Head Bolts

[SteveW]

Don’t know if this is relevant but I recently rebuilt the top end of my 1980 650 engine.
I found that the replacement head gasket was 0.1 mm thicker than the original and the new o-rings for the oil feed to the cam were 0.4mm thinner than original.
So a total of half a mm under size.
I wasn’t going to risk it leaking so I sourced some o-rings half a mm over size and no leaks at all in 200 or so miles.
The gasket set was NE brand from David Silvers.

[McCabe-Thiele (Ted)]

My 400 engine rebuild including a rebore came out at around £1200 for parts that included new threads for the cam chain tensioner bracket - shells big end.mains, both chains, primary drive bearings, drive rubbers plus some gearbox parts. Rebore by Trigger. Gaskets etc.

[Laverdaroo]

If you’re that worried, just take the top off and see if there’s damage and or check for warm on an engineers plate or a bit of glass
These motors aren’t that complicated, especially after working on ducatis and other European temperamental lumps. The crowd on here have your back and you shouldn’t have a worry doing it. If you can work on a trumpet you’ll breeze the 750 motor. It’s not one big job, it’s just a selection of little jobs. Easily said but keep telling yerself that and the nerves will go. Go for it, it’s really satisfying. Don’t forget though it’s a 40 odd year old bike, they can’t run brilliantly all the time, you’re the new custodian, make it how you want it and don’t be scared or apprehensive about it, it’s not as hard as you think. Just follow the process and you’ll be away


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[Bryanj]

Is the manual you have Haynes, Clymer or genuine Honda?

[Martin6]

Honda (downloaded) and Haynes.

[Bryanj]

I will admit that the Honda one can be a bit daunting to the novice as it a direct copy of that supplied to dealers for qualified mechanics so it may not include the bits we think of as basic so start with the Haynes BUT they do make mistakes so cross reference important bits with the genuine, and you ask on here for anything you ae not sure of we are friendly bunch, with odd bad days and even odder sense of humour!

[Matt_Harrington]

I haven't seen the Clymer manual for the 750 but I really like the one for the 400....

[Martin6]

I used the bike again yesterday. I ended up doing 120 miles with a mate on his modern Z900RS. The Honda kept up without complaint. By the end of the day there was a misting of oil on the side covers, my boots, fins and the top rear of the engine case. But the bike ran well and the oil level hasn't noticeably dropped. So, whilst I'll monitor it, I plan to ride it this summer and Autumn, before I sort out the weeping head.

👍

I think I'm going to have to do something about the suspension though. Too bouncy, front and rear, on my local roads.

[Martin6]

Planning ahead for my engine out amd strip: Encouraged by your comments, i will attempt it myself, with some help to lift the engine out.
I have the Haynes and Honda manuals and have watched a few YouTube videos to familiarise. I've ordered an engine stand, so I can work on a workbench. The bike has done 41,000 miles. I have nothing to suggest the angine cases have ever been apart before. I'm thinking I'll go as far as replacing the cam and primary chains and anything rubber (seals and chain tensioner rubbers).

- I already have a full gasket set from David Silver, are these good enough?.

- Are there any 'special' tools you would recommend me to get hold of?

- From your experience, are there any other parts I really should replace, regardless of apparent condition?

Thanks 👍

[Bryanj]

Clutch nut peg socket, 3/8 drive torque wrench, set of 3/8 drive six sided sockets, impact screwdriver with JIS bits.
Remove points plate and advacer before lifting out and be careful not to bend the stud.
No need to remove generator rotor unless you have starter problems as no crank seal that side, oh and you need a set of seals for the engine

[Martin6]

Update: I've posted various questions in other posts, along the way. I'll stick to this thread in future and thought I'd summarise progress.. I'm sorry it's a bit long. Also, please let me know if you see mistakes I'm making 👍.

The engine is out. Head and barrels off.
I found significant damage, beyond repair, to the gasket surfaces between the head and valve cover, where it had been jemmied off at some point. This was definitely one of the leak points. Gouges were deep, across the entire width of the gasket surface, including around the screw hole. A difficult repair, which i would have to put out for welding (if possible). I decided to find a replacement head and cover. I have found a 2nd hand replacement head (with valves) and a cover. They appear to match. Slightly different casting shape on the head's bottom cooling fins, but the gasket face, bolt and stud holes etc. are identical. I've been through the replacement head, thorough clean and compressed air, except for removing the 2 oil metering plugs. With the valve stem oil seals removed, there was a small amount of play in the axhaust valves / guides. I looked at the original damaged head and this was no different. It wasn't burning oil, so I will go with the replacement's guides and valves. Lapped the valves, new stem seals. I think it will be fine. ( after reassembling the valves, springs etc., I realised the springs go in a particular way round, tight coils at the head end. So I've had to do it again!)

I checked the valve timing before I started to remove the cam / tappets. It was out by one tooth of the cam sprocket. When the cam was at TDC, the crank was at 'F' on the points plate. Thankfully, there was no sign of piston to valve contact.

The bolt which is front centre, outside the cylinder head between exhaust 2 and 3, had indeed sheared. It is broken off at a point too deep inside the barrel casting for an eazi-out.

The cylinder barrel: All 4 cylinders were shiny, showing no sign of honing / cross hatching. There is a slight lip in the top of all 4 cylinders. There was carbon on the piston crowns, and the crowns have some wear (a couple have swirl marks, particularly no.2) but no damage. The rings were replaced 2,000 miles earlier. They were free and clean. Looks like the cylinders weren't honed for the new rings. The carbon on the crowns came off easily with brake cleaner and scotchbrite.

The cylinder barrels are now with a local engineering shop recommended to me. They will remove the sheared bolt / check the thread and believe the cylinders will be ok with a gentle hone / deglaze. I will check rig gaps, before reassembly.

I checked the primary chain from inside the sump, the tensioner is within spec at 68.24mm. The cam chain tensioner has plenty left and the chain does not appear worn, it was tight to get off the sprocket (tensioner removed) no tight links and resists 'lateral' movement. I think it's fine. The tensioner rubbers also look ok.

So, I am planning to leave the crankcase undisturbed.

In the cylinder head, I would like to remove the oil metering plugs and clean behind them. Compressed air does blow through ok, but I'd like to check. They don'twanttocome out. Is there a technique to removing them without destroying them?

Committed now! Much to learn. Advice gratefully received. Thanks.

[Martin6]

The cylinder barrels are back. Light hone and broken bolt removed. I've measured all the dowel clearances and they look fine. I'll be using the David Silver supplied gasket set. I will check the o-rings match the gasket thickness. Which o-rings is it that are potentially too thin?

Once I've cleaned the bores and oiled them, I think I'm ready to reassemble. I'll follow the book. Haynes and factory, although both seem to focus on earlier top ends. I'll aim to put the cylinders and head on today and torque it down. Mine had loose nuts and bolts when I took it apart, so I'll leave it overnight and check the torque again, before moving onto the cam and valve gear assembly. This is a first and I'm nervous 

- Are there any tips you would give?
- I've seen mention of applying a light coat of gasket sealant to the plastic / rubber pucks. Is that a good thing to do?
- gasket sealant anywhere else? It seems odd not applying anything to the gasket surfaces at the base of the barrels and the head.

Thanks, Martin

[Martin6]

Hi, My gasket kit does not include four O-rings. Those that go around the studs either side of the rear of the cam chain tunnel. I think it is 2 between the crankcase and cylinder block, then again 2 between the block and the head. My old ones are distorted, but are about 16mm ext dia, to give a rough idea.

Does anyone have the right dimensions for the rings and a good source?

Thanks, Martin

[Pauarc]

Hi Martin
Part fish for head
Paul

[Martin6]

Hi Martin
Part fish for head
Paul

Well done, thank you. 11mm x 2.5, = 16mm o.d.  Must be it.

Appreciated.

Martin