cylinderhead overhaul

[andy_c101]

[continuing on from my December thread....... I know I'm a but slow at this game]
[http://www.sohc.co.uk/index.php/topic,4090.0.html]

I did decide to 'live with my slight oil weep' from the head gasket for a while, but now the old girl has taken up smokin'!

Compression test seemed good (?) at around 150-170psi; so I'm thinking it's probably valve stem seals.
& for all I know they may well be 35 years old!
So having followed the 'if it aint broke dont fix it school', it's now broke, so i need to fix it!
This means off with the head, to do valve seals and the gasket/oilways; & generally check it over.
- at least I'm a dab hand at removing carbs (down to 30 minutes after several years of training!); the pipes are off (me thinks I may need to do something with those down pipes too... probably throw money at them).
-rocker cover off, but one of the two camchain sprocket bolts is seized on solid, and the flats are now rounded. Doh!
 I think I'll have to invest in a set of "Irwins bolt removers".

http://www.screwfix.com/p/irwin-5-piece-bolt-grip-nut-remover-set/96028?cm_mmc=GoogleBase-_-Datafeed-_-Automotive-_-Irwin%205%20Piece%20Bolt%20Grip%20Nut%20Remover%20Set

- any tried those?

I let you all know how I get on....

[hairygit]

I recall helping a mate do a rebuild on a 550 many years ago, and the camchain was fitted with a spring link, which means you can split the chain and remove the head without romving the cam sprocket. As far as I know a split camchain was standard, as the motor had not been apart from new (all the yellow paint was still intact on the rocker bolts etc) but for a definite answer, Brian J is the man who'll know for sure!

[andy_c101]

I resorted to using an "Irwins bolt remover" socket on the camchain sprocket fixing bolt.
It has chewed the bolt head, so it will need replacing for the rebuild;
but the Irwin tool worked a treat.

The next snag I found is with nut/bolts numbers 2,3,&5 (the inner ones that have the rubber sealing cap) and are buried deep inside the narrow access hole in the head casting - (photo).

first my 12mm A/F standard 1/2" sq drive socket o/dia is too large to go down the access hole;
so using my (cheap) small 3/8 sq drive socket, the heads of these nuts rounded off!
- this despite soaking for half a day with 3-in-1 penetrating oil, (& then after the first difficult nut) using the hot air heat gun.

- ahah! I have my Irwins sockets!.....but...... they have a 3/8 sq drive and whacking-greater Hex-A/F; the hex prevents it going deep enough down the bolt hole.

- only one option..... file the flats off the Irwin socket, down to approx 18mm o/dia! (photo - & that was onlyhalf way).
-  eventually the Irwin socket did the trick, three times over it worked.

I shouldn't  be surprised, this is often the challenge (with 30yr+ old bikes) dealing with those siezed/sheared fasteners.

next task is to lift the head ..... and see what lurks inside.....
( I didn't have time tonight, and didnt want to rush that)

[Bryanj]

Use only 6 sided sockets when doing the head bolts, if you can find a supplier there is a whitworth socket that is a "Hammer on" fit on a 12 mm hexagon (3/16 or 1/4 but cant remember which!) as to the spring link on the cam chain that was NEVER a fitment from Honda on any of the fours but the 450/500 twin SOFT link is a fit if you want to change the camchain without splitting the crankcases, speaking of which if you do split the crankcases a new primary chain is a must even tho' its expensive.

[andy_c101]

The head is off.
My attention first was directed to 4th cylinder, exhaust valve/seal.
I could see into No4 Ex/port, and the port had a trail of oil from the lower valve stem.
Next I removed No4 Ex valve springs, then eased off the valve stem seal.
The stem seal lip has a 'nick' on the lip (at about 10 o'clock in the photo)
but then on wiping away the oil remnants, I see the top of the valve GUIDE is cracked! (3 o'clock & 6 o'clock, in the photo)
No wonder she was burning oil on No4.
- need to take a close look at all the valve guides now.......

Has any one else come across this type of valve guide failure before?

[Bryanj]

Cracked guide is usualy due to valve stem getting bent when re-assembling the rocker cover to head and not reading the book!!

[andy_c101]

Bryan,
yes I see what you mean (- & I have found the specific note in the manuals about tappet alignent on rebuild).

I'm finding a few little signs that 'someone has been here before'!
actually that particular valve does not want to fall cleanly through the guide (suggest one or both are not 'true'; it also looks 'newer' than others (ie less carbon buildup on it)
- one cylinder stud is definitely newer (shinier) than others;
- some of the rocker cover bolts are black-bolt capscrews (unusual for Honda?)
- and a couple of 'dinks' on the rocker gasket faces, indicates carelessness by someone in the past.

I guess that's often the case with an old bike with big gaps in its history.

[andy_c101]

continuing the tear-down....
it just got expensive!
I find 7 out of 8 valve guides have hairine cracks, and the valve stems have a tight spot too! (indicating a slight bend inthe stem; sure enough once removed the bent stems were confirmed.

BryanJ was right, someone (previous owner/monkey!) has fouled the rocker arm and valve stems on assembly; there's even a slight 'dink' one on the top edge of the valve stem.
- anyone ever heard of this so bad before?

So its new valves & guides required; but No4 Ex/valve (the worst offender) has obviously been putting high contact load on the rocker/cam lobe, that cam lobe is now right on bottom limit. 

I guess my best bet is David Silvers or CMSNL for parts?

Q1: Anyone know where I can obtain the 5.5mm guide driver tool?
Q2: When i get new valves & guides, I DONT have to ream the new guides do I?
Q3: Can I just lap the valve seats into the head or do they need 'properly re-cutting'? If so any suggestions for cutting tools?
Q4: if anyone has a half decent camshaft.... ??

On the plus side the cylinder bores look good & measure up A-OK, as do piston ring fit/clearances.

At least I found the problem...
i better start saving the pennies.

[UK Pete]

Hi Andy have a read of this  http://www.sohc.co.uk/index.php/topic,4330.msg19487.html#msg19487
pete

[Bryanj]

The drift is easy to make; yes you DO have to ream the new guides; yes you DO have to cut the seats. Put some pictures up of the cam and relevant follower to let us see how bad they are.

And your cheapest repair is a used complete head, dont forget all the 500 and 550 SOHC fours use the same head

[andy_c101]

Firstly to Pete:
Looks like you did a great job on yours 750(?) head.
Where did you buy the cutter?

For BryanJ: 
some photos of the camshaft, No4 Ex valve lobe.
To the outside edge of the lobe is an unworn ridge; I tried to phot the profile, inthe second shot you can see the raised edge.
the Lobe/cam height measures:  34.32mm (1.352") versus nominal 1.360" and bottom service limit of 1.356".
Then the No4 Ex valve rocker follower: 
you can see a slight 'flat' across the centre portion of the follower; that's probably lost a thou or so (?);

so in total that's say 5-6 thou' lost valve lift (bottom limit case; nearly ten thou' on nominals.

- I guess it could be much much worse?
but I'd welcome your opinion on my options.

AndyC

[UK Pete]

Hi Andy, i bought the neway cutters, they come up on ebay here and there or send of and buy them from USA , the head i did in that post was a Kawaski Gpz550 head, as this is the bike i am restoring at the moment, but they will also do my cb750 heads when i get round to it
Pete

[Bryanj]

That Cam is shot due to lack of oil, look at the bearing surface on the end.

Also check wether the rocker spindles that are in the cover have worn the cover oval, this can happen  although I've only seen one.

Still reckon your cheapest repair is a replacement head as guides and machining will be well over £100 plus £80 for pattern valves.

Camshafts and covers do come up on ebay---don't forhet the USA BUT remember there is only airmail now---Unless you plan on a holiday or know somebody who is

[matthewmosse]

California Connection / AP incorporated inport US bikes and often have engines, last time I needed one it was £150 for a unknwn quantity engine or £300 for a tested one plus £60 for pallett delivery so I had 2 unknowns to make the best of the deal - one was mint to look at but kept eating tensioners so wound up with bent valves - never did find out why. Other is in my 500. Given ebay prices at the moment I'd look at a complete engine from them if available and if the price is still in that ballpark.

[andy_c101]

I'm hoping to pick up a camshaft off of fleaBay.
& I've ordered valves n guides off CMSNL (D/Silver didnt have the full sets)

I managed to extract the valve guides (I pre-heated the head in the oven at "60" for ten minutes - like we do to 'warm the dinner plates'; .... shhh don't tell you-know-who!)

I have a question (request advice) regarding cylinder/bores. 
- I've used a bore dial gauge to measure each bore, tdc/bdc/mid-stroke, in a couple of places (each cylinder), and all measure within 58.50-58.52/.53mm (within service limit of 58.60mm);
piston ring gaps (side & end) all measure within service limits;
So my question: What would folks on here do/recommend?  - just rebuild as-is? or renew rings and/or more?



Andy C