7 replies to this topic

[danie garry]

Good morning All, 

 

the recent adventures of the 998(1977) go a bit like this:

rather disappointing 10.8hp on the rolling road,

a leak down test showing cylinders 2 and 3 loosing its seal just a degree or 2 before tdc(definitely not a timing or valve issue)

remove head on the dyno and hope it's the head gasket and I can fix it there and still get the tune sorted...there was nothing wrong with the gasket(I think I've worked out why the seal dropped, the top 3 or 4 threads for the stud at the front between cylinder 2 and 3 are stripped, either I overlooked it when putting the head on or was just hoping the bottom threads would hold, I will helicoil it)

 

 

so I've stripped the engine for a hone or possibly a re-bore, the bores are a bit scored up but nothing terrible so I'll see if the engine shop thinks its necessary, or if it's worth it while its all apart?

crank seems ok, a 3x6mm oval of surface corrosion on the flywheel end but fine other than that, cam shaft looks fine too but I have no issues with upgrading if it helps? pistons don't look great in my opinion, looks like a lot of rubbing on the skirt(read into that what you will!) 

apart from the obvious(rings, big end bearings, main bearings, seals etc.) what would you guys advise to do, bore to +0.020? new pistons? upgrade the cam? cam bearings? anything in the gearbox? as much fun as it is, I don't fancy taking it all apart in a few months again for something I could do now! minispares order going in soon!

i understand that getting the most out of a re-bore with need some head work, carbs work etc too

 

any help very much appreciated!

 

 

 

 

[sonscar]

Judging by the oil rings it looks to have been neglected and or fairly worn.I would head towards rebore and I am exceptionally mean(and no mechanic either)Steve..

[danie garry]

Judging by the oil rings it looks to have been neglected and or fairly worn.I would head towards rebore and I am exceptionally mean(and no mechanic either)Steve..

The 50,000km on the engine must have been on the same can of oil! I'll be at the car tomorrow so I can give all the parts a good look over, between the bores and the pistons I think it's time for new pistons and a hone so why not go +020

[Cooperman]

It looks as though that is a linered block. In which case a hone might be OK when new pistons are fitted. In fact, it might be possible to just fit new rings. The best thing to do is to take it to a machine shiop for inspection & measurement.

In addition to all new main, big end and thrust bearings, it would be wise to fit nre cam followers, new oil pump, new water pump, timing chain and valve guides.

Then get the valve seats re-cut and thoroughly inspect the valves, especially the exhausts.

It is worth doing some gas-flowing to the head and having it skimmed to increase the compression ratio a bit.

[danie garry]

It looks as though that is a linered block. In which case a hone might be OK when new pistons are fitted. In fact, it might be possible to just fit new rings. The best thing to do is to take it to a machine shiop for inspection & measurement.

In addition to all new main, big end and thrust bearings, it would be wise to fit nre cam followers, new oil pump, new water pump, timing chain and valve guides.

Then get the valve seats re-cut and thoroughly inspect the valves, especially the exhausts.

It is worth doing some gas-flowing to the head and having it skimmed to increase the compression ratio a bit.

 

i didn't notice what looks like liners until i looked at the pics(didn't notice on the deck face anyway), I'll have proper look at it all tomorrow. with the cost of new standard pistons it doesn't feel like much more to go up as size and play around a little. the head is already a recon unit from jonspeed so valves, seats & guides are brand new and the head has been lightly skimmed so the c/r is somewhat unknown but i assume higher than the original

dropped over to the machine shop today but they had closed and wont open until Monday....gotta love public holidays mid week!

any jobs to do in the gearbox?

cheers for the replies!

[timmy850]

On the gearbox it’s always best to strip it down and give a really good clean out.

Check the end float on the lay gear, idler gear etc. Check the clearance on the synchro rings and the general condition of the teeth.

Check the diff pin is still good and the spider gears and washers are still OK

[danie garry]

On the gearbox it’s always best to strip it down and give a really good clean out.

Check the end float on the lay gear, idler gear etc. Check the clearance on the synchro rings and the general condition of the teeth.

Check the diff pin is still good and the spider gears and washers are still OK

I'm thinking by the time I'm that far I'll do a good refresh with the rebuild kit minispares has, judging by the state of the piston rings and cam bearings it looks like oil changes haven't been priority number one!

[danie garry]

a few pics....

cam bearings are only fit for the bin, the cam lobes were a little wiped on one edge

 

weird bit of corrosion on the crank....

 

crank seems ok, will get the engine shop to have a look and see if they think it needs a regrind

Edited by danie garry, 14 May 2021 - 06:49 AM.