sprint eng rebuild

[DF]

I would Get the Block shotpeened around the crank journals,

[trackerjack]

Yep need good bolts as I once read that a standard 2 litre car engine running at 5000 rpm the piston weighs 2 tons to stop it and throw it back up the bore!

Shot peening the rods would have an advantage Darren but I believe the block is as strong as the weakest link ie the bore has a sharp edge as it meets the main journals, frankly I believe the design and manufacture when compared to modern engines is appalling and not much can be done as their are weak bits all over, ho hum I aint stopping though

Will be making the ladder brace this weekend and will need longer main bolts (100 mm).

Yes Newguy I will piccy it as we go.

[newguy]

Yep need good bolts as I once read that a standard 2 litre car engine running at 5000 rpm the piston weighs 2 tons to stop it and throw it back up the bore!

Shot peening the rods would have an advantage Darren but I believe the block is as strong as the weakest link ie the bore has a sharp edge as it meets the main journals, frankly I believe the design and manufacture when compared to modern engines is appalling and not much can be done as their are weak bits all over, ho hum I aint stopping though

Will be making the ladder brace this weekend and will need longer main bolts (100 mm).

Yes Newguy I will piccy it as we go.

Mean Best news i have Had today Jon

[Dolly racer 33]

Before you get carried away wasting your time making a girdle that does not work, you need to do it correctly or you are wasting your time. Firstly fitting a girdle with spacers across the block with longer bolts is virtually a non starter. Due to production tolerances with blocks you will find a huge variance in the depth the crank is fitted within the block, also you will find the crank is not straight in all blocks, it may be deeper into the block at one end or the other, so manufacturing a plate to fit a variety of blocks with spacers is a non starter. It must also pick up around the outer edge of the block to give any support at all. I have done this for 20 years & I beleive I developed it originally. BL did not use this as it was not homologated for use in racing.

I use 13mm steel plate laser cut & then surface ground down to 12 mm. I also use a stud & nut system to set the plate up on the block, I have these studs made from EN24T. I also use studs around the outside of the block to replace the sump bolts.

As I have said, I have done this for 20 years & regularly rev to 8,500 rev/min occasionally I go to 9,000 inadvertantly but I have still cracked blocks on the mains, If I keep to 8,250revs/min They do not break.

The factory engines revved to 7,200 revs/min with the standard front pulley before the blocks cracked, they then had the Freudenberg damper made which allowed an increase of revs to 7,600revs/min but no more. They never used 8,300revs/min.

I normally sell the girdle kit for £300. If enough people would like me to do a production run I could probably do these for £250 each, plus VAT of course.

Please let me know if you are interested.

Regards.

[SPRINTPARTS]

Ken,

I agree with your ideas, your design sounds very similar to ours, using studs and nuts for the mains and stud/dowels around the outer edge. We broke many blocks before going to girdle plates, even when only running to around 7500rpm. Many years ago we decided to use girdle plates which reduced the number of block failures, but we have recently broken another block even with the girdle plate and 7500 rpm llimit. Unfortunately this motor had also suffered a clutch failure, requiring a clutch change during the race weekend. The clutch had been a balanced unit but we now consider was this the straw that broke the block.

Mark

[Dolly racer 33]

The first block I saw broken was after a clutch failure. One of the securing straps that locate the centre plate on the clutch cover broke so the clutch went off centre, failed. I had a second car do this also. This was when I was using 'full size' organic clutches. I subsequently went to a 'full size paddle' clutch & then on to a 7-25" twin plate paddle. I came to the conclusion that the 'full size' clutch could not cope with the revs I was using.

[DF]

I meant

I would Get the Block shotpeened around the block crank journals,

[trackerjack]

Thanks Ken your input is invaluable as it would seem that whichever way you go there is a weakness to overcome. As far as fitting a girdle for me would be a doddle due to the fact that I am a toolmaker of over 40 years experience, however I do not know why high tensile bolts should be inferior to a stud and nut. It would seem that unless a huge amount of money is spent on all the detail bits the only course is to keep revs to 6500 max.

Cheers DF I am not sure that shot peening cast iron that has been machined is an advantage over just removing sharp edges with a suitable file. I am not being cocky here, I am merely wanting to learn.

[Dolly racer 33]

An Ht bolt is not inferior it is just that to make the girdle a universal fit so it can fit any Dolly block, it needs to be adjustable. I tried the spacer & long bolt route 20 years ago & found that due to the crank being at an angle in the block compared to the sump faces, the spacers had to be at an angle & an individual fit. It is also important as to which way they fit between the girdle & the block, top/bottom, front/rear. So I binned that idea before I started & used studs & have used the same system ever since on all the race Dolly engines I have built.

[Neil907]

What am I missing, how does using a stud over a bolt remove the need for the spacer?

[DF]

Cheers DF I am not sure that shot peening cast iron that has been machined is an advantage over just removing sharp edges with a suitable file. I am not being cocky here, I am merely wanting to learn.

You shotpeen the cast iron girdles, Behind ,the machined surfaces .

The studs are used so you dont have to use machined spacers
Torque the caps down
Install the plate over the studs
measure the distance from the nut heads to the plate
remove plate
install suitable washers and another nut to take this distance up or what gap you require to flex the plate
Put the plate on and another set of nuts to torque the plate down

[Dolly racer 33]

Something like that.

[DF]

Something like that.

I have sort of remembered Ken

[Neil907]

Will that work as well well as properly machined spacers? Do the studs not flex?

[DF]

Will that work as well well as properly machined spacers? Do the studs not flex?

How can they when the plate is pinned to the sump rails