Sprite Race Motor Rebuild

Discussion in 'Classic Mini' started by Minidave, Mar 1, 2021.

  1. Minidave

    Minidave Well-Known Member
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    Watch this space - it promises to be ugly based on the description!

    No compression on #3, and it was blowing out a whole lot of oil, so my guess is a hole in #3 piston.

    We need a quick turnaround on this one, he has a race in 3 weeks at Hallet and since he didn't finish his weekend at Houston - it ran great for 2 1/2 days! - they won't punch his ticket till he runs one more event.

    His other option is to pull the motor and gearbox out of his Lotus 7, which is the one with the straight cut gears I built a short while ago, but we'd also need to change the cylinder head as it's aluminum and he can't run that.

    We'll see in a couple of days when he hauls it over and I tear it down.....I already made arrangements with the machine shop to slide it in ahead of other work so we can get it right back out again.....but three weeks might be cutting it close, depending on how long it takes to get parts.

    Really miss my local Brit parts supplier, Victoria British!

    Clancy sold his spare race car, so if this engine runs well I may get to build another for him, he already asked me to build him up another straight cut gearbox so I have another set of gears on the way.
     
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  2. MCS02

    MCS02 Moderator
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    Can’t wait!
     
  3. 00Mini

    00Mini Well-Known Member

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    Sounds like it’s going to be a very interesting build given the stated parameters.
     
  4. Crashton

    Crashton Club Coordinator

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    Hey Dave, I knew the owner of Victoria Secret went to the big parts room in the sky. When did the shop close? Did Moose Motors buy them out?
     
  5. Minidave

    Minidave Well-Known Member
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    #5 Minidave, Mar 2, 2021
    Last edited: Mar 2, 2021
    Yep, Moss bought them and promptly shut down the local warehouse sometime in late Dec.

    He's bringing it over tomorrow morning, I'll pop the head off and see what I can learn.....
     
  6. Minidave

    Minidave Well-Known Member
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    Well, this engine turned out not to be so dire after all - it still will need major surgery but once I got the head off I expected to see a hole in the piston or the side melted off - none of that happened!

    The engine is a bit of a mystery in that the parts list of race parts dates from 2009, and I'm not sure all those parts are still in it. It does still have the $600 flywheel and clutch tho!

    IMG_20210303_105942R.jpg

    For example, 2 of the pistons had pretty good marks on them where a valve has hit, one of the intake valves is different than the others, although it's not in either of the cylinders that have the valve marks on them. One of the pushrods is bent, tho none of the valves are stuck, all the guide look good etc. and one of the 8 pushrods is different than the others! The front two pistons have different markings on them than the back two.

    IMG_20210303_110948R.jpg

    Also, stem seals are on the list, but not on the head....

    So, it may have started out pretty racey and has been bodged a time or two over the years.

    We're trying to get a set of +40 pistons, if we can't we'll get some +60 and bore the block. If we can get the +40 then we'll just give it a light hone....as long as the cylinders measure out OK, there is no damage to the cylinder walls at least.

    The cam is supposed to be a "scatter" cam, but I sure can't see any difference in it other than the lobe width - the cam is undamaged, but several of the lifters are showing damage, as do the rear main bearing, the rear cam bearing and the oil pressure relief valve, which was stuck solid and full of metal bits.

    Another interesting tidbit, normally the piston crown comes up to about 5 thou below the deck surface, #1 piston was 3 thou below, all the others were 5 thou over the top of the deck!

    The owner is taking the block, head, pistons and cam up to Kent Prather tonight to have him take a look and make some recommendations, but I think it will be a pretty simple rebuild. The owner has no idea about what his timing, valve clearances or air fuel ratio were......so he has some work to do to learn this motor.

    Now - the damage. #3 piston - which had the lowest compression - has no tension on the top ring, it has a slight amount of burning damage on the side above the top ring, but nothing else and the top ring was not stuck. #4 piston had a broken top ring, but no other damage, the other two were also fine. Not so bad, huh? However if this engine is running 13-1 compression like he thinks, that will pressurize the crankcase pretty quickly at 7500 rpm!

    The engine does have some pretty racy bits on it, like a 4 bolt center main cap, all ARP studs and nuts on the rods, mains and head, and an 11 bolt head.

    IMG_20210304_105926R.jpg
    IMG_20210304_110617R.jpg
    IMG_20210304_110627R.jpg

    Should be a fairly easy rebuild, given that I've enlisted the owner to clean all the bits before we put it back together....especially all the overuse of RTV sealer! god I hate that stuff!
     
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  7. Crashton

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    #7 Crashton, Mar 4, 2021
    Last edited: Mar 4, 2021
    That's a real shame. I wonder how many people lost their jobs.

    Looking forward to the Sprite engine build. :Stig:

    Ha! love that RTV goop, not. An acquaintance of mine many years ago built a MINI race motor using way too much of that. Some managed to somehow block an oil galley. Bang goes the engine. :Dead:
     
  8. Minidave

    Minidave Well-Known Member
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    Yes, I informed the owner that I would NOT be using that carp when I put it together for him.

    How did you like the "crop circle" on top of the piston?

    Found a much lighter one on piston #1 also.
     
  9. 00Mini

    00Mini Well-Known Member

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    That really is allot of RTV sealant. Hard to believe that someone built a racing engine using that much goop.
     
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  10. 00Mini

    00Mini Well-Known Member

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    I didn’t know what the term “scatter cam” meant so I looked it up. Very interesting approach to increase performance and just another reason why I enjoy these rebuilds so much.
     
  11. Crashton

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    Do you figure those crop circles are due to some serious valve float? When my Fire Arrow dropped a valve there was a lot more carnage. Mr. Sprite was lucky.

    When I hear the word scatter I'm thinking of parts trying to escape the engine. Not different cam timing due to siamese ports.

    As for the slathering of RTV goes a lot of people seem to want to glue the shirt out of their engines. When you see what you found it's the mark of a hack with a wrench.
     
  12. Minidave

    Minidave Well-Known Member
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    The owner has decided to see if he can find some 40 over pistons, turns out one of the pistons had a broken ring land under the ring, pretty much like the last Mini engine build I did. If he can't find the 40's Kent Prather at Prather Racing has a set of 60 over he can buy. Still looking for a rimflow intake valve to replace the oddball one.

    He's taking the block back up to Kent's shop on Tuesday to do some of Kent's secret modifications (they're not that secret - I told him about them already :) ) to make it more durable as a race engine. We're really trying to get it ready in time for the race at Hallet on March 19-21, but that's a big ask if we have to wait for parts. We also need to get the block over to the machine shop either to get honed or bored depending on which pistons he goes with.....the machine shop has agreed to slide us in ahead of other work, but it still takes time. so does a proper assembly of the engine, then we have to get it running in the test bed for a bit.

    I really think this engine has been cobbled up some over the years since it was first built so we're going to straighten it all out - the bones are good, we just need to get everything set up correctly.

    I think the valve impression in the one piston is just part of a series of events this motor went thru - it seems to me it was just "put back together" to get it sold, but it has some good race parts in it so I think we can build a good motor out of it once we're done.
     
  13. Minidave

    Minidave Well-Known Member
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    He decided to go with the 60 over pistons Kent has, so we'll get the block over to the machine shop on Wed, if they turn it out quickly enough we'll have it together just in time for a quick run in before he hits the track.
     
  14. Minidave

    Minidave Well-Known Member
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    all righty then, lots done on this race motor, care of Kent Prather (who's also retired but failing at it too :) ) Today they overbored the oil gallery holes, then threaded them for allen grub screws. They found a couple of bad valves so they changed them all and did a light three angle cleanup of the seats.

    He also supplied the owner with new push rods, gasket sets, rod and cam bearings and a few other bits and bobs. main bearings are on the way and will be here Fri I'm told.

    He also decided to go with the 60 over pistons Kent had, so we'll be sending it off to be bored and finish honed tomorrow - I'm hopeful my buddy at the machine shop can slide us in and get it done by Friday afternoon, he said he thought he could but if he's slammed he may not be able to get to it as quickly as he hoped.

    They also balanced the rotating assembly, so once all the stuff arrives it should be an easy assembly process.
     
  15. Minidave

    Minidave Well-Known Member
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    OK, the block and old rods/pistons went to the machine shop today, I'm hopeful he can get it done by Friday, but we won't have rings and rod bearings till Monday, so that will slow things down a bit too.

    Kent apparently found a lot of things wrong in the head, bad valves, one seat that needed to be recut and so on. He also said no two lobes on the cam were the same lift, so a new cam will be in the works for the next time it gets torn down. :(

    This engine definitely shows signs of detonation, and it has been bodged together with an assortment of oddball parts, two pistons that were different from the other two and so on, but if you want to piss with the big dogs you have to lift your leg as they say, so he's buying the good stuff and he'll get more as the season goes along. The pistons he got from Kent were forged and 70 thou oversized custom made pistons - the max you can do without offset boring the block. Kent has used them for years, so they're a known quantity....that's the kind of stuff you need to do if you're going to win races - and Kent's engines win races - and championships.

    I don't know how many races a season he's planning to do (or can afford to do!) but this will get him thru the weekend and get his license punched.

    Funny thing is, he went racing without checking the timing, fuel ratio or pretty much anything before he hit the track! I wonder if he even checked his tire pressures! Oh well, you learn you grow! ;)
     
  16. Minidave

    Minidave Well-Known Member
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    Surprisingly, my guy got the Sprite block bored and finish honed this afternoon, tomorrow he'll hone the wrist pin holes in the pistons and I should be able to pick it all up tomorrow. He did us a real favor getting it pushed in ahead of some other work, but he said he had a opening pop up in his schedule, so he slid us in and got it done.

    I still have lots of things to do to the block before it's ready to assemble, and if the bearings and such come in for the 998 I'll build it up this weekend first. I'm still waiting for the transmission and head to come back for the 998, so all I can do is the block build up on it for now.

    We won't have rings or rod bearings for the Sprite motor till Monday at best, so it will wait till then, but I should have everything ready to go together, so it will be a quick assembly and into the engine stand for a lite break in, retorque and re-adjust of the valves.

    Then he can haul it off and drop it back in the car, but the actual break in will happen when he hits the track. Kent says he can run the first session on the break-in oil, keeping the revs below 6K, then drain and change the oil and go for it in the second session.

    I'll have pics when everything comes back to me.
     
  17. Minidave

    Minidave Well-Known Member
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    The block came back from the machine shop pretty clean, but I still spent a good part of the day using a scotchbrite pad on all the bearing surfaces, running a tap in every hole - some of which were really crudded up - and getting rid of the last tiny bits of red RTV (man I hate that stuff!)

    Once it was all clean and ready I went ahead and installed the new cam bearings - by the way, 998 and 1275 cam bearings are different after all. I never paid a lot of attention to how since they use the same camshafts, but since the block is smaller, the rear cam bearing on 998's is about half as wide as those used in a 1275, and the middle bearing is smaller too. That's the only difference that I can find.....

    IMG_20210312_102649R.jpg

    With the cam bearings in I cleaned out the lifter holes with a rotary wire brush just to make sure they were completely clean and slipped the new lifters in, then installed the cam and oil pump.

    There's not much more I can do in the block till the piston rings and main bearings get here, but I have plenty to do on the cylinder head yet. I'll lightly reface the rocker arms as we're going to reuse these standard arms, then Kent supplied us with a "competition" rocker arm shaft, so I'll install that and get them all set up.

    I've already cleaned all the main parts, but I'll still need to clean up the threads on all the bolts.

    I'm hopeful that the rings and bearings will hit today, but if we don't have them by Monday there's little to no hope of making the race next weekend. If we do get it done I'm thinking of going, it's only a four hour drive and I have a lot of friends going, I could help Clancy with his sales efforts too. He's taking his trailer - he's developed a gig to go to the races and sell parts and such - he's a Griot's dealer, Milwaukee Fuel tools, and lots of specialized Sprite race parts, including the transmissions I build for him. I applaud him for his entrepreneurship!

    A few shots of the cam tool in action - thanks again to my friend WillieB for making the last bushing I needed to complete the set. The paint marks help me align the holes in the bearings to match the oil ports in the block. You also have to watch to make sure the bearing doesn't rotate as it's going in - I've had that happen a couple of times.

    IMG_20210311_132955R.jpg
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    IMG_20210311_133633R.jpg
    IMG_20210311_135203.jpg
    IMG_20210311_135524R.jpg
    IMG_20210311_173506R.jpg
     
  18. Minidave

    Minidave Well-Known Member
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    It's raining all weekend, so I'm down to cleaning and painting things.....ooooooh! Shiny!

    It's just good ol Rusty O'Leum, as this is a race motor and will be apart many times over it's life, in fact I expect to tear it down again after the season is over. At that time we'll probably do a new cam, put in hardened seats and do a full race valve job, plus a few other tricks of the trade.

    IMG_20210312_121234R.jpg
    IMG_20210312_121243R.jpg
    IMG_20210312_121356R.jpg
     
  19. Minidave

    Minidave Well-Known Member
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    Oops, found this today.....

    This goes hand in hand with the bent pushrod and the "crop circle" in the top of the piston. Funny that they ran it like this because, look how far out the adjuster is to compensate for the bent pushrod.

    IMG_20210312_145926R.jpg
     
  20. 00Mini

    00Mini Well-Known Member

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    One tough little motor to withstand all the abuse that had been done to it.
     

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