sprint eng rebuild

[trackerjack]

Well folks as a total minimum our sprint has done 2500 miles of track work at or near the red line
In that distance it has had two head gaskets, one due to a heater hose fracture and the other to a cam change.
When the piston ring broke I decided to rebuild it as I had built it in the first instance, the lone damaged piston was replaced by one that Carl on here had sat in his garage
I was amazed to find that the crank journals were all standard and unworn

I was just about to buy all the bits to rebuild when I was dismayed to find that mains 2,3,&4 had a fracture running through the bolt holes had I not spotted it the engine would have broken the crank most likely.

I have three blocks in the garage to choose from but will have to get it bored to suit my + 020" Mahle pistons.

[newguy]

Well folks as a total minimum our sprint has done 2500 miles of track work at or near the red line
In that distance it has had two head gaskets, one due to a heater hose fracture and the other to a cam change.
When the piston ring broke I decided to rebuild it as I had built it in the first instance, the lone damaged piston was replaced by one that Carl on here had sat in his garage
I was amazed to find that the crank journals were all standard and unworn

I was just about to buy all the bits to rebuild when I was dismayed to find that mains 2,3,&4 had a fracture running through the bolt holes had I not spotted it the engine would have broken the crank most likely.

I have three blocks in the garage to choose from but will have to get it bored to suit my + 020" Mahle pistons.

Sounds Good mate.
What Carbs are on that motor?
Actually what are the specs of most of the engine components? The ones you can tell us.
The bottom ends of these motors are fairly strong yeh?

[trackerjack]

Hi Newguy It has and will have Piper 270 fast road cam (this time dialled in using a DTI).
45 Dellorto's
Lightened flywheel
oil cooler (reliability)

Now the stuff thats going to be done.
Dowel the head in place
Gas flow the head and balance the chambers.
Deck the block if possible and make sure pistons are exactly same height.
balance the rods with particular care over the big end.
balance crank together with the flywheel.
A lambda sensor welded into the manifold to check fuel mixture.
check distributer to ensure that it fires 31 btdc on full advance.
I think thats all.
I am looking for 175 bhp.

[SPRINTPARTS]

when I was dismayed to find that mains 2,3,&4 had a fracture running through the bolt holes

Welcome to the world of broken blocks. Unfortunately we have lost count of how many blocks have been detroyed by this method. Usually they break #5, then #4, and if you keep running them then #3. Each broken journal = about 10psi loss in oil pressure.

Mark

[Sprint36]

Hi Newguy It has and will have Piper 270 fast road cam (this time dialled in using a DTI).
45 Dellorto's
Lightened flywheel
oil cooler (reliability)

Now the stuff thats going to be done.
Dowel the head in place
Gas flow the head and balance the chambers.
Deck the block if possible and make sure pistons are exactly same height.
balance the rods with particular care over the big end.
balance crank together with the flywheel.
A lambda sensor welded into the manifold to check fuel mixture.
check distributer to ensure that it fires 31 btdc on full advance.
I think thats all.
I am looking for 175 bhp.

3 angle valve seat cut?
reshape valves?
balance pistons?
manifolds matched to head and dowelled?

David

[newguy]

i was wondering about these 2
balance pistons?
manifolds matched to head and dowelled?

[trackerjack]

The pistons are most likely ok but may need a touch of matching to get them exactly the same weight and height, knowing Triumph I would not be suprised to find that the block face is not true to the line boring.
Oh and yes work on the head would involve progressive valve seat angles plus some smoothing of the ports.
Yes manifold matching plus doweling.
Also going to put two extra tapped holes in on the cam gear wheel.

Tonight I have dug out a near new block that has suffered rust in the std bores and has no cracks on the weak looking journals, I was not impressed with the remains of a cork oil filter that was almost blocking the oil way.
I am thinking of using a company in Cadnam Southampton called Saunders to balance crank etc and bore the block to accept my Mahle +.020" pistons.................has anyone had dealings with them or do you recommend some other place?

When I built my original engine I had it bored an extra .002" to give just a little extra clearance to avoid siezures, any thoughts on this?

[Nick C]

I am thinking of using a company in Cadnam Southampton called Saunders to balance crank etc and bore the block to accept my Mahle +.020" pistons.................has anyone had dealings with them or do you recommend some other place?

I've heard good things about Saunders, though I've not used them personally.

[trackerjack]

when I was dismayed to find that mains 2,3,&4 had a fracture running through the bolt holes

Welcome to the world of broken blocks. Unfortunately we have lost count of how many blocks have been detroyed by this method. Usually they break #5, then #4, and if you keep running them then #3. Each broken journal = about 10psi loss in oil pressure.

Mark

Thinking of bracing the mains with a ladder support made from 2 mm ground stock steel (GFS) what do you guys do cos those main journals look quite weak to me plus the boring runs into them and the machinist has a square edged boring tool rather than a radious.

Thanks Nick

[trackerjack]

Have been checking my "new" block and I am convinced it has not done hardly any miles and is the one that came free with loads of other sprint bits the engine mounts were ripped off so may have come from a crashed car, I have had it for ten years and all the core plugs are shiny so it may be as new. The jackshaft has no discernable wear showing.
I love building engines

[newguy]

We love you building engines to.....

So yea Get us some Pics

[trackerjack]

Took the block, crank, flywheel and conrods to Saunders in Cadnam to have them balanced on Sat.

[SPRINTPARTS]

Thinking of bracing the mains with a ladder support made from 2 mm ground stock steel (GFS) what do you guys do

We use 8mm plate (steel), have also used 10mm aluminium.

regards

Mark

[xvivalve]

2mm doesn't sound much Jon, wouldn't it have a tendancy to tear rather than resist the forces?

I had to supply a new clutch cover for balancing too.

[trackerjack]

Sounds like 8mm GFS then to me thanks lads (I am so used to doing F1 parts that have a short life).