Author Topic: pistons to far above deck (Read 3920 times)

thomcat · « **on:** March 12, 2009, 05:28:42 pm »

Hey gang Can i get away with pistons .044 inch out of the block? I have a fresh bore and pistons and the dock is decked so all is tight and true. is there another option for headgaskets(1.6 na mechanical) or do I have to pull the rod and pistons and have the crowns faced off?
Thanks Thom

Smokey Eddy · « **Reply #1 on:** March 12, 2009, 05:35:07 pm »

Quote from: "cyrus #1"

According to the Bentley:

Mechanical Engines:
- 1 notch - 0.67-0.80mm
- 2 notch - 0.81-0.90mm
- 3 notch - 0.91-1.02mm

Hydraulic Engines:
- 1 notch - 0.66-0.86mm
- 2 notch - 0.87-0.90mm
- 3 notch - 0.91-1.02mm

0.044 inches is 1.1176 millimetres.

I think that would REALLY be risking it... Maybe you could stack two 1 notches? hahahahah I dunno man. Maybe you have to get the crowns taken down... at least it wouldn't have to be much.

the caveman · « **Reply #2 on:** March 12, 2009, 06:46:39 pm »

I would double check those measurements and if they are right then the pistons will have to shaved.

bigblockchev · « **Reply #3 on:** March 12, 2009, 10:03:46 pm »

You might be able to have the bottom end of the conrods resized to compensate for the extra deck height. The mating surface of the big end is shortened and the hole is resized to standard thus shortening the centre to centre length. With the small discrepancy it should be possible. Another possiblity is to have the crank destroked by offset grinding down to the next smaller journal diameter. Be sure to get a real good machine shop to do these as they are a bit more complicated than the usual. Or just get another block. Cheers Dan

Rabbit TD · « **Reply #4 on:** March 12, 2009, 11:23:19 pm »

Quote from: "libbybapa"

How much did they deck the block??

I would certainly have the pistons shaved prior to fitting two headgaskets (that would double the odds of headgasket failure). The KS pistons have a coating and so the option of shaving the tops and removing the coating is not at all appealing to me. The top mating surface of the rod big ends could be shaved and the big end re-bored as, IMO, a more attractive alternative.

Whenever I've had new pistons fitted without decking the block, the piston protrusion has decreased. I presume that oversize pistons move the pin closer to the piston crown purposefully in order to accommodate milling the deck. The process to avoid such difficulty from over-cutting the deck is to have the cylinders bored and then fit the crank rods and pistons. Then measure piston protrusion to get the baseline. Then remove crank/rods/pistons and do the match in order to tell the machinist the maximum amount of material that can be removed and still remain within the spec for piston protrusion using the 3 notch gasket.

That's the way my pistons were that I got in my rebuild kit {King Brand} from Parts Place. They had exactly .005 less heigth which worried me at first but then realized they probably did that to allow the deck to be milled which I did. It put me right in the middle range of a 1 notch fiber gasket.

jtanguay · « **Reply #5 on:** March 12, 2009, 11:26:16 pm »

i suppose maybe this is where those custom head gaskets might come in handy? but that would really suck having to buy a $100 gasket each time you pull the head...

Rabbit TD · « **Reply #6 on:** March 12, 2009, 11:32:19 pm »

Quote from: "jtanguay"

i suppose maybe this is where those custom head gaskets might come in handy? but that would really suck having to buy a $100 gasket each time you pull the head...

I think I would go with the custom gasket first if you can get one for around a hundred dollars, I have no idea what they cost but that is a lot cheaper than the other alternatives if they are around that price.

bigblockchev · « **Reply #7 on:** March 13, 2009, 11:58:33 pm »

It strikes me that shortening the conrods has got to be cheaper than custom headgaskets every time. You would then be back to std gaskets forever after that. Cheers Dan

Rabbit TD · « **Reply #8 on:** March 14, 2009, 12:48:46 am »

Quote from: "bigblockchev"

It strikes me that shortening the conrods has got to be cheaper than custom headgaskets every time. You would then be back to std gaskets forever after that. Cheers Dan

I wonder what the going rate at the machine shop is for something like that, did you ever hear? I imagine you would have to use a rod bearing with a bigger od. also wouldn't you and are they available to do this. I'm just curious about this incase i ever have to consider it myself sometime down the road.

Patrick · « **Reply #9 on:** March 14, 2009, 08:36:53 am »

I think standard practice for this would be to push the bushing into the rod and then ream it to size, all they would have to do is cut it off centre if there's enough material. Last time I had rods rebushed it was about a hundred bucks a rod, bigger engine though.

sdwarf36 · « **Reply #10 on:** March 14, 2009, 11:09:43 am »

Although I havent hopped up a vw diesel (yet), I have worked as an automotive machinist for 25+ years and am currently working in a performance engine shop. There are certian things you can/can't do.
Re-bush the small ends: everything works off the center of the original hole-so that won't help.
Machine the big end of the rods: well you could cut more off the rod end rather than the cap before you hone it back to round-but the gain will only be a couple of thousandths at best.
Offfset grind the crank: you end up losing stroke-and you only will lose 1/2 of what you grind off the crank (.020 grind will put the piston down .010)
Headgasket : best option. Contact Cometic gaskets-if they have a pattern for your motor (and i bet they do) they'll make a gasket in any thickness you wish. Maybe $100.
Doubling up head gaskets: we do it with .015 steel shim gaskets at times on Chevys--but dunno about holding back a diesels compression. And you can't do it with a multi-layer gasket.
Cut the top of the piston: quick + easy if your worried about coatings, get it recoated.

jtanguay · « **Reply #11 on:** March 14, 2009, 12:01:49 pm »

maybe going the $100 headgasket route will be the easiest/cheapest option? seems like a lot of work either shaving pistons, or messing with the bottom end (all new rod bolts cost a bit...)

gldgti · « **Reply #12 on:** March 14, 2009, 06:17:04 pm »

why not get a FOUR NOTCH (yes, 4 notch) head gasket?

they are available from some suppliers for just this reason - my dad needed one on his 1.5 after rebuild...

given the bore of the 1.5 is the same...you can use same headgasket too.

heck, if we can buy vw diesel 4-notch headgaskets here in australia, i reckon you MUST be able to over there :-)

jtanguay · « **Reply #13 on:** March 14, 2009, 09:29:25 pm »

Quote from: "gldgti"

why not get a FOUR NOTCH (yes, 4 notch) head gasket?

they are available from some suppliers for just this reason - my dad needed one on his 1.5 after rebuild...

given the bore of the 1.5 is the same...you can use same headgasket too.

heck, if we can buy vw diesel 4-notch headgaskets here in australia, i reckon you MUST be able to over there :-)

i thought the extra thicknesses were only available for the 1.5 engine? and that 1.6's only had 3 notches, as well as the 1.9's.

Turbinepowered · « **Reply #14 on:** March 14, 2009, 09:46:22 pm »

Quote from: "jtanguay"

Quote from: "gldgti"
why not get a FOUR NOTCH (yes, 4 notch) head gasket?

they are available from some suppliers for just this reason - my dad needed one on his 1.5 after rebuild...

given the bore of the 1.5 is the same...you can use same headgasket too.

heck, if we can buy vw diesel 4-notch headgaskets here in australia, i reckon you MUST be able to over there :-)

i thought the extra thicknesses were only available for the 1.5 engine? and that 1.6's only had 3 notches, as well as the 1.9's.

From the Dasher Bentley, the available headgaskets for the 1.5 are:

2 notch: 1.3mm thickness
3 notch: 1.4mm thickness
4 notch: 1.5mm thickness
5 notch: 1.6mm thickness

And for the 1.6:

1 notch: 1.4mm thickness
2 notch: 1.5mm thickness
3 notch: 1.6mm thickness

So a three notch 1.6 headgasket is identical to a 1.5 engine's 5-notch.