Chevette Owners Group
Non Members Area => General Discussion => Topic started by: Allanchvet on Feb 17, 2017, 15:43:17
Could someone recommend a good garage or someone to carry out a top end rebuild on my standard Chevy. Suspected inlet valve seal wear.
What would be a rough cost? Not sure but may be worthwhile doing the piston rings too if the head is off anyway.
I cannot answer the question sadly as down south, however the valves are usually pretty resilient on these and i do 1-2000 miles a month in mine.
What i do find is the tappet clearances do close up on some valves over time, most likely due to unavoidable seat recession in hard driven pre-unleaded engines. Setting them a bit wide delays this issue , something like 13 thou or so (0.3 mm) .
@Mad Max A.K.A. Mal is / was nearer you so may know some local engine shops though if that is no help.
just re-read your message, you said valve seal :D , doh!
You may find a workshop with the kit that would mean they can change the valve stem seals without taking the head off. i.e. able to compress the valve spring/hold the valve up via some means like an air bag through the plug hole or something.
would be a lot less hassle than having to take the head off. Although if the engine is old and the head gasket original then there is a good chance it will fail at some point anyway :(
Scotty did mention the seals could be changed with the head in place but as I'm not certain the seals are the issue and following advice on here, I'm just going to take off the head, inspect it and go from there. I'll post up some pictures for yous knowledgeable guys to look at and advise once I have the head removed. If necessary I'll probably have a go at changing the seals myself.
Hi. Do you have a compression tester /borrow one? Would be a good starting point before getting involved. Also if burning oil, generally if accelerating and you see smoke this normally means rings if none seen but as the engine slows (still needs to be driven to see) and you get smoke that would indicate valve stem oul seals. Hope this helps.
Yes I've carried out a compression test, showed good results, Approx 130psi on 1&2 and 140 on 3&4 with no change adding oil to the cylinder. I haven't driven on the road as no MOT, only up and down the drive at low speed but just seems to smoke constantly idling or higher revs.
Think the next move is to get the head off.
If its smoking continuously and it doesn't vary with engine speed / throttle action its very odd! I had something similar when I fitted a new exhaust to a motorbike once- it turned out to be a exhaust manifold air leak caused by a broken stud in the end.
Is the smoke blue? Does it smell( of oil or fuel or antifreeze) Are you losing water? Is it the same with the original carb on? Does using the choke do anything? Is it the same hot and cold?
Yes it smokes all the time, fine on initial cold start then it changes once its just getting warmed up. Using choke/revs don't make any difference. Also adjusting carb mix did nothing either. I tried to swop over the old manifold and carb to eliminate a possible leak at the intake but due to modding the connection for the servo to fit your manifold, I couldn't remove it from your manifold without cutting it again so no vacuum to draw the fuel through. I might have another go at swopping back to the original set up. I can maybe borrow the standard servo connection from my mates Chev. (He has just pulled it out of the barn after 20 years! Needing work!).
The smoke looks grey blue/cloudy. I think the water level had maybe dropped a little last time I checked but doesn't smell of antifreeze. It looks to me like oily water being emitted, now seems worse than it was initially.
Like to say sorry to everyone for clogging up the forum with this annoying issue! Really need to get it sorted :wallbang:
Just put the original msnifold on and blank off temporarily the vacuum connections and just connect up fuel to get the engine started. All thats needed is to eliminate the new carb / manifold as the source of the problem.
From what you have said today about the smoke I think its likely that all you need to do is change the head gasket after decoking the head and pistons. Don't bother with skimming as being a cast iron head it is unlikely to be warped. No need to grind the valves either. - Scotty
You could maybe try the test again when hot as this would maybe show up any coolant getting into the cylinder. The colour doesn't sound oil more like the h-gasket or bad fuelling. The joys of cars!!
I'll fit the original set up back on tonight, at least the manifold and weber can be ruled out then. I should get vaccum this time (nicked the servo connection off mates Chev). Couldn't find anything suitable to blank it off last time.
i think i put a video up of when this happened to my chevette. you get what looks like smoke out the exhaust but is fairly white. It is water vapour basically.
The most common failure on the 1256 is the head gasket , especially between cylinder 4 and the water jacket. As a high mileage driver of these beasts i have had that happen three times now .
They also fail from age as the gasket thins, the head tension reduces and coolant seeps into the gasket, rotting it. the combustion chamber gasket rings also rot away, exposing the gasket to the full force of compression.
The last HG change i did i took heed of some advice i found on google and before fitting the new gasket, i brush painted it with wellseal, a liquid gasket compound. far better and easier to use than hylomar.
you brush it on both sides like paint (use a good paint brush or non fluffy sponge etc..) , let it evaporate its solvent a while then fit it to the car. It is sticky stuff so avoid getting dirt and crap on it before fitting too.
I used one of those household paint / paper removal scrapers that you can drag backwards (has a rigid handle/blade) to clean up the head and block surfaces too prior to fitting.
so far so good some 10k miles+ later :)
Interestingly the original replacement GM gaskets for the chevette were also coated in a sticky stuff so it seems this was the done thing .
the wellseal should keep the corrosive/damaging coolant and oil away from the gasket and as it is non hardening should keep the head sealed nicely .
I also initially torqued the head evenly in stages from 60nm to the recommended 76nm (i think) and went past that to 80 as a final.
Make sure the head bolt holes are clear and the head bolts threads are clean too. brake / clutch cleaner aerosol helps here as does pressurised air :)
Also make sure no bits of old gasket fall into the oil way that goes from block to head . stuff some rag or kitchen roll in that hole while working on it.
if crap in there gets pushed into the head it will block the small oil ways that lube the rockers.
cylinder 4 to water jacket failure on my yellow hatch.
it was a generally unwell gasket.
That gasket has seen better days! Intrigued to see what mine looks like! I'll follow your step by step for changing the head gasket.
Before you take the head off, just run the engine and spray WD40 around the inlet manifold and see if you get any bubbles or patches where air getting in. I had this problem when i fitted my manifold first time i did it. The bolt are pretty long and the silly middle bolt that's inside the manifold i locate it in just in case?? I think the original manifold needed a skimming to make it perfectly flat again. If the car be sat for 20 years the water pump may be rusted up. A new waterpump and a few flushes with a dishwasher tablet will do a great job cleaning it all up.
No not mine, its my mates car that has sat untouched for 20 years.
Yes that middle bolt on the manifold is a right pain! I bolted back on the standard manifold and carb, plumbed it all up. Car started, idled fine, same issue, as soon as it starts to warm up - Smokey Joe!
I checked the manifold when all this started, spraying WD40 and listening for leaks - Nothing.
Thinking it is the head gasket. I drained the fresh coolant I put in recently, looks dark and oily. Started removing pump/fan assembly, try and get back to it on Sunday. Mate says I should be doing a leak down test first but I'm just going to crack on and get the head off and inspect it. Makes sense to inspect the seats when its off I guess so might need the spring compressor Scotty.
Pic below, took a video too but can't upload it to stupid photobucket.
With a leak test it will tell you if the pistons rings are ok? If there no air coming from the dip stick rings should be fine. If no air from the oil cap then its the head gasket and the valves are fine me thinks???
Yeah carried out one on my previous bike but it was definitely drinking oil! Valve stem seals were worn. Fingers crossed Chev is just the head gasket.
Head off, managed to shear 2 studs for the manifold, thought the whole stud was loosening :wallbang: Pics below, head bolts were all tight, gasket looks fine, fluid sitting on top off the pistons, bit red like the classic oil I put in it. Certainly doesn't smell off fuel, what now? Rings worn! Advice please.
Looking at where that fluid level is, did you not drain the coolant from the block before removing the head?
There is a 7/16 headed plug just behind the alternator on the block for that purpose.
Head gasket sealing rings don't look too clever between cylinder 1&2 and 3&4.
Pistons and bores of 1&2 look very clean. Given how black the black the head is suggests it's been running very rich. So well worth the removal in order to clean all that.
Now the head is off I think I would go down the route of unleaded seats, valve guides (if and where required) new stem oil seals and a skim.
Ah yeah, Ashley, forgot about that drain plug for the block but tried to remove it before to flush the system but could not get it to move! Extremely tight and starting to round the bolt head so gave up.
Okay guess its worth doing it properly setting it up for unleaded. A bit beyond my skill level, I'll see...
Whats the best method for de-coking the bores and everything?
Interesting pictures! The bores look OK so provided the non -wear lip at he top isn't too big no need to rebore. The gasket is well knackered. I can see that it has been leaking between 3 and 4 and probably to the water gallery there too. So that's the likely cause of your problems. Your choice is whether to just fix the gasket or do a full head recondition whilst its off. Depends on money really. If it was me I might just decoke the head and piston tops change the valve seals to get running again quickly and cheaply and in slower time get another engine and rebuild that fully. Again that depends on what sort of work space you have available.
When decoking the pistonheads don't try too hard to get the edges shiny or remove the coke from the bore top lip as the crud there helps the compression. Just put each piston to the top and clean off the surface black.
As the engines compression was so good you shouldn't need to grind the valves either just get the black off then and change the inlet seals.
Change the oil before restarting as it is now contains water .
Thanks for the advice again guys! Think I'll just get it fixed up as you suggest Scotty - Clean up the head, change the valve seals and follow Bills method for refitting. Is the spring compressor in the post Scotty?
Yes it is.
Update: Head is in at a local place in Paisley being pressure tested - Glasgow Grinders (And no I didn't come across them whilst googling that. :))
If all good, skim then may as well go the full hog and get the seats replaced for unleaded, not that bad price wise at £80 quoted.
In their quote they recommend replacing the guides too. Is this necessary? or best to inspect them, need to check the manual later, maybe a tolerance for wear to work from?
If you replace them you should fit new valves really. And new springs probably. Then you have a reconditioned head more or less. - Its all about cost as the car won't run much different whatever you do. - Scotty
If your going to get the valve seats unleaded, then you may as well have any worn guides replaced too. No need to replace any valves, any good engine shop will just recut and lap in your existing ones.
I ended up using another company to do the work and decided against going down the unleaded route. Head was pressure tested, skimmed, oil stem seals replaced, seats re-cut and all the manifold studs replaced. Looking shiny!
Try and get it back together this weekend.
That's a clean looking head! Hope the reassembly goes well. I am a bit intrigued by the use of studs for the exhaust manifold . Bolts were normally used by Vauxhall. - Scotty
Looking good, was there any feed back from the firm that did you work? Valve recession etc??
The valves seem to be okay, no mention of recession. He said the valve seats were showing a bit of wear. Work done was not so much as re-cutting, he just "tickled them" as he put it.
Should I use any sealant when fitting the water pump assembly with the new gasket? Also needing a bolt for the assembly mounting, any ideas on the bolt spec and where I might get one?
A smear of blue hylomar or similar on the gasket won't hurt. As for the bolts - they are not Metric - UNC maybe. Take one of the remaining ones to your local fastener place (ours is ALLFIX) who will be able to identify the thread and may even have something suitable. - Scotty
1/4 unc is the thread size. 5 bolts are the same length, the 6th is quite a bit longer.
Don't forget a suitable gasket sealant is required on the head gasket too around the pushrod area. Stag Wellseal is my sealant of choice for headgaskets and sump gaskets.