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top end rebuild! need some parts and knowledge ..

Curtis87

CB750 Enthusiast
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I have started to tear apart my 1974K . I was missing one of these hollow dowels! Someone was definitely into this engine before but the bike was running for quite some time like this. I thought maybe I dropped it down the cam chain hole but my dad assured me he did not see anything drop. I inspected carefully and did not see anything down there.. So what are these called and how much affect do they have, I assume oil comes through..

IMG_2224.jpg

Secondly, I have two of these dowels on this part of the head, is there any others? Anyone have a link or checklist to what all should be there, thanks guys!!

IMG_2225.jpg
 
The small dowls in the head align the cam towers properly. No oil goes through them they are there for alignment purposes. Did you look on the underside of the cam tower?...they stick in there sometimes.

As far as your second picture you will only have the two dowls on the top of the cylinder. There will be two in the crankcase as well.

The biggest thing on these motors is to never use silicone, it will migrate and plug the oil orifice in the head and ruin the cam towers and cam. I see in your first picture the orifices are gone in your head...did you remove them?
 
I checked the cam towers right away , it was definitely not anywhere. What are the orifices? The coin sized rubber caps? I did remove those yes
 
No the oil orifices go in the heads in the two holes with the small orings...just above the hole you have circled in your first picture. If this stuff was gone when you dissassemble the motor I would be very afraid of what else was done incorrectly in the motor. The oil orifices are very important, without them you will starve the bottom end for oil.
 
Yep as you can see here I cleaned everything up today :) You are right, I do not have the orifices!!! Now what to do..... IMG_2251.jpg

Questions 1- will my 1978 engine have the same orifices that I could put in this 74 motor?
Question 2 - How do I remove the broken post rod shown here?
IMG_2253.jpg
 
yes the78 will have the correct orifices.

Just put a vise grip on the studs and turn them out...they are just threaded into the head. i would replace all of them...the one next to the broken one looks like it is stretched.
 
I just might as well.. OK so new topic here, I have discovered my poorly built engine has an 836cc 65.00MM bore kit installed. Pistons are pooched. Can I get a 65.25mm bore kit or will another 65mm kit do?? The cylinder walls are not damaged, even the honda shop said they are good, but they said something about after cross hatching the cylinders again maybe there wouldn't be enough material for the 65mm pistons???
 
If the cylinders are still good and within spec you can just have them honed. You have to have fresh crosshatch for new rings or they will not seat properly. Honing is just a surface prep process...very little material is removed but if the bores are on the large side to begin with you will increase that slightly more. You can use the 850cc kit as they are used to clean up worn 836 bores. What happened to the pistons? The 836 is an extremely reliable kit.
 
You will have to do some checking because the older kits used a bit more clearance then the newer ones do. The bore may be a bit too big for the newer style pistons. If all else fails all you need is a different stock block because 836 just uses stock bored out sleeves...no special machining just a basic bore job.
 
great, I think the plan is to order another 65mm 836 kit off ebay. The quick reading the honda shop guy took from my bore was just under 65mm as he said so my buddy thinks it is worth the chance to order another 836 kit. I have my other 78 motor so I will just use that cylinder and get it bored for the 836 if all else fails!
 
ON SECOND THOUGHT, i saw the cycle x 850 kit, all I need is the shop to bore my existing cylinder the .5mm extra, dam I think thats a far better Idea for 250USD then 300 CDN for the 836 kit on ebay. The thing is, i am not going to change the cam. Is it not a good idea to run the factory cam with a big bore?
 
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The cycle x pistons are far better quality then the ebay 836 pistons...unless they are wiseco pistons.

You can use a stock cam with the 836/850 motors but you are leaking power on the table. 836/850 with a stock cam and you really dont make any more power then a stock motor. Keep in mind when or if you do change cams you need to also buy rewelded rocker arms, they were together like cams and flat tappet lifters do in automotive engines. If you put used rockers on a new or different used cam you will ruin your new camshaft.

with the engine apart you should look into putting new primary and new heavy duty cam chain in as they are a weak link in the 750 motor.
 
good advice, so the honda shop has my head and is cleaning and checking my valves with new seals I gave them, but what are these in my gasket kit, I am now assuming they go with the valves as there are 8 of them.. IMG_2294.jpg
 
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