Head-off job looming; distilled wisdom sought

[hatman]

Been aware recently of oil-in-radiator syndrome on my big-valve twinc. No mayonnaise on oil filler cap though so hopeful (ever the optimist!) that it's merely one-way traffic, besides, the car's been running fine.

However, after a bit of track-situation hard driving last week the engine was only running on three on tickover and low revs when I drove home but cleared its throat and got on with it when I put my foot down a bit.

Subsequent examination reveals that number four ain't doing its thing, at least on start-up and low revs, although the plug's dry and the right colour. It also sparks fine when laid on top of the engine, leading me to think I may have valve problems rather than electrics.

I now accept that the head's got to be pulled. Other than the obvious (new gaskets, possible skim) is there anything else I need to be looking for or taking advantage of whilst I'm in there? All thoughts/experiences (bitter or otherwise) eagerly awaited and will be weighed, considered and acted on (I'm a first-timer in the twinc head-removal game).

[rgh0]

Best distilled knowledge for rebuilding a standard head in the workshop manual and Wilkins book

Other specific things I do for what its worth.

Always replace the guides with modern aluminium bronze or copper-silicon-nickel or equivalent material guides they are much better than the standard cast iron.

Inspect every component very very carefully for wear or distortion versus it specified dimensions and tolerances, you need access to good quality measuring equipment and know how to use it.

Put in new valves or crack test the existing valves if reusing them. One dropped valve head will destroy an engine.

If you come across any problems not covered by the books during the rebuild I am sure the list can help.

Rohan

[david.g.chapman]

I had a problem in the past with burning exhaust valves.

I would always make sure there is a good 1.5 mm or more ring of valve to seat contact when you have ground in your valves. It helps to keep them cool

Dave Chapman.

[steveww]

As always Rohan's advice is spot on. If the head is off anyway I would double check the water pump, may be replace it just to be sure. It would be a real pain having pulled the head and refitted it only to have the water pump fail shortly afterwards

While you are in there a new timing chain is always worth fitting and possibly the sprockets as well. All depends how worn they are.

Useful tip about the size of contact valve to seat on the exhaust, thanks.

[gjz30075]

Inspect every component very very carefully for wear or distortion versus it specified dimensions and tolerances, you need access to good quality measuring equipment and know how to use it.

Rohan

Put this sentence to good use on the cam buckets and their bores. If the buckets and/or bores show any wear, the buckets start to rock and the skirts of said item start coming apart.

Greg Z
'72 Sprint

[john.p.clegg]

Before you pull the head you might want to do a compression test?

John

[elansprint71]

Absolutely right Cleggy- do a compression test and be advised that all the grunge from the sump breather tends to go into cylinder #4, chuck some Redex into that cylinder and do what it says on the tin, + squirt some through the carb into that cylinder too.

Cheers,
Pete.

[hatman]

Plenty of food for thought there chaps, particularly your possibly pre-emptive thoughts John and Pete - thank you. I'll be out there with the compression tester first thing!

[rgh0]

If the compression test shows No 4 is low it is then worthwhile doing a leakdown test and carefully listening for where the air leakage is coming from - inlet, exhaust or past the piston into sump this will help guide you during the rebuild.

When checking cam followers and sleeves you need to check top, middle and bottom. The followers wear into a barrel shape and the sleeves wear into a hourglass shape. A lot of people do a quick check in the middle of each and get an in tolerance result and then wonder why the followers produce a tapping noise on rebuild as they rock in the sleeve bores.

Rohan

[twincamman]

check the plug wires I had that happen ---one wire was shorting to the block near the distributor -- -ed

[hatman]

I checked the leads first thing Ed - all hunky dory there. Is a leakdown test a garage activity Rohan? (ie we're talking specialised equipment I imagine).

[twincamman]

a leak down and a compression test equipment are a little different ----try the compression test first it will tell if there is a problem with the compression only;---- a leak down test will detect what valve intake or exhaust or rings by the sound --- compression s. b. around 180 lbs -but look for Even readings all across the 4 cylinders --pulling the head is not a huge job---20 to 30 minutes after a few times [ an hour the first time -]---putting it back is easy too --its just a pain if the thing works well to disturb everything and reset it up ---- are you sure the idle screws were around 1 and 1\4 turns out when hot ?----- --ed

[marcfuller]

the head's got to be pulled. Other than the obvious (new gaskets,

If you can get a machine shop to surface the head smoothly enough, I would suggest you look into using a newer tech MLS (multi-layer steel) head gasket (like COMETIC makes). These MLS type head gaskets seem to "cure" the problems of sealing aluminum heads for the long term.

The reason you need a very smooth surface on the head, is that the head moves about 1.7 times more than the block and will grind the MLS gasket down if it has a standard surface smoothness.

[hatman]

Looked at the link Marc - thanks. The blurb looks impressive enough (they all do, don't they?) but what's the feedback from the real world like? Are you using their stuff? If so, what's the verdict?

[marcfuller]

what's the feedback from the real world like? Are you using their stuff? If so, what's the verdict?

I think they are significantly better than the copper type head gaskets for our T-Cs and worth the addtional cost. This is only if you can find a shop which can put a smooth finish on your head (50RA or smoother)

I will be using one when the head goes back my engine on in the next week or two. Keith put up a post on them last year and there have been some other. Since then I have found the MLS gaskets are used commonly used in situations with iron blocks and aluminum heads, high compression engines, and for warranty repair by GM and Chrysler on their aluminum engines that are prone to head gasket failure.