Author Topic: Bessie, my first rebuild: 78 CB750F3 (Back on the road 2016-05-12) (Read 70781 times)

brandEn · « **Reply #200 on:** October 21, 2013, 10:00:49 PM »

Hey glad to see this thread revived. Welcome back. I will be tagging along to see what comes of the fifth gear issue.

wohali · « **Reply #201 on:** April 21, 2014, 06:48:15 PM »

So Bessie's not been ridden since the rally in 2011. She racked up 701 miles exactly on that ride and has sat since then.

I spent the day getting the engine out and taking the head off. Here's what I found. Full gallery @ http://gallery.atypical.net/lr/cb750/2014-1/

I can't believe she looks this bad after only 700mi. The black sludge is still mobile, it's not completely dried out.

Advice welcome...really, really hoping I don't have to re-ring her again but I don't have any other good ideas. As previously posted, compression test didn't show problems, but perhaps my test was inconclusive. I'd rather it be the valves than the rings!

KayOne · « **Reply #202 on:** April 21, 2014, 08:28:19 PM »

Looks like #1 was not firing.

wohali · « **Reply #203 on:** April 21, 2014, 09:05:32 PM »

For only 700 miles? I would have thought #2-4 were not combusting properly (fouled with oil) and #1 is OK. I don't recall #1 being cold...but maybe.

rlvitt · « **Reply #204 on:** April 22, 2014, 01:33:46 PM »

wohali, Just started reading your rebuild a few days ago. Interesting build. I just finished a simi-rebuild on my K0. I didn't have to get below the cylinders. I've got my K2 completely torn down to the bearings now. The oil consumption problem you have? My hunch..... Check the valve guides and seals first. Then be really careful checking your rings and cylinder walls. If your burning oil, especially that much, you have gaps somewhere there letting oil by. Those seem the two most likely places to look. While the oil pump may be letting oil down into the sump, that isn't going to cause the long term burning you're getting. Your description of a "light honing" of the cylinder walls raises my antenna. Punch those cylinders out a size and put new rings in again. It's not that expensive and will cover that possibility for certain...... You're a detail kinda guy. Cover that detail.

Hondaman's ignition is pretty bullet proof. But, on the #1 cylinder I'd pull the plug and be sure you're getting a zap to it. It looks way to virgin to have been used.....

Good luck and keep at it. The ride will be beautiful once you get it right.

grcamna2 · « **Reply #205 on:** April 22, 2014, 05:16:31 PM »

Quote from: rlvitt on April 22, 2014, 01:33:46 PM

wohali, Just started reading your rebuild a few days ago. Interesting build. I just finished a simi-rebuild on my K0. I didn't have to get below the cylinders. I've got my K2 completely torn down to the bearings now. The oil consumption problem you have? My hunch..... Check the valve guides and seals first. Then be really careful checking your rings and cylinder walls. If your burning oil, especially that much, you have gaps somewhere there letting oil by. Those seem the two most likely places to look. While the oil pump may be letting oil down into the sump, that isn't going to cause the long term burning you're getting. Your description of a "light honing" of the cylinder walls raises my antenna. Punch those cylinders out a size and put new rings in again. It's not that expensive and will cover that possibility for certain...... You're a detail kinda guy. Cover that detail.

Hondaman's ignition is pretty bullet proof. But, on the #1 cylinder I'd pull the plug and be sure you're getting a zap to it. It looks way to virgin to have been used.....

Good luck and keep at it. The ride will be beautiful once you get it right.

+1

wohali · « **Reply #206 on:** April 22, 2014, 06:56:09 PM »

So given that the new scraper rings I had made up (when F2/F3 rings were unavailable) do not have the notch in them, and I honed at home, I'm giving in and bringing the cylinders to Gord Bush for a checkout and rework if necessary. If he can't get them true enough for regular size rings I'll have him go up to 1st oversize (0.25). Once I know the result of that I'll order in rings.

As for cylinder 1, well, I went to move the frame a couple of inches in the shop today and the "head" on the #1 wire came clean off! I'm going to guess it wasn't getting a good connection. That'd sure explain the lack of power at highway speeds...even with the oil burning

Today was getting my other bike ('03 SV650S) road worthy again, now that that's out of the way I expect to pop the crankcase tomorrow and see what's up with that pesky 5th gear.

wohali · « **Reply #207 on:** April 23, 2014, 04:53:23 PM »

First good news. Can you find what's wrong in this picture?

Of course in the process I snapped the tabs off the special spark plug advancer washer

Guess I'll be experimenting with the welder soon.

Tomorrow I'll re-measure gaps on the pistons and rings. Gord wants $350 to hone/bore the cylinders

If I have to spend that I might as well go 836.

grcamna2 · « **Reply #208 on:** April 23, 2014, 07:44:43 PM »

Look for a better deal on the piston boring/fitting even if you have to send it away to a forum member here,that's a lot. Go with a fresh set of pistons at least .50mm over.
You could install 2 pairs of CB350 twin pistons w/ the 3 piece oil rings... they're 64mm stock and Bore-Tech.com has some 65mm kits for a great deal.

Tintop · « **Reply #209 on:** April 24, 2014, 04:31:27 AM »

+1 does seem high. I just had the sidecar twin given a light hone, $20 a hole cash.

wohali · « **Reply #210 on:** April 24, 2014, 12:57:05 PM »

So for those who couldn't figure it out: 5th gear was on backwards. 10 minutes with the gear puller / bearing driver and she's working. I still have to put the crankcases back together, though.

Next step is I'm going to disassemble the intake valves and see if the seals look like they're on right. My theory is that the exhaust side would be slightly less likely to have oil dripping down them due to the pressure on that side, and also that I don't have the valve tool that makes getting the F2/F3 keepers in easier.

Anyone know any good tricks I can do with the head off to check if the seals are sealing correctly?

@grcamna Why new pistons? This engine doesn't even have 25000 miles on it. Can I not just get the 1st oversize rings and use the stock pistons? F2/F3 pistons sure are a pain to find as well.

If I have to go up to the 836 kit for F2/F3 it's easily going to run me > $1k and I'd rather not go that far if I don't have to.

grcamna2 · « **Reply #211 on:** April 24, 2014, 03:40:02 PM »

wohali,
I was thinking that it would be a good step to replace your pistons w/ at least a .5mm overbore so you can be sure that your cylinder walls are 100% round in all dimensions... I would recommend it if I were to have your engine come in for repair.
I think you can sell your stock pistons to help pay for the new ones if they're in good condition. imo
just trying to help

wohali · « **Reply #212 on:** April 24, 2014, 03:58:40 PM »

Thanks @grcamna2, makes sense.

I just measured the pistons and I do think my honing was a bit aggressive. More detail in my other thread here, I'll update this thread once I work out the details.

grcamna2 · « **Reply #213 on:** April 24, 2014, 04:12:53 PM »

wohali · « **Reply #214 on:** May 19, 2014, 02:09:27 PM »

Update: New Old Stock 1st OS (0.25mm) pistons received from eBay in good condition. They and the cylinders go to Gord Bush Performance in the Toronto area for boring tomorrow.

I also got a nice set of the inoxbolt.co.uk fasteners for the side cover since the oxide black ones I got from Canadian Tire decided to rust on the outside. (The insides look just fine, by the way. And I stand by my choice of copper anti-seize as a good galvanic intermediary.)

Tintop · « **Reply #215 on:** May 19, 2014, 02:58:57 PM »

When I rebuilt my 550 I replaced everything with SS to end the rust issue. Copper anti-seize was the recommended compound from the bolt supplier.

wohali · « **Reply #216 on:** June 06, 2014, 06:27:29 PM »

Cylinders are back, perfectly honed. 1 of the 4 pistons was "2-3 thou larger than the others" so they came back numbered on the cylinder block and the pistons.

With any luck I'll have the engine back together this weekend.

grcamna2 · « **Reply #217 on:** June 06, 2014, 07:21:30 PM »

That sounds good Girl

brandEn · « **Reply #218 on:** June 06, 2014, 10:08:44 PM »

Killer news!

wohali · « **Reply #219 on:** July 01, 2014, 03:27:09 PM »

Work stress + home reno == no time to finish reassembly. I was hoping Canada Day would be the trick but I am now preparing for a short trip to London UK (where I am seeing the Monty Python reunion!)

When I get back the reno should be done, the shop will be free of wood dust from the router and I should be able to reassemble the engine without worry of contamination.

wohali · « **Reply #220 on:** September 21, 2014, 07:47:57 PM »

Update: Bottom end is back together. 5th is working perfectly.

I also had to use the arc welder to build up the "tabs" on the spark advancer so that the washer would fit on correctly again. That was a 90A DC, reverse polarity, 7014 stick @ 1/8" thickness, then filed down. Took all of 30 minutes.

Next up: cylinders and the rest of the top end.

Jerilee · « **Reply #221 on:** September 23, 2014, 12:32:23 PM »

Great work! What was the culprit for the funky 5th?
Hope London was a blast, keep us up to date on the progress!

wohali · « **Reply #222 on:** February 05, 2015, 02:40:02 PM »

The "Can you find what's wrong with this picture" post should have been obvious to anyone who has gone into their bottom end:

Those scallops on the fifth gear are what latch into the "dogs" on the next gear away from the camera, causing the transmission to engage at fifth gear. Yup, that gear is on backwards.

About 10 minutes with the bearing puller and my moly grease and everything is back together.

I've been struggling with bad illness the past few months and haven't been able to get the top end back together, or the rest of the bike. I'm hoping to do that in the next month or two, so I can make the rally in Ohio in August. I will definitely bump this thread with new pics as they are taken. I finally upgraded my camera, to a Fuji X100S, so I'm always on the lookout for things to take pictures of

grcamna2 · « **Reply #223 on:** February 05, 2015, 04:34:14 PM »

Good to hear your making progress,hope you feel better soon.

wohali · « **Reply #224 on:** April 24, 2015, 04:37:25 PM »

Slowly, slowly getting back into the shop after extended illness since November

In the past few weeks I have:

ordered and received the CycleX MLS gasket set
cleaned up all of the mating surfaces, which were already true, and checked them with my Starrett straight edge
shrink tubing on the "outside" studs so they don't rust
re-installed pistons and rings and started put the cylinders on

And then...disaster. I was tapping the top of the cylinders with a wooden block to get cyls 2 and 3 + their rings in (using homemade piston rings made from pipe clamps) when the entire thing finally gave, and the cylinders dented pistons 1 and 4 on the edges!

I'm taking the night off because I'm really, really upset with myself and I've learned from experience I shouldn't work in the shop when I'm upset. Tomorrow I'm going to go back and see if the dents have pushed any material out of round and if so, file them down. I don't think the small gouge in the top is an issue, but if any is sticking out and gouges the cylinder wall we'll have problems.

These pistons (F2 0.25OS + rings) were damn hard to find and I don't have any other option at this point other than moving to 836, sending the cylinders for yet another overbore and so on. Shop will charge me $80CAD a cyl up here, and yes I've asked around and can't find cheaper. Plus there's the $500 or whatever for new pistons...super bummed.

If I can't salvage the pistons as they are, I'm just going to say #$%* it and give the entire engine to a shop to re-assemble, the bike being in the shop for 5 years now with only the 700 miles on it from the Toronto-Niagara Falls-Detroit-Toronto run is hurting me emotionally too much.

Really, really hoping this is salvageable...

News:

Author Topic: Bessie, my first rebuild: 78 CB750F3 (Back on the road 2016-05-12) (Read 70781 times)