Topic: cylinder wear help? 78 CB750 SS F -- HOW FAR TO HONE?

[70CB750]

I drove APE guides in the head with just an aluminum washer and grade 8 1/4" bolt.

No heating, no freezing and no banging

[filipo]

Awesome.

Tell me, is it necessary/advised to install new valves with the new guides?

[70CB750]

My exhaust valves were shot - with dimples where where the arm hits them (78F engine) - they were ok as far as play.  I had to replace both, I guess if the valves are good - as measured in tolerances - you can reuse them in new guides.

But new guides mean recut valve seats and lap valves in the seat.

78F is a can of warms, I think you know it too

[filipo]

78F is a can of warms, I think you know it too

I'm learning...

[bryanj]

Had to say it as it would have been a real bummer to sort the pistons etc then find it burning oil 'cos of the guides

[AJK]

How big of a feeler gauge will fit? (I think you were pretty close on the hone job after 1 minute; 6-8 might have been pushing it a bit. )

+1

I'd be happy to take the glaze off, 15 to 20 secs worth. Less material off bore == tighter tolerance (assuming the bore is reasonably in spec in both tapper and roundness & can be reused).

Ridge reaming.. Is it for the birds?
http://www.captain.norton.clara.net/cnn3sec14.html

[filipo]

This is interesting. I measured the remaining cylinders, via turning each upside down and sliding it down its cylinder, measuring at 90 degrees to the pin. Here's what I found:

#1 (honed): largest feeler is .004", and really really only just barely
#2 (not honed): largest is .0025"
#3 (not honed): can't get the piston in
#4 (not honed): can't get the piston in

On #'s 3 & 4 I can get the pistons in the "regular" way, i.e. tops of the pistons going in the bottoms of the cylinders -- but I can't fit #$%* in there other than the pistons -- i.e. no feelers.

Wish I had measured #1 before I honed it (I know, I know), but -- any ideas why 3 & 4 would be so much tighter than #2?
Wouldn't it either be 1 & 4 or 2 & 3 with approximately the same wear? Or does firing order have nothing to do with that?

Kicking myself again for over-honing #1. Ah well...

[AJK]

Yeah it happens to all of us. Don't feel bad. 4 thou on #1 seems excessive as the books minimum is 10 times less than that. 25 thou on #2 might be workable but i think thats getting out of spec as well.

I try and measure at different points in the bore to get a handle on how tappered and out of round each bore is. In both 0 and 90 degree directions at the top, middle and bottom of each bore. Then make notes of your clearances measured as this can tell you a lot. Draw a picture of it so you can get a handle on how each bore looks after taking some measurements.

  I had 2 different cylinder blocks to play with, one came out of a bike with low miles & was really good & ended up using this in the end. My original one was way out of round and tapered & was blowing smoke continously, the rings had had it. On the good cylinder, i just gave it a light hone. All your really wanting to do is take the *minimum* amount of material off to remove the existing glaze and apply a cross hatch to retain oil and also to allow the new rings to bed into and seal properly. The use of the hone allows you to keep the grinding action true in the bore, but you only need to use it in a minimal way. Everyones got their own take a style with these things.
 I know some old folk that used to race. They would deglaze/hone the bore by hand using emery cloth, they would not even use a hone just so they could be real gentle with the bore. I'm not saying to go to this extreme either, but there was some wisdom behind this. Remembering that the only difference between a good engine and a bad one is 'tolerance'. Once a motor gets excessively sloppy (out of tolerance), its called 'worn' and behaves as such.
  I'm not that picky with the ridge unless its excessive. There are different schools of thought on it. Of course getting rid of it all together is the best, but i think its more important to look at the state of the bore in general & skirt clearances before getting hung up on the ridge. A lot of mine honed out so i didn't really have a problem with it, but i've done other motors (mainly with cars) with ridges that were a bit pronounced and still didn't end up having problems with broken rings, etc, after many years of driving after that.

Worst comes to worst, you could:
  (a) try what you have
  (b) source another bore (std size if thats what yours is) and measure against that. There might be some good ones still findable.
  (c) get a piston kit and rebore, next size up or a 836 kit (better)


I personally think you have overcooked #1 so would avoid (a) if possible. If you reassembled it as is, you could probably ride it, but it would be iffy how much life you got out of the motor due to future issues with #1. You could do it if you got desperate.
  Option (b) is a better way to go. You might be able to source a decent cylinder block on the cheap thats not that worn.
  Best option is to go for (c) if possible and you get some more ponies out of the motor as well & benefits of increased compression as a side dish (and get to reuse your existing cylinder).

I've just put on 2000kms on mine since doing a light hone & reusing my std pistons. The bottom end was fine, so i didn't need to touch it. The bike runs like new, there is no smoke coming out the back and its using no oil. Most running in happened in the first few hundred kms. After rebuilding, i did 1 start-up sanity check, then on the next startup, I was ready to take it for a ride to give the new rings some load. Gave it medium revs, but climbing hills and backing off to allow for cooling. After 20kms, dumped the oil and filter (heaps of metal shavings came out here - most of the wear occurs here because everything is fresh), then installed new oil and filter. Did the same after 500 kms (less but still a significant amount came out here). Just checking my oil now after 2000kms and there is only very little 'glitter' to it, less than before, so most of the wear-in has occured. My piston-to-skirt clearances were around the 1 to 1.5 thou mark and I remember having a ring end gap of 11 thou from memory, so it was all pretty good. I just relapped the valves and installed new valve stem seals. Everything up top wasn't too bad. I'll keep oil changed regularly on it and expect to get a decent life out of the engine. It redlines nicely.

Good luck and i'm sure it will come good for you.

[Red Good]

If it is really that far gone , ship me your cylinder and I will put a good used /in spec sleeve in it surface the head and measure it all and hone it . Or do the big bore for you . I have the economy kits in stock , but would have to order a Wiseco kit  as we are out at the moment . What ever you want to do . Red 1-918-479-4200

[filipo]

Worst comes to worst, you could:
  (a) try what you have
  (b) source another bore (std size if thats what yours is) and measure against that. There might be some good ones still findable.
  (c) get a piston kit and rebore, next size up or a 836 kit (better)

I personally think you have overcooked #1 so would avoid (a) if possible. If you reassembled it as is, you could probably ride it, but it would be iffy how much life you got out of the motor due to future issues with #1. You could do it if you got desperate.
  Option (b) is a better way to go. You might be able to source a decent cylinder block on the cheap thats not that worn.
  Best option is to go for (c) if possible and you get some more ponies out of the motor as well & benefits of increased compression as a side dish (and get to reuse your existing cylinder).

Thanks for the note, AJK. I think (b) is the most likely option, though it might be difficult to find a good used block. The ones on ebay all have cracked fins, and it's hard to get an idea of their condition from a lot of the sellers.

Although, that said, Red might have the solution with replacing just the sleeve. I'll get in touch, Red!

If it is really that far gone , ship me your cylinder and I will put a good used /in spec sleeve in it surface the head and measure it all and hone it . Or do the big bore for you . I have the economy kits in stock , but would have to order a Wiseco kit  as we are out at the moment . What ever you want to do . Red 1-918-479-4200

[AJK]

The single re-sleeve option offered by Red is another option for you as well. I didn't think of that but thats also possible.

I forgot to mention to measure your piston skirt diameter and check that they are in spec according to the honda manual. This is so you can be sure that your piston skirts are not overly worn/scuffing and can be re-used. If they are worn, then that might rule out option (b), but i think you will be fine in this respect. Everything is about measurement & tolerance.

Option (b) worked for me and I was just lucky, but look at the other options as well. Given that there is a bit of work (and rework) in what your doing, i'd be tempted to avoid option (a) and being a bit more patient until you can get a more long term solution. Do it right the first time.

[filipo]

Well #$%*, man -- it's taken me since summer 2012 to get to this point, so "patience" and "taking my time" are clearly concepts I can handle.

Will definitely check the piston spec. Thanks again.

[AJK]

Summer 2012? Mine took 5 years to get on the road, 2008 till this year. I feel your pain.

a little hint.... if you don't do it right now, you'll be doing it again 

[goldarrow]

Flex hone is great for honing, and with time and persistence, you could get your bores next size up in no time

[Red Good]

Goldarrow , have you ever done that ? Resized a four cylinder with just a flex hone ?

[KJ790]

Just a note on running flat top 836cc pistons with an F2 head. I have had many people on this forum try to tell me it doesn't work despite the fact that I have been riding one like this for years without an issue. I built the engine a couple years ago using the cheap ebay flat top 836cc pistons with an F2 head. I wound up shaving .060" off of the head to get the compression ratio up to around 10.5:1 and still had good clearance between the valves and the piston. I did have to degree my cam afterwards because dropping the head this much throws your cam timing off a couple degrees. If you are looking to go stock compression ratio with these pistons then around .040" off the head should be about right as Hondaman has said.

[70CB750]

Goldarrow , have you ever done that ? Resized a four cylinder with just a flex hone ?

I am afraid it will get the cylinder out of roundness, not recommended.

[goldarrow]

Goldarrow , have you ever done that ? Resized a four cylinder with just a flex hone ?

Personally never done it.  But have read story somewhere in the forum while back.  If rpm speed of flex hone is consistent along with going movement, I don't see why bores would be out of round, but then again, I don't have first hand experience on this and no skills and tool to do it or even try.   

But my thought is that if you're going to up the bores size anyway, and have plenty of time and patience, why not give it a try.  What's the worst thing could happen? Bring the cylinders to machine shop to have it bore out, right?

[HondaMan]

Goldarrow , have you ever done that ? Resized a four cylinder with just a flex hone ?

I am afraid it will get the cylinder out of roundness, not recommended.

It doesn't work: tried it.
There was once an engine shop here in town, near where I worked (for 11 months) who bought a 4-hone flex-hone driver machine from a defunct Detroit shop, then fitted it with a series of ball hones and proceeded to "bore engines" for people (car engines, that is). Within 6 months, they had so many cars and engines coming back for warranty work (serious oil burning problems) that they just closed up and disappeared.

Ball hones are fine for applying the finish hone you need to break in new rings, but they are not made for boring straight lines. Use a 3-stone, with longest-possible stones, hone when doing these engines. The one I have are almost as long as the cylinders, and I wish I could get ones that were longer. The real big ones used for bigger car engines often won't compress far enough to fit into our 2" bores. though.

When you use long, straight stones, you can easily see the ridges at the tops of the bores as you hone. This helps you to see when you are done honing.

[74750k4]

Well that makes sense...  the long flat stone hones tend to take off the high spots, whereas the dingle ball hones conform more to the existing shape of the cylinder. Maybe best to first run the flat stones, check, then run the ball hone.

[Red Good]

If it's just a freshen up then I hone it 4 inch flat stone on a Sunnen hone . If it's going more than that I put them in the boring bar and cut them undersize and then finish them with the Sunnen . Red