Topic: Need 1000cc piston advice - vintage Venolias vs. new DPs

[Bill/BentON Racing]

And yes better check tensioner still in the cylinder, lol, been there! , Bill

[PeWe]

If I knew what I know now, it shouldn't happen!

[calj737]

Will hopefully get the cylinder machine work, maybe some head work done by MRieck.

If you don't send your head and cylinders up to Mike, there's a very good and competent shop in Richmond thats near enough to you. Ballos Performance Machine. See Stuart when you drop in, he will do excellent work and they are very knowledgeable and experienced with these motors. Nobody better than Mike for head work though!

[Austrian_CB]

Oh nice ... I'll receive my pistons tmrw. Then i'll contact Mike sometime this weekend or next week to see if he's willing to do it for me!

Otherwise i'll definitely be checking out that shop calj737 ... thanks for the tipp! Richmond is close enough too. 

[Austrian_CB]

Also ... what piston ring compressors are you guys using? Kinda worried about the oil rails now. So far I have a ton of compressors for car engine pistons but only one from the auto parts store that will fit the CB pistons...

[PeWe]

Fingers, screwdrivers    I like nylon screwdriver that is both soft and hard enough. I have one used in electronic industry when adjusting live electronic components.

Now when you are aware of the risks and go slow, everything will be OK. Test mount with cylinder on bench and find out the method. I found that "vibrating" the cylinder down with screwdriver thru the actual pistons wristpin, alternate piston 2 and 3 to start with, cyl went down horizontally made everything much easier. When 2-3 are done, 1-4.

 I found that method after I had pinched a rail.

One more mistake to not do, drop a circlip inside case. Cover the holes carefully around each piston, all of them. I mount one circlip on each piston on bench first.  2-3 need to get the inner circlip when mounted, cam chain side. 1-4 the outer to be mounted when pistons are assembled on rods.

After that always cover the cam chain tunnel since small metal stuff wait for jumping down there. Tools are magnetic and small washers will attach and let go over the head, same with sticky oily fingers where small metal things will attache and fall like bombs over the head with open cam chain tunnel. They have not succeded yet but the nasty washers and other small things tries at each rebuild!

CB750 has 2 different stock cam chain sliders, early short and later longer. The older shorter has thinner pegs where seated in cylinder and will make noise. Longer is better, thicker pegs.

[Bill/BentON Racing]

The longer is better for sure. If you can find them, Honda's OEM piston ring compressors, the middle part number 283, was made for the first DOHC 450 work pretty good. A nice champher on the bottom helps also. Also something under the piston's on 2&3 so they don't rock. Time for 1&4 there won't be any room.

[PeWe]

Keep pistons still .. I used what I had... cork sanding blocks

[Medyo Bastos]

Wow, nice work guys! I’ve always used my finger tips, kinda like using your 6th sense...

Billy I have 2 of those big roach clips too!


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[PeWe]

Finger tips too! I cracked 2 nails when I assembled my K2 std build engine a few weeks ago.
Cruzinimage 61mm pistons rings felt really hard.

Piston compressors would be nice to have. But I have no build within sight that need a pair of them.

[Austrian_CB]

First thanks to all of you for letting me know what to look for, will save me some money for sure haha 

Thanks PeWe for all the good info!! And Bill i'll keep an eye out for those compressor!

I was actually trying to go the different route and install the pistons incl. rods in the cylinder then slide the whole thing on in one piece and then bolt the rods to the crank .... now that I still have the cases apart. Good idea or no? (have seen it on youtube in one of those videos from the hackaweek tv guy)

Also thanks for mentioning the cam chain slider. Anyone have the part number on hand or know where to get it by chance?

[Medyo Bastos]

Bill i'll keep an eye out for those compressor!

i have an extra unused set.  let me know if you need them~

[PeWe]

Cam chain slider is the later model. Std for K6 as an example. Longer introduced in K3 according to CMSNL
14611-300-000
https://www.cmsnl.com/honda-cb750k6-four-european-direct-sales_model14384/guide-cam-chain_14611300000/#.WiMORWjWzIU

Earlier shorter with thinner pegs: 14611-312-000
https://www.cmsnl.com/honda-cb750k1-four-1970-1971-usa_model14354/guide-camchain_14611312000/#.WiMOs2jWzIU

Here they mixed. I noticed that the last one I installed to 1984 was a short model.
A friend noticed me about the thinner pegs recently. I knew that earlier were shorter but not looser fit. I planned to reuse my old short one, still looking good in my K2 build with K1 cyl + head but changed my mind to a long one.

You'll see that the cam chain tensioner complete has some parts.

I assembled my pistons with only 4 cyl studs in which gave me free room to assemble the pistons and press the rings.

The 2 studs with o-rings are a must, the other can go in later when you know they all fits. I had removed them when tearing the engine apart in frame. It went together in frame too. Except for the crank cases with all parts in, worked on the floor to avoid heavy lift and lift it aout-in alone. A strap around it only. Frame kit mad that possible.

The tiger pattern on upper case base gasket area is caused by tape protected the freshly grinded surface when cleaning the cases in machine dish washer powder  mixed water. The paper tape lost the grip in the water and alu colored dull gray. It was shiny alu after 400 grit paper (before that 240 so the case can use RSC base gasket.
Cylinder base had really nice new surface thanks to the manufacturer of the block!
RCS base gasket works well, but need good surfaces.
Fiber gasket for 78mm holes might not keep together that well either

The holes for sleeves are roughly grinded off since one case stud did not came loose and I could not leave it to a machinist and make it perfectly as planned. I had to do it manually with a drilling machine, electrical screwdriver with grinding tool. RCS base gasket with dowels as template where to cut. It holds together!

[754]

When I put my motor together last August, the long tensioner, appeared to hang up on the tunnel on my 74 motor.
Because I did not want it jamming, I had the head off again, masked everything off, then  cut the tensioner with a file... notch it til, I could break it off, then dressed up the end with a file..
 Actually I had quite a few issues  puttingvtge top end on, went from low buck hotrod to lowbuck stocker.. but hey..got me to the Reunion..

[PeWe]

When you say that Frank, I remember I've heard that from my friend that talked about the sliders. We compared heads and cylinders, he has some CB750 parts. Many cylinders have holes or almost after cam chain, (maybe no washer on cam)
But, I noticed it can sit very tight in the upper groove in cylinder. It's here the shorter sit wobbly. I used a new long with my JMR billet block, nice tight fit.
The long used one I put in the K1 setup did not sit that tight, better alternative than the short and no problem with tunnel in head.

Did it hook into the head cam tunnel, front upper side?

[754]

Front upper tip was sort of sticking. Hitting the casting.

[Austrian_CB]

Good info on the cam sliders! I'll just get an updated one then install both and see what will work out better.

Here are 3 photos for comparison between the 71mm Venolia's, that were in my engine originally, and the new JE 71.25mm pistons. Hope it will help some guys who wanna purchase them in the future.

[754]

 I dont think I needed to take more than 3 or 4 mm off the tensioner tip  but I was pressed for time, so I think I measured from the pin up and made it the length of the short one. I was upset because I had torqued the head, and then had to take it off again.

 So the lesson here remains the same..as 754 says, check, check and recheck.. a step I missed.

[PeWe]

Ok, better than need to remove the cylinder too to replace it.
This is something to check before and adjust what needed if needed.