Locating pins on the cylinder
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  1. #1
    Senior Member Erwin's Avatar
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    Locating pins on the cylinder

    I have seen that some people use fatter Yamaha XS 650 cylinder studs on tuned CB 350's. In fact, from what I've read, it is a pretty common modification for racers. I also found them in a drag race engine I bought some time ago so I was thinking of reusing them on the engine that I am currently building. The fatter studs mean that you cannot use the stock locating pins. The engine I pulled apart did not have any of the locating pins on the cylinder or head. So I guess it worked on that engine. It was a good and leak free engine but I have no idea how much it has run with those studs.

    I was wondering how much of a problem the omission of the locating pins would cause. I was thinking that the cylinder base with the o-ring in the top case would provide plenty of centering and that you really do not need the locating pins.
    1972 CB350K3 General Export | 1976 CB200T K0

  2. #2
    Senior Member ancientdad's Avatar
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    I can't speak to the loss of the dowel pins, or knock pins as Honda calls them, but I really can't see the need for fatter studs. These engines hold together quite well even when modified radically (see outobie's uber cafe and other race engines, don't think he changed them).
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



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  3. #3
    Senior Member Erwin's Avatar
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    Quote: "Head studs seem to be breaking in some powerful motors, so they should be replaced with a set of 10 mm from Yam XS 650"

    Honda CB350 Road Racer FAQ, Engine Modifications Page
    1972 CB350K3 General Export | 1976 CB200T K0

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  5. #4
    Sensei 66Sprint's Avatar
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    Maybe in a 12:1 compression ratio engine, but typically not needed for a streetable engine.......The "knock pins" are there for a reason.....
    Maybe not so much needed on a race engine that will be torn down and rebuilt again after a relatively few hours of usage........

    JMHO......But I can't see Honda allowing the extra machining and manufacturing processes costs if those parts weren't necessary ........
    Last edited by 66Sprint; 05-16-2019 at 02:57 AM.
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  6. #5
    Senior Member Erwin's Avatar
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    One could also bore out the holes and use dowel pins from an XS 650.
    1972 CB350K3 General Export | 1976 CB200T K0

  7. #6
    Senior Member ancientdad's Avatar
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    Quote Originally Posted by Erwin View Post
    Quote: "Head studs seem to be breaking in some powerful motors, so they should be replaced with a set of 10 mm from Yam XS 650"

    Honda CB350 Road Racer FAQ, Engine Modifications Page
    Are you planning to build an engine with all the high performance parts at the same level as in the quote? And ride it at that level continuously in a racing situation? Because if not, it's highly unlikely you'll ever experience any issues with the stock studs... I drag raced a 450 continuously for over 2 years during '73-'75, most of that time 2 nights a week, with 12.5:1 pistons, MegaCycle cams and a stock 4 speed bottom end with stock studs, regularly turning 10,500 rpm and never had to tear down the engine for anything except a fresh set of rings once during that time.
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



    running points... because I'm too old for mysteries that begin with pushing

  8. #7
    Senior Member Erwin's Avatar
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    Yes, my engine will be at that level. But in all honestly it will not be used as a racer but as a sunny afternoon weekend warrior so it might be overkill. But in my mind overkill is not always a problem. I figured that it could be a worthwhile improvement that I could do for next to no money. Just for peace of mind.

    I also have Cappellini oil pump. You could argue that that is also not needed on a street bike. The only real improvement there is that it will deliver oil to the head faster on cold startups, that it has more capacity and that it keeps working under any circumstance.

    BTW: I do not know if you can compare a 450 to a 350 when you look a the studs.
    1972 CB350K3 General Export | 1976 CB200T K0

  9. #8
    Senior Member ancientdad's Avatar
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    Honda built them proportionately strong, and the 350 engine has been used probably as much or more than the 450 engine in race applications. While I understand your interest in going for it to avoid the potential issue, a weekend hot rod that will be thrashed hard for short periods of time - remember, on the street you can only go so fast for so long, and you're sure not playing outrun the cops with anything less than a modern bike with 100+ horsepower and even they get caught often - won't be run hard as long as it would likely take to grenade anything if it is assembled properly. Since what you're considering causes a secondary modification to allow the use of it, you open the door for secondary complications (proper cylinder alignment, gasket sealing)... if it were mine, I'd trust the vast level of experience right here in this forum of racers who have done it for a very long time (again, outobie for 20 years on 350s) and used so many original Honda components due to the overkill durability built into them by the factory for longevity/reliability purposes... again, remember that even Mr. Honda didn't likely expect these engines to be still serviceable, much less being modified to some level of race performance, 30 to 40+ years after manufacture - and my current 450 is one of them, undoubtedly running the original crankshaft and rods with close to 15,000 miles on it from multiple owners who most likely did not do proper or regular maintenance over the years, and yet it can go to the drag strip and get thrashed all night long with 11.6:1 pistons and MegaCycle cams while turning 1000 rpm over the stock redline, and then go riding on Sunday for me, totally reliable... to me, that's proof enough. But, do what you will if it makes you feel more comfortable
    Tom

    Ride along at the drag strip - https://www.youtube.com/watch?v=20jFPazXlvU



    running points... because I'm too old for mysteries that begin with pushing

  10. #9
    Senior Member TOOLS1's Avatar
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    Between the cylinders and case, they are not really needed, but you do need them between the head and cylinders.
    TOOLS
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  11. #10
    Junior Member corndog's Avatar
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    Quote Originally Posted by TOOLS1 View Post
    Between the cylinders and case, they are not really needed, but you do need them between the head and cylinders.
    TOOLS
    Sorry to necro this thread. I am currently rebuilding the top end on my CL350 and on disassembly, I only noticed 1 knock pin installed between the jugs and the head, while where was 2 on each the camcase-to-head and cylinder-to-crankcase junctions. It looks like there should be 6 in total of the 11x18mm pins. The head gasket has been replaced before, so I am sure someone left it out. If I can't easily (read quickly) track down another, are you suggesting the best course of action will be to install one pin on the crankcase-to-cylinder, and keep 2 on both the upper interfaces? Thanks!

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