Topic: My K8 re-conditioning

[70CB750]

Hello from VA 

Following.

Hello 70CB750, what part of Va ?

I'm in central NC, near Raleigh.

I am up north by Warrenton.

[denward17]

#4 exhaust valve and seat, how bad is it?

[Stev-o]

Let's put it this way: I would not say it's good!

It has been my experience that a rebuilt head is one of the most important things to do on an otherwise good motor to get it to run excellent.

Do you know of a shop that you can get it vapor blasted?

[denward17]

Let's put it this way: I would not say it's good!

It has been my experience that a rebuilt head is one of the most important things to do on an otherwise good motor to get it to run excellent.

Do you know of a shop that you can get it vapor blasted?

I do not know anyone in the area that works on these heads, thought I would call the local Honda dealer tomorrow to see if they have a favorite machine shop.

Does anyone on this forum work on them?

[grcamna2]

Let's put it this way: I would not say it's good!

It has been my experience that a rebuilt head is one of the most important things to do on an otherwise good motor to get it to run excellent.

Do you know of a shop that you can get it vapor blasted?

I do not know anyone in the area that works on these heads, thought I would call the local Honda dealer tomorrow to see if they have a favorite machine shop.

Does anyone on this forum work on them?

I think you should PM member 'dragracer' ;he helped me with a machine shop in NC. once who did great work for a good deal.

[newday777]

more pics:

Does the rubber rollers look ok to re-use?

It's a whole lottah work to get to fixing a screwed up motor(valves, pistons, rings, cam, rockers and possibly more). Replace them unless they are fresh in the past 5 years.

[70CB750]

#4 exhaust valve and seat, how bad is it?

I have a set of Neway seat cutters I used on Red  - she needed new guides and valves and retainers, being 78SS engine.  If you want to go that route you can borrow them.

But I would start with having the head blasted clean, than leak test and maybe all it needs is some lapping. 

[BenelliSEI]

That seat looks OK to me. How is the guide (check the way PeWe suggested). You are keeping track of which valves came from what cylinder? It’s important they go back where they came from.

Clean it all up to your satisfaction. Lap the valves in lightly, by hand. Reassemble the head and flip it over. With a spark plug tight in the hole, fill each combustion chamber with varsol or thinners. If any leaks out the ports, do that valve again. Lightly...

[grcamna2]

That seat looks OK to me. How is the guide (check the way PeWe suggested). You are keeping track of which valves came from what cylinder. It’s important they go back where they came from.

Clean it all up to your satisfaction. Lap the valves in lightly, by hand. Reassemble the head and flip it over. With a spark plug tight in the hole, fill each combustion chamber with varsol or thinners. If any leaks out the ports, do that valve again. Lightly...

I use a fine grit lapping compound(if I lap at all)to keep from cutting the valves & seats too much.
I much prefer having my excellent Powersports machinist use his machine which has fine stones and doesn't take much off;he has a better eye for checking the valve guides than I do. 

[denward17]

I will get all the valves out next week and measure valve/guide looseness.

I just checked the exhaust valve I took out, and if my eyes are not deceiving me, I have about .018 wiggle.

That looks like it is out of spec.

Is it normal to just replace all the guides, or just the ones out of spec?

[grcamna2]

Head and cylinders are off, now time to do some cleaning and pull the valves out.

How do these pictures look for wear?  I suppose I need to get new rings since I took the cylinders off.

What's a good source for rings/gaskets?


Thanks for any info.

I would have a qualified Powersports machinist measure the bores of the cylinders and the piston skirt's O.D. to be sure they're still 'in spec'. Do you have an inside mm micrometer? then you can measure the cylinder bores and a good calipers to measure the piston skirt's O.D.

A good gasket set is Vesrah and I think it would be good to replace your piston rings,if nothing else.
I just found that jetsrus.com also sells Shindy piston rings which are good quality Made in Japan for a good price.
I would check what size rings you need after measuring the cylinder bores then use the OEM Honda part numbers and see who has the rings available.

Those parts all need a strong decarbonizing to remove all that junk so you can work with them.

[denward17]

Continuing to look at valves and valve guides.  Looks like I need to replace all the exhaust valves/guides and possibly intakes.

See this thread:
http://forums.sohc4.net/index.php/topic,191558.0.html

Trying to find a local machine shop to perform the work.

[denward17]

Decision has been made to get head work, at this point all new valves and valve guides, so have to make a decision on who will do the work.  More $ than I realized.

Also got the pistons off today, cleaned up and measured end gap on existing rings:


Back view first pic, then front view



End gap of top and 2nd rings in all cylinders look good, so not sure I want to re-ring it.

#1 T .016, 2nd ring .014
#2 T .016, 2nd ring .013
#3 T .018, 2nd ring .013
#4 T .016, 2nd ring .014

I cannot feel any grooves or scuffing in the cylinders.

[grcamna2]

The ring end-gaps seem excessively wide;that's w/o me checking the book for the proper spec.
I love the Super Sport OEM pistons 

[denward17]

The ring end-gaps seem excessively wide;that's w/o me checking the book for the proper spec.
I love the Super Sport OEM pistons 

The only guidance I see in the workshop manual for end gap is  .0079 to .016, so that pretty much answers the question that I should change the rings.

I measured all pistons:
#1 -- 2.403
#2 -- 2.400
#3 -- 2.412
#4 -- 2.403

Book indicates if less than 2.3939 they should be replaced.

I assume pistons are ok.

[denward17]

Measured end gaps of rings again, this time near top, middle and bottom.

I only used the top ring in these measurements.


What do these results indicate?  Hopefully that the bores are ok?

#1
T--.015
M--.016
B--.016

#2
T--.016
M--.015
B--.015

#3
T--.018
M--.017
B--.017

#4
T--.016
M--.016
B--.017

[SOHC4 Cafe Racer Fan]

Really great head work from a craftsman such as Mike Reick is not cheap, but the work is superb.  No complaints.  It just works beautifully.

[denward17]

Head is off to MRieck.......

Trying to decide what over size pistons to get, probably the CI 0.5mm over.

While waiting trying to clean and paint.

Cleaning/sanding bottom end today/this week....

[grcamna2]

Head is off to MRieck.......

Trying to decide what over size pistons to get, probably the CI 0.5mm over.

While waiting trying to clean and paint.

Cleaning/sanding bottom end today/this week....

I wonder if painting the bottom is the best choice ? That engine looks very nice and clean as bare aluminum. I don't paint them because oil gets down there and keeps it from getting corroded anyway;some members like to see it painted.
I know it's up to your preference though;I always like the look of cast aluminum on the cases,imo. 

[denward17]

Well, it has paint on it now, looks like from factory, it is flaking off with some brake cleaner.

I did have the thought of just cleaning it up good and leaving it, but since I started sanding, I will probably shoot some primer/paint.

[BenelliSEI]

Nice prep work. Did you take the pan off to check the oil pump pick up screen is clear/clean? Often a waste of time, but you have time and are staring at it.....,

[denward17]

Nice prep work. Did you take the pan off to check the oil pump pick up screen is clear/clean? Often a waste of time, but you have time and are staring at it.....,

Dang it.....now something else to think about   

[PeWe]

Nice prep work. Did you take the pan off to check the oil pump pick up screen is clear/clean? Often a waste of time, but you have time and are staring at it.....,

Good idea!
Open pan and look inside important to do with some intervals.
I usually do it after ca 1000km on a fresh rebuild. Sealer and other stuff can land in the pump  strainer.

An unknown engine can have debris, oil sludge inside that can block pump so oil will not return to tank and feed engine in time.

Also a chance to measure the primary chains slack.
New chains 65mm, replacement when >70mm which take much longer time than 22k miles.

[denward17]

Popped off the oil pan to just have a look see.....looks good, no major bits or pieces.

Does the oil screen pop out for cleaning?

[PeWe]

Let it sit there. Too easy to deform when removing it.
No reason when clean inside.

I usually use a brush to carefully remove small dirt in the strainer (net).