Piston failures

Discussion in 'Workshop Forum' started by speedy fiat, Dec 29, 2019.

  1. speedy fiat

    speedy fiat Daily Driver

    Location:
    United Kingdom
    I finally braved the damp miserable weather to get into the garage and pull the engine part to investigate the issues of excessive breathing with my Uno Turbo engined X1/9 . Although the engine was completely rebuilt less than a couple of thousand miles ago a strong initial suspect was the inadequate fuel management system fitted when I first installed the engine.
    To help in my diagnosis I found this handy guide to all things related to piston and bore damage.
    https://www.memoparts.com/img/cms/Documents/Piston Failue.pdf
    My initial suspicions have been confirmed as damage as a result of over fueling stripping the piston and bore of lubrication. .
    I've already upgraded the fuel system to something that can actually meet the requirements of a 180-200hp engine. I'll get the crank,etc checked while the engine is apart. The block will need liners installing as it is at maximum oversize. Another set of forged pistons will be required as well.
    My expensive lesson learnt is to keep my ambitions in an achievable balance with my available resources and visa versa. Obviously I'll ignore that maxim at the first opportunity :);)
     
    PaulD, kmead and Dr.Jeff like this.
  2. carl

    carl True Classic

    Location:
    Virginia
    I think a lot of us can get away with errors in tuning in a non turbo motor but strap a turbo on and all bets are off...which is why I'm fine with factory turbo cars as daily drivers but would never even think of adding a turbo like you brave souls.

    Two strokes were the same. Back in the day when I was racing a modified Yamaha RD-250 I was seizing pistons about every other race but back then I really had no clue what I was doing in regards to tuning. My solution was to park the bike and start racing four strokes!
     
  3. lookforjoe

    lookforjoe True Classic

    The ignition system is equally if not more critical. Without very careful monitoring and adjustment you will blow head gaskets and melt pistons in short order. Easy enough to do on a modified NA, add a turbo and it's gonna happen in an instant of lean miss.

    I have plenty of experience with that during years of adding ever larger turbos to Volvo's, whilst tuning myself. All to easy to get carried away when it just feels so good - so why not turn up the wick just a little more ? :D
     
  4. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    That sucks. I'm curious what pistons you were using and what ones you will be getting?
    By chance any pictures of your damage?

    I like that reference you linked.
     
    Last edited: Dec 29, 2019
    Eastep likes this.
  5. speedy fiat

    speedy fiat Daily Driver

    Location:
    United Kingdom
    The attached picture shows the damage to the top piston ring causing the poor compression, all four are similar. The pistons are generally okay apart from a cracked section between the top and second ring on one piston. The bores have been scored, especially at the top. The big and small ends are undamaged. I would agree that the damage is not just fueling but also ignition related, both have been addressed by a decent ecu and some extra sensors. The only choice I seem to have for forged pistons are Wossner, anybody got any comments good or bad about that make?
     

    Attached Files:

  6. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Unfortunately I have the same question. That was why I was wondering what you had (the current ones you pictured), just for reference. Where they forged? They don't look like stock type pistons and I believe you said they are oversized, so I'm assuming they are aftermarket. Wossner or ?? And were they specifically designed as "turbo" pistons?

    I'm trying to learn more about this for my build. I realize there are specific piston designs for boosted engines, however I haven't found any available for the SOHC (1500 bore sizes). I spoke to all of the major aftermarket (and stock) piston makers at the SEMA Show but none of they were able to offer any help for this application. They can all make them custom for a price, but that price is almost more than the total value of my project. So I'm wondering the same question as you.
     
  7. speedy fiat

    speedy fiat Daily Driver

    Location:
    United Kingdom
    The piston in the picture is a Mahle, not forged. That decision was based on price and advice given that they should be able to handle the power outputs I was putting through them, however the (very reputable) company who gave that advice didn't know I had at the time I had a crap engine management system and so I cannot blame them for the end results. I have an increased my knowledge and budget and so will go forged pistons and rods which will be significantly more cost than the none forged, but for my use much cheaper in the long run.They are .6mm oversize, the maximum possible hence the need for a resleeve. Easy enough to get off the shelf over here for the Uno turbo engine. The standard bore and stroke of the 1.4 Uno turbo engine is 80.5mm x 67.5mm and 7.8:1 compression. Unsurprisingly most of the small turbo engine cars (Uno Turbo, Punto Gt, Renault 5 Gt turbo, etc) didn't last long in once they got into the hands of budget strapped amateur tuners.
     
  8. BEEK

    BEEK True Classic

    Location:
    Clermont Fl
    that damage is caused by detonation. need to fix and stop that
     
  9. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Thanks for the added info. In my case piston options for the 1500 will be completely different from you with a UT engine. Initially I will retain the stock pistons with the turbo. However keep in mind my setup is for a max 8psi boost, I'm running a aftermarket ECU and associated engine management, and I will tune it very conservatively. All due to my goals being quite different - I am only looking to wake up a stock engine a bit, not build a track or high performance engine. I have no doubt the stock pistons will not last, but hopefully in the meantime I can learn enough about how to do things better, and find a proper tune, so when new forged pistons go in everything will be ready. Another reason I'm not going directly to custom pistons is my block is still stock bore and in great shape. So I'll wait until it needs to be machined to fit new pistons. If it helps you any, I posted a thread about my experience discussing X1/9 turbo pistons with the manufacturers at SEMA:
    https://xwebforums.com/forum/index.php?threads/stock-piston-specifications.37798/
     
  10. Simon Oaten

    Simon Oaten Daily Driver

    what is the type and material of the mahle ring-set........

    it looks like it has fractured the top ring, and potentially "butted" the oil ring. 2nd ring - if a inlaid type - looks like it has got close to melting the inlay ?

    gaps are basically the "expansion" allowance for a given heat load .......so any abnormal combustion (read higher temp and/or pressure) reduces the end gap - until the ring ends touch ....... this normally leaves vertical lines in the bores. what were the gaps when built ?

    they make 81.5 and 82.0mm slugs in south amrecia for both the 128 1116cc and uno T type engines

    what did the ign map look like ?, comps for IAT / ET / detonation.

    Ignition with every turbo engine is critical to survival
     
  11. speedy fiat

    speedy fiat Daily Driver

    Location:
    United Kingdom
    Sorry I dont have a record of the ring material. The gaps were as per factory setting which is 0.25>0.5mm depending on which if its the first second or oil control rings. The old engine management system was based on the original equipment and so extremely crude to the present system. The speed at which the orginal ecu could process information, the number of information inputs it could cope with and the ability to effectively adjust boost, fueling and ignition to suit were basically not adequate (or there at all!) for what I was asking .
     
  12. Simon Oaten

    Simon Oaten Daily Driver

    no probs !

    to chk - have a close look at the end of each ring - if its "shiny" - its (very) likely they have touched.

    for ring end gap,

    std is in the .004 - .0045 per inch range

    a good starting point (chk with the manufacturer of piston) for moderate boost - .005 - .006 per inch. oil rings will need a bit less

    chk your ignition curve very very very carefully
     
    speedy fiat likes this.
  13. lookforjoe

    lookforjoe True Classic

    Wiseco should be able to make any piston set you desire. The ones I had made a few years ago were for the 1600 were 87mm bore. I don't recall the cost, probably in the $300-$400 range.
     
    PaulD likes this.
  14. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    When I spoke to several companies about it I was hearing much higher numbers for custom pistons, like more than twice that. For me it isn't worth the expense considering what I'm attempting to do, but for others it would be.

    I heard from a guy in Europe that built a turbo engine for his Fiat and he used turbo specific forged pistons from a VW of some type. The bore was correct but the crown height was off a bit for the compression ratio he wanted. He compensated for that another way. He also had to use different small end bearings to make the pins fit the Fiat rods. However I believe there are VW rods that fit the Fiat crank? The point is he got very high quality pistons off the shelf at an extremely low price. He has been running them for a few years with no problems. So there may be more than one way to go about it. But I'm not certain how realistic it might be to find the exact combination that you want for the block size and engine build.
     
  15. Bjorn Nilson

    Bjorn Nilson Daily Driver

    Location:
    Sandared, Sweden
    Scary reading. I am just about to install my UT 1.3l engine. I don't know much about it except it has never been started after overhauling. It has new rings, bearings etc. but stock pistons. I've been told that the engine is bullet proof and good for 250-260hp with stock internals, but a proper ECU is needed. Yesterday I got the MaxxECU Race engine management system and it seems promising so hopefully it will save my engine.
    I had a look at a couple of crazy UT builds in EU. They have 3-400hp and they obviously replaced stock internals (and most everything else). Many of them use pistons from CPS so maybe you should have a look at their offerings.
     
    Dr.Jeff likes this.
  16. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Bjorn, I think it will depend on how far you intend to take your engine. I'm of the impression the stock UT internals will be good as long as you do not try to get to "300-400 hp" with excessive boost levels. By setting a reasonable goal for the boost, and with a good tune in your new ECU, it seems those engines hold up very well. Have you determined any goals for what you want out of it (boost level, HP/torque numbers)?

    For me it might be a little different. I'm using a stock X1/9 1500 engine, not a UT engine. The 1500 was not designed for boost like the UT was. I really don't know how different the UT's internal components are (in terms of their materials and construction) to my 1500's, so I'm going very conservative with the boost and management (around 8 psi, and mild ignition timing). Also managing the heat levels will be important - both the combustion (intake charge, flow restriction) temp and overall engine (oil and coolant) temp. I'm using a large intercooler/pipes/etc, head/exhaust mods, and lots of thermal management. I think the stock UT's intercooler, oil cooler, and other related items could definitely be improved upon and will help keep the stock internals together.

    It seems aftermarket turbo specific pistons are much more available for the UT (like the CPS items) than for the 1500. That was my earlier point about finding pistons from other vehicles (like the VW example I cited). If turbo specific pistons with the right bore, height, pin, etc could be sourced from some other engine to fit my 1500 block, then they will most certainly be more available and affordable than having custom ones made.
     
  17. Bjorn Nilson

    Bjorn Nilson Daily Driver

    Location:
    Sandared, Sweden
    I noticed that CPS have forged race pistons for X1/9 1500 and they can make variants to fit special requirements. Obviously they are doing good stuff but I don't know the cost.
    My build is on a budget and I am trying to use "standard" components as far as possible, so no special pistons if not necessary. I am building my engine with Volvo fuel pump, turbo etc. and whatever is available to keep the cost down. But reading this thread is scarying me and I rather spend some money on pistons NOW, than spending even more money on re-boring cylinders and buying new pistons later. On the other hand I am not in the drag racing business and the car will just occasionally run on track so maybe I should trust the super modern ECU for protecting me from disaster. So maybe no need to worry. In your case I wouldn't worry much as I am sure stock internals will handle the extra load from a light turbo. But I am going for +200 hp just like Speedy Fiat.
    Found CPS worth mentioning from this crazy video:
     
  18. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    From what I've been able to learn, the tune (ignition timing map, AFR map, etc) has much more influence on how well the engine lives than the use of special internal components - within reason. Meaning if someone was building a 400hp drag race engine then the internal components must be capable.

    The two main things I've found about turbo specific pistons are the height of the top ring landing (between the crown and the first groove) and being forged construction. The top landing is the area most prone to damage from detonation (it's a hot spot), and forged offers more overall strength from cracking under high loads. There are other differences, such as compression ratio, but they can be accomodated in other ways or are less vital.

    But as you can see, if you tune the management to prevent detonation, and you don't have excessive pressure levels (high boost), then even those two main features for "turbo" pistons are not as critical. As it was stated to me, it is better to prevent events like detonation from happening in the first place, than to try and accommodate for it after it happens. And most aftermarket ECU's allow you to set protection limits for critical things like temps, detonation, boost level, etc.
     
  19. speedy fiat

    speedy fiat Daily Driver

    Location:
    United Kingdom
    As Dr Jeff says if you can avoid detonation at all costs. Keeping the fuelling under control and the boost down also helps greatly, but this is only possible with decent components such as the inter/charge cooler and the specification of the turbo, ecu, etc. Turbo charged systems do allow seemingly easy and massive gains, but the more standard the components the shorter lived the engine in close correlation to the power increase.
     
    Dr.Jeff likes this.
  20. Dr.Jeff

    Dr.Jeff True Classic

    Location:
    Sin City
    Well stated. That was my point, it depends on the goals and intended level of power increase (i.e. boost). If your goal is a street car (vs race/track only) and therefore you are realistic about the boost levels, then you won't necessarily need to swap everything to race level components. Some items may be more prone to damage/failure than others (likely the pistons and exhaust valves first), so if your goal is to push the boost up then you might want to start with improving those items. The rods can be an issue on some engines, but bottom ends on these engines seem to be rather robust, so I don't think they will be an issue until you go really high boost. In my opinion it really depends on how far you intend to take the performance level.
     

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