Most liked posts in thread: Sprite Race Motor Rebuild

After I cleared out a few other projects and did a bit of cleanup and organizing, today I pulled the Mini engine out of the test stand and installed the brackets for a Sprite motor.



Next up I laid out all the rings so I could custom cut the ring gaps - since this is a race motor Kent (who supplied pistons and rings) said he wanted 15thou endgap rather than the usual 8-12, so each of the top and second rings had to be filed slightly and re-measured several times till just right, and any burrs carefully cleaned off of the edges.



With that done, next up I cleaned up the crank journals and put in the new main bearings, then laid the crankshaft in. Next I installed the thrust washers, then the studs for the mains, then the center main cap got torqued down. The crank turned smoothly so I did the same with the other two mains one at a time, to make sure if there was any binding I knew where it was. The crank rolls smoothly, so all good there.



The next job was to mount up my dial indicator and check the end play - it should be around 3-5 thou and it was spot on at 3 thou.

The next job will be to install the pistons without the rings and then check all measurements, plastigauge the clearances and check the piston to deck height. When I tore it down 3 of the 4 pistons were proud of the deck by a few thousandths, given how the rods can stretch under high RPM use, you don't want them hitting the head or creating any more "crop circles". If we have that situation I may need to send the pistons off to machine shop to have a little taken off the tops. To that end, I have the old head gasket and I will put some clay on top of the pistons, install and torque the head down and roll it over a few times, then remove the head and see how much room there is - the owner found a deal on some 1.5 roller rockers that he wants to use so I need to make sure the valves and pistons won't meet up!

I also have to CC the heads and then try and compute the compression ratio, he thinks it's about 13:1, and we sure don't want it any higher!

So, still lots to do before it will make noise....his next run is the weekend after our Texas trip so I still have a lot to do.

 

Today I had PT and as usual I was pretty whipped when I got home, but I did get a little work done on the engine. Last night I mocked up a few things to make sure they would work in the engine stand. For example since the oil cooler and assorted hoses stayed with the car I had to rig up a standard spin on oil filter setup so I can run it in the test stand. I wasn't sure the oil filter was going to clear the extra oil pan square.....which it does.




I also put the the head on, and found that the extra two studs must have been drilled by hand, they are a long way from square to the block surface! They will work, but I have to put the head on, then insert the studs.....

Then I moved around the the clutch end and found the pilot bearing was worn badly. The trick to getting one of these out is to fill it with grease, then inset the input shaft just started into the bushing and give it a good smack with a dead blow hammer - the hydraulic effect will force the bushing out of the hole. However, this one was so worn out that the grease would have just squirted out around the shaft sooo......I found a piece of allthread that was a little bigger, and carefully ground it down till it just fit the bushing. Then I did the grease trick and it came out - in three pieces. i think the hydraulic force broke it up.



Anyway, the new one went in without any drama, so I installed and torqued up the flywheel, then installed the clutch assembly, using an old input shaft as an alignment too.





I also called the company in California that supplied this cam and got the scoop on where to set the cam timing - where I might usually set one up at 106* ATDC, they recommended 103 for this scatter cam - glad I called.

More as it happens.....

 

Since I completed this one he's run well at two different race weekends with no issues. Since I finished this one and the car seems to be running very fast, I now have a second race engine in the shop and a third on the way!




Just waiting on a few parts to build this one, they should be here in a day or two.

Everything is cleaned and ready to build

 

When we went to work on Don's Honda motor for his Pup last year we discovered there was no way to use the hoist to put the engine in my engine stand, the legs wouldn't clear.

So when I wanted to use it to rebuild this Sprite motor I had the same issue - the only way I could use it was to take the wheels off the stand, lift the motor with the hoist, set the engine stand on the legs of the hoist then work the end of the attachment into the hole in the stand - it was a right PITA since now the hoist was always in the way.



Today I decided to do something about that, I did some careful measuring and went to the metal supply store yesterday and bought some 1/8" plate, which they sheared into the exact right sizes for me. I also had them cut off some short lengths of 2" square tubing.

Today I drilled a million holes in the plates (well 32 to be exact) and welded the tubes to the plates, then bolted the legs on. Perfect! Now the hoist legs will roll right under the engine stand and I can easily slide the tube into the holder.



Small side benefit, the stand is now about 7" taller and easier to work with.

One interesting note - I don't know how old this made in USA Blackhawk stand is - I've had it for more than 30 years - but the casters were bolted into the stand with metric bolts!

 

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.

 

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.

 

Forgot to post a pic of these custom made 70 thou over forged race pistons....the black on the skirt
is a specialized teflon coating

 

OK, so this is a new one on me - probably because when I was building Sprite racing engines (Team name - Impecunious Racing) in the late 60's they had no such things!

Anyway, the top ring is a standard looking ring, but the second one.....there is a fairly normal looking ring, but on closer inspection the is a dado in the inner part of it, and in the package - a second ring that goes inside the first, and fits in the dado! It should be interesting trying to fit them as the gaps are supposed to go opposite each other. So I guess fit the inner ring on the piston, then the outer - rotate them and hope that when I use the ring compressor they stay together the way they're supposed to!

I've looked them over a bit, and I don't really see how they go together.....but I'll study them some more.....

 

BTW, that's a vernier adjustable timing gear.....

 

Yes, 20-21cc approx. My equipment is not very sophisticated.....need to see if I can find a 100cc graduated beaker. Right now I use a big syringe....

Progress. Cam timing checked. Front end all buttoned up....even made a little pointer to set the timing. Head is on and torqued down, valves are set. Dizzy is in and approximately set. Starter and alternator on, just about ready to set it into the engine stand.....a lot more to do before I can crank up oil pressure, then see if it will make some (hopefully good) noise....

 

Got the engine loaded into the stand this afternoon - today was PT day so that's about all I could do - but I got it mostly wired and plumbed. Filled it with oil, I'm letting it run down for a bit now to see how much it will hold with the added capacity. I already filled up the oil filter. Right now it has 4.5 qts in it, looks like 5 is about all it will take.






I'm using the old header as I sent the new one off to be ceramic coated.

Clancy came up with an old transmission case that I can cut the bellhousing off of and make a cover for the clutch and flywheel, but it will have to be for the next one I build. Too many projects to finish first and this one will be long gone in a couple days or less.

Should be making smoke and noise tomorrow morning sometime.

 

It was 37* at 8 this morning and 61* at noon, so I waited till noon to finish this job....

I re-torqued the head, reset the valve lash, then I fired it up again, which it did easily and ran sweet - made lots of really good noises too!

so it's ready to go home and get dropped into the car again. That will give him time to get all the little niggling bits sorted, plus he bought a Morroso Accusump and he can get that plumbed in too.

Next race is at Eagles Canyon just north of Dallas at the end of April.

 

Made a lot of progress on this motor today, I got the rings on the pistons and the pistons in the bores, rods bolted up and torqued. These ARP bolts require that you use their lubricant (which looks for all the world just like moly lube) in order to torque - most bolts they want clean and dry to torque. I have some of their special lube in stock and use it religiously so no one can come back on me about it if something breaks.



After I got the pistons in I used the dial indicator to find an accurate TDC and set the pointer on the scale so we can set the timing in the future - these engines have the factory timing scale on the bottom of the timing chain cover, so to time one of them you have to lay on the floor and shoot the light upward, while someone else revs it up - to heck with that noise!



With that done I put the head studs in and dropped the gasket on, then the head and put the pushrods in, installed the 1.5 roller rocker set, put all the nuts and washers on and torqued the head down. I adjusted all the valve clearance - I'm going to start this one out at 17 thou to make sure we don't get any coil binding on the springs. It doesn't look like they will but I want to be sure - normal clearance with these is 15 but some engine builders say they get more power with them set a little bit looser.



With all that done I installed the distributor and plug leads - the one that Clancy brought me was a rusted mess. Then I pulled it out of the engine build stand - I'm pleased to say that my engine stand new legs worked exactly as planned, so I could easily pull the engine off the stand and put it up on the bench so I could install the rear plate, flywheel and clutch assemblies.

Clancy also brought me oil but forgot the starter. I'm not sure I can use this fancy schmancy adjustable oil pressure relief valve with a Sprite starter - it looks to me like it won't clear the top bolt and flange. I have a standard relief valve setup if that's the case that I can use while I run it in the engine stand, just as I have to use the Mini oil filter and housing since I don't have the oil cooler that he'll be running.

 

I drained out the extra quart of oil and ran the engine today for the owner and it didn't leak a drop! He was pleased, paid me and hauled it off.

Another successful engine build project comes to an end. Next up, I need to build three straight cut gear Sprite transmissions, hopefully in time for the race at Grattan in 2 1/2 weeks.

 

Today at Grattan he blew third gear in the transmission! The good news is I dropped off Clancy's straight cut gear rebuilt transmission just before they left, so it went in today and he'll be able to run tomorrow.

 

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!



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.



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.





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!

 

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.

 

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.

 

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.

 

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.....



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.