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Having trouble finding engine studs for DOHC - Usable stock cylinder? '79-750 F

Beachumb

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Hello all, new here. A little background. Been working/ripping my '79 750 F Super Sport for a couple years now. Its been very testing. I bought it stock with a bent and leaking valves. I started by rebuilding the top end and rebuilding the carb bank. I sent the head out where they resurface the head, block and installed new valves in the head. I cleaned the pistons, had the cylinders honed and then I installed everything. This is where the head ache started. It wouldn't start, no compression.

Turns out the shop that installed the valves, forgot about cutting them to length. So I ripped it all apart. Again. :banghead: Sent the Head back, they cut the valves, installed the head. Boom, fired right up. Rip her around for a few months. Then 4th of July 2016 about 3 a.m. someone comes in the driveway and cuts everything they can find in the dark. Markers/lights/leads/batt leads/carb boots/brake lines ...... I fix, everything. Bike is ripping again and my blood that had cooled from a boil, to a simmer; is now back to normal temps......end of the summer 2017 my cylinder block cracks, bike is bleeding bad. After inspection, I believe the cam chain, which I have been meaning to replace (and should have when I did the top end :doh: for some reason I only replace the intake cam chain, was buzzing the side of the block where its thin wall and cut through the side.....SO. I am starting over. Again. And I would like this to be the last time I remove engine from frame, and go deeper than the head cover.

So I'm looking for advice or a lead on a new cylinder block. Only option I see is rolling the dice on eBay. They seem inexpensive. But are they usable?



Also, while I'm in there, I think Ill do the engine studs with some heavy duties but I can't find those either. See them for the SOHC but not DOHC. Any advice much appreciated.
 
There is supposed to be a chain guide in the engine that prevents any contact to the block. Am assuming you mean the front of block as the tensioner on the back side stops the same. You have to split the cases to change the long exhaust chain and maybe why you didn't do it.

You NEVER cut the valves on EITHER end, only the seats. The valves themselves unless stainless are surface coated only and any cutting on them will remove that to lower engine life down to maybe 10K miles. The valves do not get cut to length, they get different shims on the tappets to adjust them.

F bikes use the spiral type cylinder studs, which are as strong as any aftermarket ones ever put out (most of which are no longer available). The K, C, L, and SC 750s use plain old cylinder studs which are very weak. 900F uses the good spiral too but that and the other 1000 and 1100 studs are longer and do not fit in the 750. So, you would be looking for '79-'83 750 F ONLY studs that are spiraled.

Your cylinder issue will be that if still using the standard non-oversize pistons you will have fits finding a good condition cylinder, most will need to be bored to at least the next oversize. Meaning new pistons and rings too. And finding somebody good enough to do the work competently, not a given in today's world............
 
Thanks for response. Sounds like I can keep the studs that are in there. Both can chains are there. Yes that is why I did not replace the chain, I learned after that you can pop a link, hook in a new chain to old and thread the new one in as you rotate the engine. I could hear the chain buzzing, at certain rpms in 1st and 2nd gear. Maybe the block just cracked... but wear it bulged, then cracked.....on the opposite side in the same spot it was bulging and starting to crack. Thought that either A-the bulge is part of the cast or B my cam chain buzz was the sound of the cam chain bounce off this area and cutting through the thin wall. I’ll include a picture.

As far as the valves go, not sure what happened there. They cut the seats, I asked the local shop what was going on when I found no compression. They had the idea that the shop hadn’t cut the valves (it’s been two years since maybe I’m remembering wrong) but I do remember when I bolted the head on, the camshafts wearing kinda of floating and as I bolted the u shaped arms that hold them in place (canshafts) they depressed the valves so that they could not seat. No compression. I was asked to send the head back with the original valves and new again so they could match lengths...
 
When the valve seats get cut the valves sink deeper into the head, that being in an up direction, then the stems become too long. The rework is to use thinner shims to make up for valves too long now. Standard procedure is to set the valves again after any valvework.

Did you ever adjust the chains? Not doing that and they then buzz from being loose. Need to do it every once in a while.

The chains are Morse type multiplate like car timing chains and not roller type which could typically pop a link and then change to repin it. Morse type are more difficult to repin and the link kit much harder to find, many have bad luck with that type. The roller ones you simply ding the end of the pin up and done, the Morse type really needs a presstool to properly shape the end of the pin so it stays put well. That type chain generally comes endless and you split case to change them.
 
I wonder if they cut the seats too deep. I remember trying to put thinner shins in and not being able to get ANY clearance.


As for cam chain, I was going to order a new cam chain from vintagecb750. They offer the extra link and a cam chain rivetor tool for sale as well. To avoid splitting the case.
I have tried adjusting the cam chain tensioner adjusting bolts, maybe I need to re-research that process to make sure I’m doing it right. Is this what you mean by adjusting the cam chain? Thanks again.
 
If you want reliability get the Vince & Hyde AHM design tensioners available via JesBUILT nor Portland Oregon. You can also install an oil feed off the filter casing to the B chain tensioner to improve lube flow to that chain and remove air from the filter housing.
 
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