over stock,I noticed manifolds in Mark's kit(Pops) looked much better,What ignition are you running?Are you and Bwaller Racing same organization?Bill

Hi bill

I am running a mid 90's GSXR750 ignition. It is dead reliable, never had an issue with it. some parts were easy to fit some not really bolt on mechanically speaking, needed some custom fabrication

Bwaller is in Canda and I dont realy know what series is he going to race in

I am in italy and race in the Italian Federation (like AMA) clsassic championship.....

Bill/BentON Racing · « **Reply #43 on:** July 19, 2009, 04:00:38 PM »

Bill/BentON Racing · « **Reply #44 on:** July 19, 2009, 07:23:20 PM »

The ears and fork and drum out of no 2nd gear bike,I think he hammered 2nd and bent the fork,other wear occured after bent fork wouldn't allow full engagement of the dog and mating gear.Drum not real pretty either.Bill

nobody · « **Reply #45 on:** October 09, 2009, 02:03:03 PM »

I've got a 74 k4 with a faulty transmission as well. I missed a gear and broke something, nuetral light no longer works and it shifts so hard it hurts the top of the foot to kick up gears. I've got it somewhat stripped and should have the block on my workbench before long (still have to build a work bench, just moved). I was planning to rebuild the transmission myself, picked up a spare engine and a spare bottom end. I'm sort of a noob myself though so I've grown weary as I considered it more. Now I'm considering rebuilding the top end of the second motor, along with reringing and such (I think the compression is around 100/cylinder). My question is this:

With the spare engine on the ground, obviously not running, how can I tell if the transission is good?

I'd hate to rebuild the top end, throw it into the bike and find out I have two broken transmissions...

Bill/BentON Racing · « **Reply #46 on:** October 09, 2009, 08:28:33 PM »

You can't!,you can shift it and see if it catches all 5 gears,you can pull oil pan and inspect,but without running and rideable under load you won't know,It's a roll of the dice!

,Bill

nobody · « **Reply #47 on:** October 10, 2009, 07:16:59 PM »

Crap... I feared that might be the answer. How much of the engine needs to be stripped to split the cases? It might just be worth doing a top to bottom rebuild if it requires a lot of stripping...

MCRider · « **Reply #48 on:** October 11, 2009, 06:07:42 AM »

Quote from: mgab on October 10, 2009, 07:16:59 PM

Crap... I feared that might be the answer. How much of the engine needs to be stripped to split the cases? It might just be worth doing a top to bottom rebuild if it requires a lot of stripping...

As reported elsewhere, I have outlined the procedure for a trans operation without touching the top end.

Pull engine;
Flip over on bench;
Pull all sidecovers;
Remove lower case;
Fix trans.
Install lower case;
Replace all sidecovers;
Reinstall engine.

I've skipped a lot of details outlined elsewhere. But if you need them I'll rewrite them here. The topend does not have to be touched to fix the tranny (usually second gear and its shift fork.)

Bill/BentON Racing · « **Reply #49 on:** October 11, 2009, 07:24:11 AM »

MCRider right again,your top end OK flip that puppy over,take out upper bolts first,and get to work,check that s/drum also.Read a post for theres lots you don't have to remove; rotor,clutch,etc.theres a bolt under elec starter cvr,get it before u turn over.Good Luck,Bill

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Author Topic: Edit: Decided to Rebuild The Top End of other K4 (instead of repair trans) (Read 7191 times)

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