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Cvh Piston Numbering & Uneven Bore Wear Questions...


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Copied from my resto post, may get more attention as a seperate thread in the right section...

 

 

 

it looks strange in there, the faintest of faint cross-hatch marks left on the bores but with a small lip at the top of pots 1 2 and 3, not enough to catch a nail in but pot 4 is where it gets scary...

 

There's quite a pronounced lip, but it's only on the sides of the bore (i.e. the NON thrust faces, along the line of the gudgeon pins), the front/back of the bore are same as the other 3. Also was noticeable play left to right with the piston at TDC. What could have caused excessive wear on the side faces like this? only things I can think are crank endfloat (negligible) or a bent rod (also unlikely IMO as the piston sits equal height to it's opposite number).

 

Also I noticed the pistons are stamped with numbers, only issue I have with that is that from gearbox end they're numbered 2, 2, 3, 4... it has 2 pistons marked number 2 :/ were they numbered from the factory (meaning I have a mixed bag of pistons/rods) or could it be that a rebuilder just made a mistake when numbering up?

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That's my thoughts too, although from the service/repair manual I found online I'm hazarding a guess that the numbers could be standard size variants. Gasket set and bolts arrived yesterday though & seeing as it was running reasonably and with even compressions prior to me stripping it (mainly for cleaning access and to have a "look see") I think I'll probably throw this lump back together and get it running as well as I can & start hording parts to build a zero-mile gooden. I did see some 1mm oversize pistons for about £230 the other day but will have to see what state of block/bottom end I can get hold of as a base.

 

From the play in #4 piston I fear even a 1mm over bore wouldn't save this block, although the only oil it seems to have burned is from stem seals.

 

That brings me onto another question, the head set I have came with 8 top hat type seals but all the engines I've worked on in the past, bike/car/air/watercooled or whatever, only had seals on the inlet side. Is this a packing oversight (bearing in mind how many engines are 16v these days) or should there really be seals on the exhausts too?

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Yup. Seals are on all of the valves. Smoke like crazy when they are knackered.

 

You would be surprised how big a 1mm oversize piston really is in a bore. Normally they are in tenths of a mm. Are there no sign of blow by gasses on the piston on no 4? If not the play may not be as bad as you think. Remember the piston will be a tighter fit when the engine warms up. I would decarbonise and measure for ovality.

It is true that the numbers could be grading marks but I don't remember seeing any on a CVH before. I do know that the con rods and caps are marked 1234. Also the rods should have f on them to face the front of the engine ie cam belt end.

Nothing more satisfying than a good engine build? Have fun!

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You could well be right, it feels scary enough with a cold engine and catches my fingernail well enough but it could turn out to be not as bad as expected.

 

I found out the stem seals are on all 8 like you said, last night as I got a minute to strip the head. The original type seals were, all but one, sat halfway up a stem & all as hard as rock so it'll be a definite improvement with the new ones I have, built into the spring seat.

 

Good point on the blow-by since there wasn't really any breathing going on, and only smoke was stem seals so I may just be being paranoid on the bore wear with it being worse on one pot than the rest. Not dropped the rods/pistons out as I'm planning to run the engine this summer (on the basis that it's held together last year when it got a beasting) and then pull it apart properly when the salt comes back out and see what the real score is...

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Just a thought. If the valve seals were that bad then the oil dripping down the valve and burning could have made a really hard bleach deposit around the bore making it look like a lip. Sure its not just that? Try scraping it off with a solid knife. Steel wont hurt the bore.

 

And yes the new type seals have the bases built in. This is to stop them riding up the valve. Throw the old ones in you Box of bits and bobs!

Regards

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Nice call, sadly it's definitely a wear lip. No big deal though, I had toyed with the idea of a fresh build anyway even before seeing inside.

 

Those original stem seals have gone where they belong, in the bin! They were that hard that it'd be no exaggeration to say if you hit them with a hammer they'd shatter...

 

On a positive note, valve heads soaked overnight in Gunk+ (never tried the stuff before, I've always preferred brake cleaner but could only find it in aerosols this time) and the inlets have come up like new, exhausts have some burnt on deposits/whiskers from the oil burning but I never expected it to shift that anyway lol either oven cleaner or elbow grease for them. Overall I'd prefer something non water-based as I could use it on internals more safely but it does a good enough job on individual bits & exterior of the block/bellhousing etc.

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Hmm well, I can safely say that Ovenpride does very little to shift burned on carbonised oil deposits from exhaust valves lol. They are pretty awful though, where the inlets are waisted the exhausts are bellied by about 1.5mm from all the crap on them! If nothing else it'll breathe a bit better when it's back together!

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Only reiterating what been said ...Yes stem seals on all eight valves and the stamp numbers on pistons are likely the factory size options each piston available will have multiple size variants to cope with poor manufacturing processes cutting bores...if this as the same as most engines I've played with car and bike..

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Are you changing the hydraulic tappets/lifters while you are in there..I did my seem seals recently and for the sake of 30 quid changed the lifters while I had the rocker arms off it quietened down the too end considerably....OK it doesn't account for super soft cam lobes but I was only doing the seals and thought why not ...

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Nope, lifters are actually some of the quietest I've heard on a CVH so they're staying for the foreseeable... New possibly when I build an engine though. Cheers.

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Yeah I think they must work for a few years, otherwise they'd not have sold very many. The engine seems to have been well cared for by its one owner but stood for many years so maybe the bore wear is down to corrosion worn off when the engine was started again. Will update on how it runs when it's back in one piece, should be a lot better the amount of crap I got off the valves, and the exhausts look in dire need of grinding in. I bet they were leaking like a sieve before!

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  • 2 weeks later...
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Well the car is running again although not completely finished, and what a difference already. Prior to this mini-overhaul I found it impossible to set base idle but now its simple & the engine appears to start a lot easier (this maybe down to the cleaned/lubed starter spinning faster though).

 

Jobs still to do are refitting the PAS pump/alternator & bracket, exhaust manifold/downpipe join, rad/fan and header tank properly mounted, servo & master reinstalled and maybe renew the crank sensor as I feel it's a bit iffy. think that's about it but had to call time on it as we're off to see my mother now... Hopefully theres enough light to finish it later though and get a quick drive with the top down before it goes cold.

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