pork
Posted a lot
Posts: 1,666
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Had a quick go before work.
All cylinders went to 7bar
Put a smidge of oil down there, and went right up
Cylinder 1- 10bar
2-3-4 - 12bar
What does this mean then?
Cylinder 1 is trashed.
Or is it because I’ve only done 15miles on this fresh pistons/rings
Sent from my iPhone using Tapatalk
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It may just be the angle of the photos, but it looks like the pistons are offset in the bores with quite a large gap - are the pistons the right size?
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pork
Posted a lot
Posts: 1,666
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It may just be the angle of the photos, but it looks like the pistons are offset in the bores with quite a large gap - are the pistons the right size? These are larger pistons than standard, and have had the bores done to match the mm 👍 |
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It may just be the angle of the photos, but it looks like the pistons are offset in the bores with quite a large gap - are the pistons the right size? These are larger pistons than standard, and have had the bores done to match the mm 👍 Good to cross that at least of your list of potential issues. |
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Darkspeed
Club Retro Rides Member
Posts: 4,872
Club RR Member Number: 39
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I would tend toward reading that as they are all trashed just #1 is worse. What were the ring gaps ? I take it the oil was clean and clear with no metallic sheen.
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My take on this for what it's worth- or some things just to consider.
Are your cams to mild for 12:1 compression? You only need a cr this hi to make up for the drop in dynamic cr due to valve overlap on wilder cams.
Are there any dowels in the block or head mating faces? If so make are they are not bottoming out as you have machined the faces. The head bolts won't clamp the gasket if the dowels are to long.
It's half in bits so take the pistons out and check rings/lands. If pistons are ok and if there is enough meat on the piston CROWN machine them to lower cr and throw the decomp plate.
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pork
Posted a lot
Posts: 1,666
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Well I’ve tried it again.........😂😭
Won’t start, compression gone back to 7ish bar
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That's breathing badly. I think pistons need to come out
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pork
Posted a lot
Posts: 1,666
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Hahaha yeah.
Right, order new head and do away with Decomp plate.
Check pistons.
Done
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How thick is the decomp plate and might be random but do you know roughly what thickness a decomp plate ideally wants to be to sort the ratio on a standard cg head-turbo conversion?
I haven't properly looked into ratio's yet because it's still just a consideration but interested to know if you do.
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pork
Posted a lot
Posts: 1,666
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How thick is the decomp plate and might be random but do you know roughly what thickness a decomp plate ideally wants to be to sort the ratio on a standard cg head-turbo conversion? I haven't properly looked into ratio's yet because it's still just a consideration but interested to know if you do. Most people use standard compression I’ve used 2 head gaskets on my old super/turbo build, held up fine. Once I’ve figured out what’s wrong with mine, this plate will be no use to me👍😉 |
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Yeah I've heard of stock engines holding up fine, just thought it might be a good idea to drop the compression ratio for a bit more boost/long term reliability.
Would be interested, once you've got it sorted let me know mate, depending on how much it will drop the compression by I'll be interested.
Cheers
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That bore scuffing on page 8 happened quickly, can you catch it with a fingernail? Whats your measured piston/bore clearance?
Also, is there some pitting to the pistons? Hard to tell from the pics but it looks like there might be.
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Last Edit: Jun 2, 2018 15:39:26 GMT by baracus
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What PSI are you going to be running your turbo up to? And what compression ratio have you got currently?
11psi will be okay for something like 9:1 with an intercooler - for example.
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1987 Supercharged BMW R1150 Citroen 2cv Hillclimb Monster
1995 Renault Master Mk1 Race Transporter
1994 Mazda MX5 Mk1 / NA Road Going Class Hillclimber
1991 UMM Alter II Crew Cab OM606 SuperTurbo Diesel MegaUMM Overlander
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1979 Lomax 224
2014 VW T5.1 Transporter Kombi Highline
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pork
Posted a lot
Posts: 1,666
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What PSI are you going to be running your turbo up to? And what compression ratio have you got currently? 11psi will be okay for something like 9:1 with an intercooler - for example. Hi This is a high comp n/a build. ......but I messed up my measurements and having to use a Decomp plate on a head I’ve done a lot of work on 😕 Think it’s going to be the rings I’ve broke New plan is replace head wit correct compression ratio , getting that Monday. Take pistons out and check rings. |
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Why would the rings be broken?
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pork
Posted a lot
Posts: 1,666
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Why would the rings be broken? I’m guessing from the massive blow by in the last video I posted. The head and plate have been all torqued and sealed right. Only way for smoke to come out through the breathers is through the rings......right? 🙂 |
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pork
Posted a lot
Posts: 1,666
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Had a spare hour today.
With old stuff I had:
Cylinder 1- 5 bar
Cylinder 2/3/4 - 7 bar
Tried a new head .......
Same results 🤔
Pulled out piston 1.......rings intact, bores look fine, hone marks still there,no signs of damage
Gunna pull engine apart, rebuild, start again
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No they don't, you've got bore scuffing on the pics you posted on the previous page. Post some pics of the piston skirts, tops and undersides before you clean them up. It's probably a clearance and/or heat issue. What exactly did you set the ring gaps at, and what exactly is the piston to bore clearance (measured, not from book and what you asked it to be bored at, we're in the realms of where 0.01mm can be too much) |
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Last Edit: Jun 6, 2018 17:28:56 GMT by baracus
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pork
Posted a lot
Posts: 1,666
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No they don't, you've got bore scuffing on the pics you posted on the previous page. Post some pics of the piston skirts, tops and undersides before you clean them up. It's probably a clearance and/or heat issue. What exactly did you set the ring gaps at, and what exactly is the piston to bore clearance (measured, not from book and what you asked it to be bored at, we're in the realms of where 0.01mm can be too much) Il get on the pics tomorrow 👍 I left that in the hands of the engine recon shop I got to do the boreing What ring gap should I have? Il be able to check once it’s apart. |
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