Most liked posts in thread: Sprite Race Motor Rebuild

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.

 

The owner knew that his engine was running pig rich, but when he tried to adjust the mixture (done by raising or lowering the jet on a SU carb) the jet wouldn't stay up. On looking at it I could see that the choke linkage was holding the jet down and that it was bent in all sorts of weird ways - that's how the choke works - it drops the jet down to richen the mixture and the return spring in the linkage draws the jet back up and holds it against the adjuster. So I took the link off and reconfigured it and viola! now it works!

I had to straighten the bend on the end where it attaches to the jet, square the first bend coming off the linkage as it was only about 60*, then re-bend the jet end in a different place to shorten it. It was actually a little tough to do as this metal is pretty stiff, I couldn't bend it with pliers, I had to use a hammer and the vise. Which tells me someone bent it that way to begin with, and/or these carbs have been messed with like everything else on this engine so far.





One more thing off the list.

Still waiting for main bearings and rings so I can build the block. The head is done, I rebuilt the rocker arm assembly with a new shaft and refaced the surface of the rocker that hits the valve, so the head is ready to go on when the block is done. This rocker assy is a short term solution, when we re-do with the head later in the year or post season with new hardened seats and new valves we'll put some new roller tip rockers on it.

 

Today I did a "dry build", where you put the pistons in without rings so you can measure a bunch of things like rod bearing clearance and how far the pistons are above or below the deck surface. When I tore this engine down one piston was 3 thou below and the others were about 5 thou over the top of the deck.



Today they are all uniformly 25 thou below the deck, which will make all my other calculations much easier - I don't have to worry about the pistons hitting the head or the valves hitting the pistons.



With that done I installed the rings onto the pistons and put the pistons into the block, then bolted up the caps and torqued them down. Everything still turns nice and smoothly so I put the oil pump pickup tube in and installed the oil pan. Next I flipped the motor over so I could set up the dial indicator and set TDC, then set up for checking the cam timing.





I really need to cc this head, as the calculations I'm coming up with indicate a pretty high compression ratio.....

 

This one is more of a beginner's motor than an all out race motor, tho last time on the dyno it made 108 at the wheels. All out race motors are making more like 145 - 150 at the wheels. The black one I built has not been dyno'd but based on his race pace I'll bet he's close to 140 at the wheels.

Kent Prather at Prather Racing is using E-85 ethanol in his racecar now, it required a lot of changes in fueling and spark, but he gained another 12 hp on his MGA motor - thats a significant number just for changing fuel. He's going to run it this weekend at Elkhart Lake (Road America) if anyone is in the area, it's a fantastic track to watch, lots of shade and great spots to see so much of the track. This weekend is a huge vintage sports car race....over 500 cars entered.

 

Well, DHL was as good as their word and delivered late this afternoon - BUT - unfortunately either I ordered the wrong rings or they sent the wrong rings. Either way, they don't fit. So, I've called an outfit in Ca to see if they have them (APT Racing) if they don't then I'll go to plans B, C and D.....7, Mania and Moss, not necessarily in that order.

I also got in a Moss order today of gearbox parts, so I can build two of the three gearboxes I have waiting. I didn't order parts for the third one because I haven't torn it down yet to see if it's rebuildable and if so what I'll need.

If it is and I can't get them from APT I may go ahead and order gearbox parts along with the rings.

I spent the afternoon figuring out how to mount the engine in my stand, then cleaning the bores and rest of the bits to get ready for assembly. I also ran a tap thru all the holes in the block, and chamfered them too.





I installed the lifters and cam, then laid in the crank and checked the end float. There are probably a few more things I can build at this point but not being able to put the pistons in is definitely going to hold me up.

 

Inside of the block looks like new, doesn't it?

 

Working on getting the rings installed this morning.....I thought I had these pistons all clean and ready but I noticed a LOT of very hard carbon in the top ring groove - but only about half way around each piston, so I'm having to clean them up again.

First scrape all the carbon out, then use a feeler gauge to check and make sure there isn't excessive clearance in the ring groove, the wash them down again with solvent and blow everything dry.

Once they're all clean again I'll put the bearing shells in then install the pistons in the block. Then I'll be ready to drop the head on and and it won't be long till it makes some noise.

Clancy needs to being me a few parts first - distributor, starter and some oil. I have Penn Grade in stock but he uses VR1.

 

Got a little more bark with the straight pipe!

 

I think he said he didn't quite have it all the way into gear when he was pouring the coal to it and when it popped out it was done for. I haven't seen it yet to do a post mortem, but I finished his other box with the straight cut gears so I'm sure he'll bring it by.

 

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!

 

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.

 

They really are.....

Kent Prather is a real guru on these little Sprite motors, his latest version is making 165 hp at the flywheel on the dyno......

Of course, that's a $15K motor too.....or more!

 

Well, as often happens when you want to get things done quickly....parts orders get screwed up and sent to the wrong address and so on ....bottom line rings and bearing won't be here till Thursday at the soonest, so there's no way we can make the race at Hallett this weekend. Too bad, since it's close enough I might have been able to go....still might but it's unlikely at this point.
The next race is at Gingerman, in Michigan, towards the end of April, so that gives us more time for break in and tuning. I won't be going to that one, it's more like a 10-12 hour drive and I doubt I'm up for that - but you never know.

 

Well.....another delay on this build, they sent the wrong rings. So, another call and another set on the way, we'll be lucky if we get them by next weekend!

 

I'm sure he can run a Weber, but he's just getting started so he's going to run this while he builds up his experience and capabilities.

Found the problem with the carbs, and it's embarrassing to say the least. The carbs had some AN3 fittings on the float chambers, and a hose with a hose barb on them too, connecting the two carbs. I hooked my fuel pump right onto that hose barb - not paying any attention to the fact that the AN fittings were the infeed, and the hose was the overflow. So, we pumped fuel in thru the overflow instead of thru the needle and seat - of course it overfueled!

So, tomorrow I'll re-torque the head and reset the valve lash, then fire it up again and run it up to temp. After that I'll pull my carb off and put his back on, but I won't be able to run it with them cause I still don't have any AN3 fittings or hoses....that will be up to him to sort out.

 

2nd test run today, after I retorqued the head and reset the valves....

VID 20210725 1544211 - YouTube